Papers - NISHIOKA Kensuke
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Future vision of photovoltaics Invited Reviewed
NISHIOKA Kensuke
Oyo Buturi 94 ( 4 ) 193 - 196 2025.4
Authorship：Lead author, Corresponding author Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Applied Physics
Photovoltaic is one of the most promising technologies among renewable energies, and there is a strong desire for the further spread of photovoltaic as a primary source of electricity and the development of new applications. Based on the empirical results, new applications and future vision of photovoltaic will be explained, focusing on solar carport, wall-mounted photovoltaic, and agri-voltaic.
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Public road driving tests of Toyota Prius equipped with high-efficiency III-V triple-junction PV modules Reviewed International journal
Kenji Araki, Yasuyuki Ota, Kensuke Nishioka
EPJ Photovoltaics 16 20 2025.3
Authorship：Last author Language：English Publishing type：Research paper (scientific journal)
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Testing and rating of vehicle-integrated photovoltaics: Scientific background Reviewed International journal
Araki K., Ota Y., Nishioka K.
Solar Energy Materials and Solar Cells 280 2025.1
Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Solar Energy Materials and Solar Cells
We need to rush into the international standardization of the performance of VIPV. IEC TC82 PT600 and WG2 group carry out the standardization discussion. This work covers the scientific aspects behind the standardization. It consists of three layers: (1) Performance testing VIPV or curved PV modules by reproducible measurements; (2) Outdoor performance validation and correction modeling; (3) Energy rating. Unlike other PV installations, the relative position of the sun and its shading objects quickly and frequently moves so that the repeatable evaluation of the performance of VIPV was challenging. As a result of scientists and testing engineers worldwide, (1) we could develop a new testing protocol for the curved PV modules, (2) we observed the different performances in the curved photovoltaic modules and succeeded in reproducing in a simple numerical model, and (3) we developed Excel-level calculation methods for shading and partial-shading impact to irradiation onto photovoltaic modules on vehicles.
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Nagaoka A., Miura S., Nakashima K., Hirai Y., Higashi T., Yoshino K., Nishioka K.
Applied Physics Letters 125 ( 7 ) 2024.8
Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Letters
The lack of attractive n-type thermoelectric materials greatly restricts their applications because most high-performance materials are p-type conductors, such as the kesterite compound Cu2ZnSnS4. This study reports high-quality n-type kesterite (Cu1−xAgx)2ZnSnS4 (CAZTS) single crystals that exhibit a record high dimensionless figure of merit value of 1.1 at approximately 800 K, primarily owing to Ag alloying, cation compositional optimization, and intrinsic low thermal conductivity. An n-type CAZTS-based single-leg device was fabricated using a Mo-barrier layer. The device exhibited a thermoelectric conversion efficiency of 3.4% at a temperature gradient of 473 K. This study provides insights into developing thermoelectric modules using environmentally friendly kesterite materials.
DOI： 10.1063/5.0220909
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Outdoor evaluation of total cross-tied Si module under driving conditions Reviewed International journal
Yasuyuki Ota, Yoshio Ohshita, Keiya Tamada, Kenji Araki, Kyotaro Nakamura, Kensuke Nishioka
Solar Energy Materials and Solar Cells 274 2024.6
Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Solar Energy Materials and Solar Cells
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Vector-Based Advanced Computation for Photovoltaic Devices and Arrays: Numerical Reproduction of Unusual Behaviors of Curved Photovoltaic Devices Reviewed International journal
Araki K., Ota Y., Nishioka K.
Applied Sciences (Switzerland) 14 ( 11 ) 2024.6
Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Sciences (Switzerland)
Featured Application: It is helpful to accurately model any photovoltaic device regardless of whether a single solar cell, module (solar panel), or array of PV modules can be applied if the overall shape (including envelopes) is nonplanar, such as vehicle-integrated photovoltaics (VIPVs), agriphotovoltaics, building-integrated photovoltaics (BIPVs), aircraft PVs, and wavy PV arrays installed on wavy land (mountains, gorges, etc.). Most equations and models for photovoltaics are based on the assumption that photovoltaic (PV) devices are flat. Therefore, the actual performance of nonplanar PV devices should be investigated and developed. In this study, two algorithms were developed and defined using vector computations to describe a curved surface based on differential geometry and the interaction with non-uniform solar irradiance (i.e., non-uniform shading distribution in the sky). To validate the computational model, the power output from a commercial curved solar panel for the Toyota Prius 40 series was monitored at four orientation angles and in various climates. Then, these were compared with the calculation results obtained using the developed algorithm. The conventional calculation used for flat PV devices showed an overestimated performance due to ignorance of inherent errors due to curved surfaces. However, the new algorithms matched the measured trends, particularly on clear-sky days. The validated computation method for curved PV devices is advantageous for vehicle-integrated photovoltaic devices and PVs including building-integrated photovoltaics (BIPVs), drones, and agriphotovoltaics.
DOI： 10.3390/app14114855
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Analysis for Effects of Temperature Rise of PV Modules upon Driving Distance of Vehicle Integrated Photovoltaic Electric Vehicles Reviewed International coauthorship
Masafumi Yamaguchi, Yasuyuki Ota, Taizo Masuda, Christian Thiel, Anastasios Tsakalidis, Arnulf Jaeger-Waldau, Kenji Araki, Kensuke Nishioka, Tatsuya Takamoto, Takashi Nakado, Kazumi Yamada, Tsutomu Tanimoto, Yosuke Tomita, Yusuke Zushi, Kenichi Okumura, Takashi Mabuchi, Akinori Satou, Kyotaro Nakamura, Ryo Ozaki, Nobuaki Kojima, Yoshio Ohshita
Energy and Power Engineering 16 131 - 150 2024.4
Language：English Publishing type：Research paper (scientific journal)
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Design Optimization of Agri-Photovoltaic Systems in Different Climate Regions† Reviewed
Toyoda T., Yajima D., Araki K., Nishioka K.
IEEJ Transactions on Electrical and Electronic Engineering 19 ( 2 ) 208 - 214 2024.2
Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：IEEJ Transactions on Electrical and Electronic Engineering
This paper examines the optimal design for agri-photovoltaic (agri-PV) systems. Agri-PV systems should be evaluated on the total crop yield and power generation, and the balance is essential. Specifically, the amount of solar irradiance reaching the farmland and power generation by PV systems varies by panel separation and tilt angle, affecting crop yield. Quantitative analysis is essential for balancing. This study investigated the balance between the output of Agri-PV installed on farmland and photosynthetic photon flux density (PPFD), a crucial indicator for crop growth, and discussed the optimal solutions for Agri-PV systems installed in various regions. Simulations were conducted for Miyazaki (semi-tropical) and Nagano (inland climate) to understand the changes in different climate regions. Miyazaki has higher PPFD and PV output than Nagano because Miyazaki has more solar irradiance and longer sunshine duration than Nagano. When the normalized panel pitch is small, PPFD changes significantly by the tilt angle. When the normalized panel pitch is large, the profit may be maximized by setting the panel tilt angle to maximize the PV output. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.
DOI： 10.1002/tee.23943
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Shwe Sin P.P., Wai S.H., Ota Y., Nishioka K., Suzuki Y.
International Journal of Hydrogen Energy 53 86 - 92 2024.1
Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：International Journal of Hydrogen Energy
Hydrogen production from renewable electricity offers an eco-friendly alternative to fossil fuels. Proton exchange membrane (PEM) electrolysis is a well-known method for this purpose. Studies have primarily focused on reducing costs of noble catalysts, improving efficiency, managing system degradation, and addressing membrane thinning caused by contaminated cations. However, techniques for PEM recovery post-degradation are still under development. This study investigated the effects of cations on PEM cells using artificial soft water, and analyzed two recovery methods to restore cell performance. Our findings indicate a significant rise in cell operating voltage and a decrease hydrogen production over 8 h of operation with soft water. After introducing both recovery methods, the initial operating value was reinstated in both cases. Only nitric acid treatment, however, achieved hydrogen production levels comparable to those of ultrapure water.
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Analysis of Climate Conditions upon Driving Distance of Vehicle Integrated Photovoltaics-Powered Vehicles Reviewed International coauthorship
Yamaguchi M., Nakamura K., Ozaki R., Kojima N., Ohshita Y., Masuda T., Okumura K., Mabuchi T., Satou A., Tanimoto T., Tomita Y., Zushi Y., Nakado T., Yamada K., Thiel C., Tsakalidis A., Jaeger-Waldau A., Takamoto T., Araki K., Ota Y., Nishioka K.
Energy Technology 12 ( 1 ) 2024.1
Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Energy Technology
The development of the vehicles powered by photovoltaic (PV) is desirable and very important for reducing CO2 emissions from the transport sector to realize a decarbonized society. Although long-distance driving of vehicle-integrated PV (VIPV)-powered vehicles without electricity charging is expected in sunny regions, driving distance of VIPV-powered vehicles is affected by climate conditions such as solar irradiation and outside temperature, and the power consumption of the air conditioners. In this article, analytical results for system efficiency of VIPV-powered vehicles and the effects of usage of air conditioner are presented by using power losses estimated from the electric mileage by using the driving distance data for Toyota Prius and Nissan Van demonstration cars installed with high-efficiency InGaP/GaAs/InGaAs three-junction solar cell modules with a module efficiency of more than 30%. The potential of VIPV-powered vehicles to be deployed in major cities in Japan and the world is also analyzed. Mild weather cities such as Miyazaki in Japan and Sydney in Australia are thought to have longer driving range even under usage of air conditioners. The other power losses for the VIPV such as temperature rise of VIPV modules and partial shading estimate the previous data and some reference as well as effects of usage of air-conditioners are also discussed in this article.
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Thermoelectric material ZnSnAs2 showing high power factor below 200°C Reviewed
Nakashima Koki, Nagaoka Akira, Nagatomo Katsuma, Hirai Yuichi, Nishioka Kensuke
Journal of Ternary and Multinary Compounds 2023 ( 0 ) 47 - 50 2024
Authorship：Last author Language：Japanese Publishing type：Research paper (international conference proceedings) Publisher：The Japan Society of Applied Physics, Professional Group of Multinary Compounds and Solar Cells
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Evaluation of thermoelectric conversion efficiency of multinary thermoelectric material Cu2ZnSnS4 by simulation Reviewed
Nagatomo Katsuma, Nagaoka Akira, Nishioka Kensuke
Journal of Ternary and Multinary Compounds 2023 ( 0 ) 13 - 16 2024
Language：Japanese Publishing type：Research paper (conference, symposium, etc.) Publisher：The Japan Society of Applied Physics, Professional Group of Multinary Compounds and Solar Cells
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P-09 Social and regional contribution initiatives taking advantage of Miyazaki
YOSHINO Kenji, NAGAOKA Akira, OTA Yasuyuki, NISHIOKA Kensuke, SUZUKI Yoshihiro
Proceedings of Annual Conference of Japanese Society for Engineering Education 2024 ( 0 ) 430 - 4321 2024
Language：Japanese Publishing type：Research paper (conference, symposium, etc.) Publisher：Japanese Society for Engineering Education
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Thermoelectric Conversion Efficiency of 4% in Environmental-Friendly Kesterite Single Crystal Reviewed International coauthorship
Akira Nagaoka, Katsuma Nagatomo, Koki Nakashima, Yuichi Hirai, Yasuyuki Ota, Kenji Yoshino and Kensuke Nishioka
Materials Transactions 64 2535 - 2541 2023.9
Authorship：Last author Language：English Publishing type：Research paper (scientific journal)
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Shimizu R., Ota Y., Nagaoka A., Araki K., Nishioka K.
Applied Sciences (Switzerland) 13 ( 18 ) 2023.9
Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Sciences (Switzerland)
Featured Application: Solar panel fire accident diagnosis, analysis, and prediction. Fires in photovoltaic modules are caused by hot spots, which are typically monitored by thermal images. This method helps visualize the hot spot, but it is affected by the environment (solar irradiance, wind, ambient temperature) and is not reproducible. Assessing the heat dissipation of the hot cell can be used for alternative assessment of the fire risk. This method was validated by comparing the value measured by the surface potential meter and the module potential measured directly by adding a bypass measurement circuit. The substantial reverse-bias voltage caused by mismatching or partial shading (depending on the operating conditions) leads to local heat consumption of the partially shaded solar cells and potentially causes fire. The fire risk can be assessed in the worst-case conditions (ex. 1380 W/m2 solar irradiance) by non-contact measurement of the reverse-bias voltage and calculating the heat dissipation and temperature rise. This work suggested that −13 V is the criterion and was close to the known value of reverse voltage for Si cells. The current technology inspects solar cells before assembly to the module, and there is no way of inspecting in the product test or detecting after degradation that can be covered by the proposed method in this work.
DOI： 10.3390/app131810391
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Araki K., Ota Y., Nagaoka A., Nishioka K.
Energies 16 ( 11 ) 2023.6
Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Energies
Building-integrated photovoltaics (BIPVs) and vehicle-integrated photovoltaics (VIPVs) receive solar irradiance through non-uniform shading objects. Standard scalar calculations cannot accurately determine the solar irradiance of BIPV and VIPV systems. This study proposes a matrix model using an aperture matrix to accurately calculate the horizontal and vertical planes affected by non-uniform shading objects. This can be extended to the solar irradiance on a VIPV by applying a local coordinate system. The 3D model is validated by a simultaneous measurement of five orientations (roof and four sides, front, left, tail, and right) of solar irradiance on a car body. An accumulated logistic function can approximate the shading probability. Furthermore, the combined use of the 3D solar irradiance model is effective in assessing the energy performance of solar electric vehicles in various zones, including buildings, residential areas, and open spaces. Unlike standard solar energy systems, the energy yield of a VIPV is affected by the shading environment. This, in turn, is affected mainly by the location of vehicle travel or parking in the city rather than by the climate zones of the city.
DOI： 10.3390/en16114414
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Direct Observation of Group-V Dopant Substitutional Defects in CdTe Single Crystals Reviewed
Nagaoka A., Kimura K., Ang A.K.R., Takabayashi Y., Yoshino K., Sun Q., Dou B., Wei S.H., Hayashi K., Nishioka K.
Journal of the American Chemical Society 145 ( 16 ) 9191 - 9197 2023.4
Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of the American Chemical Society
Point defect chemistry strongly affects the fundamental properties of materials and has a decisive impact on device performance. The Group-V dopant is prominent acceptor species with high hole concentration in CdTe; however, its local atomic structure is still not clear owing to difficulties in definitive measurements and discrepancies between experimental observations and theoretical models. Herein, we report on direct observation of the local structure for the As dopant in CdTe single crystals by the X-ray fluorescence holography (XFH) technique, which is a powerful tool to visualize three-dimensional atomic configurations around a specific element. The XFH result shows the As substituting on both Cd (AsCd) and Te (AsTe) sites. Although AsTe has been well known as a shallow acceptor, AsCd has not attracted much attention and been discussed so far. Our results provide new insights into point defects by expanding the experimental XFH study in combination with theoretical first-principles studies in II-VI semiconductors.
DOI： 10.1021/jacs.3c01248
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Solar Electric Vehicles as Energy Sources in Disaster Zones: Physical and Social Factors Reviewed
Araki K., Ota Y., Maeda A., Kumano M., Nishioka K.
Energies 16 ( 8 ) 2023.4
Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Energies
Electric vehicles (EVs) have the advantage of being resilient to natural disasters. However, users hesitate to donate electricity when they lose the chance to recharge at the utility. Solar electric vehicles (SEVs) save energy through vehicle-integrated photovoltaics (VIPV) and make it possible to voluntarily donate excess energy, thus maintaining facility resilience. Given that the supply of solar energy to VIPV systems is not continuous and is difficult to forecast, the contribution of VIPV to the resilience of the larger energy system has been called into question. This is the first study in which the potential of VIPV to maintain utility resilience is investigated in the context of physical factors, such as irradiance, and social factors. The actual energy yield of a VIPV car was determined using an advanced 3D solar irradiation model under a nonuniform shading distribution, with validation from actual measures of solar irradiance on five orthogonal sides of the car body. The Monte Carlo method was used to model the complex factors in VIPV energy storage and energy donations under different scenarios. Depending on the climate, population density, and shading environment, the voluntary contribution of stored electricity in SEV is sufficient to provide disaster relief support.
DOI： 10.3390/en16083580
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Yajima D., Toyoda T., Kirimura M., Araki K., Ota Y., Nishioka K.
Energies 16 ( 7 ) 2023.4
Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Energies
Climate change and increasing food demand are global issues that require immediate attention. The agrivoltaic system, which involves installing solar panels above farmland, can simultaneously solve climate and food issues. However, current systems tend to reduce agricultural production and delay the harvest period due to shading by the solar panels. A delayed harvest period impacts the income of farmers who wish to sell produce at specific times. Incorporating a model that calculates the amount of electricity generated by solar irradiation, this study establishes a model to estimate the correct start date of cultivation for solar panel covered crops to ensure the correct harvest date and determines the expected income of farmers by calculating agricultural production and power generation. Using taro cultivation in Miyazaki Prefecture as a case study, the model estimated that the start date of cultivation should be brought forward by 23 days to ensure the ideal harvest period and agricultural production. This would prevent an opportunity loss of USD 16,000 per year for a farm area of 10,000 m2. Furthermore, an additional income of USD 142,000 per year can be expected by adjusting shading rates for the cultivation and non-cultivation periods.
DOI： 10.3390/en16073261
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Electrode Shape Dependence of InGaAsP Photovoltaic Characteristics under Laser Irradiation for Optical Wireless and Fiber Power Transmission Reviewed
Masakazu ARAI, Akira KUSHIYAMA, Yuga MOTOMURA, and Kensuke NISHIOKA
The Review of Laser Engineering 51 ( 3 ) 171 - 175 2023.3
Authorship：Last author Language：English Publishing type：Research paper (scientific journal)
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Yamaguchi M., Masuda T., Nakado T., Yamada K., Okumura K., Satou A., Ota Y., Araki K., Nishioka K., Kojima N., Ohshita Y.
IEEE Journal of Photovoltaics 2023.2
Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Journal of Photovoltaics
Development of photovoltaic (PV)-powered vehicles is very important to play a critical role in a future carbon neutrality society because it has been reported that the vehicle integrated PVs (VIPVs) have great ability to reduce CO<sub>2</sub> emission from the transport sector. Usage of high-efficiency solar cell modules is essential due to the limited installable area of PV on vehicle exterior. This article presents test driving data of the Toyota Prius demonstration car installed with high-efficiency III-V compound triple-junction solar cell module with an efficiency of more than 30%. Average daily driving distance (DD) of 17 km/day under usage of air conditioning and 62% CO<sub>2</sub> emission reduction are demonstrated by actual driving in Nagoya, Japan. In addition, analytical results for impact of high-efficiency VIPV modules of more than 35% on increases in DD of more than 30 km/day average and reducing CO<sub>2</sub> emission of PV-powered vehicles of more than 70% reduction are also shown.
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Yajima D., Toyoda T., Kirimura M., Araki K., Ota Y., Nishioka K.
Cleaner Engineering and Technology 12 100594 2023.2
Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Cleaner Engineering and Technology
Climate change and increasing food production due to population growth are global challenges that need immediate attention. The introduction of renewable energy to mitigate climate change and the requirement of adequate land to increase food production are generally mutually exclusive. However, an agrivoltaic system generates renewable electricity and produces agricultural products from a common piece of land, thus increasing the land productivity. In addition, this system contributes to local production, thus reducing the CO2 emissions from logistics. Photovoltaic arrays in previous studies were designed by calculating the irradiance in W/m2, even in recent studies. A careful design of the farmland's illumination must be developed for effective agriculture. The simulations must be scaled based on photosynthetic photon flux density rather than irradiance commonly applied in photovoltaic technology simulations. This study focused on the photosynthetic photon flux density and employed an all-climate solar spectrum model to calculate the photosynthetic photon flux density accurately on farmland partially shaded by solar panels and supporting tubes. This study described an algorithm for estimating the photosynthetic photon flux density values under solar panels. The calculated data were validated using the photosynthetic photon flux density sensors. To calculate the photosynthetic photon flux density under the solar panels, it is essential to weigh the direct and diffused components shaded by the solar panels separately because they have different spectrums. A method to quantify the shading was explored here by solar panels and their supporting tubes for the direct and diffused component as the sun moves. The calculation formula was established by defining the sun's moves and the positions of solar panels and their supporting tubes in terms of elevation and azimuth angles from the observation point. It was found that the waveform based on the calculation formula for the photosynthetic photon flux density under the solar panels reproduced the same tendency as the measured photosynthetic photon flux density. To evaluate this trend numerically, the measured and calculated photosynthetic photon flux densities were compared using the standard residuals. Generally, the similarity of the two values is confirmed by a standard residual value between −3 and 3. The result of this study showed that the standard residual values were negative in more frequencies except for the zero photosynthetic photon flux density at night. This indicates that the calculated photosynthetic photon flux density tends to be higher than the measured photosynthetic photon flux density. The peak frequency of the standard residuals was between −6 and −3. This difference probably occurred because the established calculation formula targets the shading provided by the solar panels and supporting tubes but does not cover the shading provided by the other system structures. The calculation formula enables farmers to evaluate the economic efficiency of the system before introducing it using measured solar irradiation data at the target farmlands by introducing published neighborhood solar irradiation data and considering, in advance, measures to avoid the effects of shading on agricultural production. The next study will be to improve the accuracy of the calculation formula by increasing the number of days and develop a method that leads to the best practices of agricultural production and solar power generation by introducing the system.
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Thermoelectric Conversion Efficiency of 4% in Environmental-Friendly Kesterite Single Crystal
Nagaoka A., Nagatomo K., Nakashima K., Hirai Y., Ota Y., Yoshino K., Nishioka K.
Materials Transactions 64 ( 10 ) 2535 - 2541 2023
Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Materials Transactions
Multinary Cu2ZnSnS4 (CZTS)-based materials have attracted considerable attention for thermoelectric (TE) power generation owing to their cost-effectiveness and abundance. The device structure of the CZTS/Au diffusion barrier layer was effective in impeding chemical diffusion during operation; however, its interfacial contact resistance was relatively higher than that of the Bi2Te3 device. We report the discovery of p-type CZTS single crystals with a record-high dimensionless figure of merit (ZT) of 1.6 at 800 K and TE conversion efficiency of 34% at a temperature difference of 473 K, which is based on the Te-free concept. This study demonstrated the potential of CZTS-based TE materials for environment-friendly TE power generation.
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Controlling the conduction type in a thermoelectric material (Cu1-xAgx)2ZnSnS4 Reviewed
Okamoto K., Nagaoka A., Nagatomo K., Yoshino K., Ota Y., Nishioka K.
Journal of Physics and Chemistry of Solids 171 2022.12
Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Physics and Chemistry of Solids
Quaternary kesterite p-type Cu2ZnSnS4 (CZTS) has the potential to be used as an environmentally friendly thermoelectric (TE) material. Conversion of p-n conduction is required for the realization of a CZTS-based TE device. Herein, we studied the growth of a polycrystalline (Cu1-xAgx)2ZnSnS4 (CAZTS) and its fundamental TE properties. An n-type CAZTS (x = 0.4) with a negative Seebeck coefficient (60–70 μV/K) can be obtained without secondary phases. The electrical conductivity decreased with increasing Ag content owing to defect compensation. The conduction mechanism of the polycrystalline CAZTS can be demonstrated through hopping conduction, thermal activation, and a potential barrier at the grain boundary.
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Wai S.H., Ota Y., Nishioka K.
Journal of Power Sources 546 231991 2022.10
Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Power Sources
The solar-to-gas (StG) conversion system is a potential pathway for accelerating zero-carbon energy sources. In our previous study, outdoor StG conversion was accomplished using triple-junction concentrator photovoltaic (CPV) modules. The system achieved the highest performance with sets of DC/DC converters and electrochemical (EC) cells. Therefore, we aimed to investigate the prospective StG conversion from PV systems if such a system is installed in Japan. A power generation prediction model considering all weather conditions, called the Miyazaki Spectrum to Energy (MS2E), has been developed using the METPV-11 meteorological database at the University of Miyazaki. Accordingly, the amount of energy generated by various PV systems could be forecasted nationwide from the global irradiance data. In this study, we applied the MS2E PV energy prediction method and approached the potential StG conversion efficiency of silicon (Si) PV and inverted metamorphic (IMM) PV systems across Japan. Based on the actual StG measurement data, we approximated the conversion of each subsystem. The simulation results show that IMM modules can provide higher StG conversion than Si modules.
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Analysis for the Potential of High-Efficiency and Low-Cost Vehicle-Integrated Photovoltaics Invited Reviewed
Yamaguchi M., Nakamura K., Ozaki R., Kojima N., Ohshita Y., Masuda T., Okumura K., Satou A., Nakado T., Yamada K., Tanimoto T., Zushi Y., Takamoto T., Araki K., Ota Y., Nishioka K.
Solar RRL 2200556 2022.9
Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Solar RRL
The spread of the photovoltaic-powered electric vehicle (PV-EV) is desirable and is essential for reduction in CO2 emissions, increasing electric range, and creating a new clean energy infrastructure based on PVs. Development of highly efficient PV modules with reasonable cost is necessary to realize a longer PV-driving range of passenger cars. Herein, the potential of various solar cell modules for vehicle-integrated photovoltaic (VIPV) applications is analyzed. This article shows that the use of highly efficient solar cell modules with an efficiency of higher than 35% enables longer than 30 km day−1 PV driving under average irradiance of 4 kWh m−2day−1 without external charging. Cost reduction of VIPV modules is also very important for spreading the PV-powered vehicles. By considering electricity charging cost saving and reduction in CO2 emission of electric vehicles, the cost target of VIPV is discussed. The cost targets of the solar cell modules for the PV-EV by considering only electricity charging cost saving, $2.6/Wp for a module with conversion efficiency of 20% and $3.7/Wp for a module with that of 40%, are estimated in the case of electric mileage of 10 km kWh−1.
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CPV standardization 2021 - Maintenance and stability Reviewed International coauthorship
Araki K., Algora C., Kresse D., Siefer G., Timò G., Antón I., Nishioka K., Leutz R., Carter S., Wang S., Askins S., Iwasaki T., Ji L., Kelly G.
AIP Conference Proceedings 2550 2022.9
Language：English Publishing type：Research paper (scientific journal) Publisher：AIP Conference Proceedings
The rapid and substantial decline of the cell-cost, CPV, relied on cell-saving and became less valuable. Many players and systems got off the stage as a result. Also, less and fewer new proposals in the CPV standardization. We decided to continue the standardization activity but separate the tracker's work by creating a new working group, WG9. The technical discussion on VIPV has also been discussed in WG7, and it is to be transferred to a new project team. Besides the existing standards' maintenance work, new proposals of the new CPV standards were posted and approved recently. One is the fire test of the CPV module, and another is a series of standards of the hybrid CPV/PV.
DOI： 10.1063/5.0099174
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Wai S.H., Swe T.H., Ota Y., Sugiyama M., Nishioka K.
AIP Conference Proceedings 2550 2022.9
Language：English Publishing type：Research paper (scientific journal) Publisher：AIP Conference Proceedings
A sustainable, renewable energy source is highly desirable for a zero-carbon-emission society. A powerful energy supply that can replace the fossil fuel sector is required. Effective energy transformation into synthetic chemical energy has become a promising alternative energy production method that can conveniently store energy produced by renewable sources. Solar-to-gas conversion has caught the attention of researchers to provide green hydrogen for vehicles and synthetic natural methane for the current gas-grid infrastructure. Such systems are run on solar energy converted into storable chemical energy such as hydrogen and methane. In this study, a new method was developed by independently setting the reactor temperatures and evaluating the methane concentration and methanation power consumption. Subsequently, a high methane concentration (97.89%) and lower power consumption of the methanation system (0.148 kW) were observed at low temperatures (180 °C, 260 °C).
DOI： 10.1063/5.0099245
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Effects of Artificial River Water on PEM Water Electrolysis Performance Reviewed
Yoshimura R., Wai S.H., Ota Y., Nishioka K., Suzuki Y.
Catalysts 12 ( 9 ) 934 2022.9
Language：English Publishing type：Research paper (scientific journal) Publisher：Catalysts
Hydrogen, a clean and renewable energy source, is a promising substitute for fossil fuels. Electricity-driven water electrolysis is an attractive pathway for clean hydrogen production. Accordingly, the development of electrolysis cells has drawn researchers’ attention to capital costs related to noble catalyst reduction and membrane degradation by the contaminations. In the literature, polymer electrolyte membranes (PEMs) have been studied on single cations contamination. In this study, we investigated the performance of a PEM on monovalent and divalent cation contamination by feed water. Artificial river water, called soft water, was used to analyze the effect of impurities on the PEM. The results demonstrated that the operating voltage drastically increased and induced cell failure with increasing Mg2+ and Ca2+ concentrations; however, it did not increase for Na+ and K+ after increase in voltage. Therefore, divalent cations have a stronger affinity than monovalent cations to degrade PEM and should be effectively excluded from the feed water.
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Development of High-Efficiency Solar Cell Modules for Photovoltaic-Powered Vehicles Reviewed International coauthorship
Yamaguchi M., Ozaki R., Nakamura K., Lee K.H., Kojima N., Ohshita Y., Masuda T., Okumura K., Satou A., Nakado T., Yamada K., Araki K., Ota Y., Nishioka K., Takamoto T., Zushi Y., Tanimoto T., Thiel C., Tsakalidis A., Jäger-Waldau A.
Solar RRL 6 ( 5 ) 2100429 2022.5
Language：English Publishing type：Research paper (scientific journal) Publisher：Solar RRL
Photovoltaic (PV)-powered vehicles are expected to play a critical role in a future carbon neutral society because it has been reported that the onboard PVs have great ability to reduce CO2 emission from the transport sector. Although the demonstration car with a III−V-based solar cell module has shown the PV-powered driving range of 36.6 km day−1 at solar irradiance of 6.2 kWh m−2 day−1, practical driving ranges of PV-powered vehicles are shown to be lower than estimated values due to some losses such as nonradiative recombination and resistance losses of solar cell modules under sunshine condition. This article presents analytical results for the effects of illumination intensity properties of various solar cell modules on the PV-powered driving range to develop highly efficient solar cell modules for vehicle-integrated applications. The analysis shows that improvements in shunt resistance and saturation current density of solar cell modules are necessary to improve illumination intensity properties of solar cell modules under low intensity sunshine condition. The calculations show that the III−V-based 3-junction solar cell modules with an efficiency of more than 30% have a potential PV-powered driving range of 30 km/day average and more than 50 km day−1 on a clear day.
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Effects of Agrivoltaics (Photovoltaic Power Generation Facilities on Farmland) on Growing Condition and Yield of Komatsuna, Mizuna, Kabu, and Spinach Reviewed
KIRIMURA Masaaki, TAKESHITA Shinichi, MATSUO Mitsuhiro, ZUSHI Kazufumi, GEJIMA Yoshinori, HONSHO Chitose, NAGAOKA Akira, NISHIOKA Kensuke
Ｅｎｖｉｒｏｎｍｅｎｔ Ｃｏｎｔｒｏｌ ｉｎ Ｂｉｏｌｏｇｙ 60 ( 2 ) 117 - 127 2022.4
Language：English Publishing type：Research paper (scientific journal) Publisher：日本生物環境工学会
In a sustainable society, it is necessary to develop systems that produce enough food and energy while also preserving the environment. Both agricultural production for food generation and photovoltaics for renewable energy production require large, open fields. In this research study, we investigate the feasibility of combining food and energy production into a single field by examining the effects of installing photovoltaic equipment above land used for farming. We grew komatsuna, kabu, mizuna, and spinach underneath photovoltaic equipment, and investigated the influence of shading from the photovoltaic equipment on plant growth and yields during winter cultivation. As expected, both the amount of solar radiation and the air and soil temperature were lower under the photovoltaics than those under the open field. The growth rate of komatsuna, kabu, and mizuna were slower. However, yields and qualities sufficient to meet market demands remained possible with extension of the cultivation periods. Therefore, although temperature and solar radiation are reduced under the photovoltaic equipment in winter, it is nevertheless possible to produce vegetables in the farmland, providing a novel opportunity to realize an integrated agricultural system with parallel production of food and energy.
DOI： 10.2525/ecb.60.117
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Chimney-ladder sulfide Sr9Ti8S24 as a thermoelectric material with low thermal conductivity Reviewed
Kamimizutaru K., Nagaoka A., Shigeeda Y., Nishioka K., Higashi T., Yasui S., Yoshino K.
Journal of Physics and Chemistry of Solids 163 2022.4
Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Physics and Chemistry of Solids
Chimney-ladder sulfide Sr9Ti8S24 (STS) has potential as a thermoelectric (TE) material because of its intrinsic low thermal conductivity. We studied the growth of a polycrystalline STS sample and its fundamental TE properties. The resistivity of n-type polycrystalline STS can be described as thermal activation and the potential barrier at grain boundary. Regarding the TE properties, n-type STS polycrystalline samples exhibit a low thermal conductivity <1 W/mK between 323 and 673 K caused by a large unit cell with an axis = 12.15 Å, c axis = 42.32 Å, and Umklapp scattering. Consequently, the figure of merit for the STS sample reaches 3.0 × 10−4 at 673 K.
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Ota Y., Araki K., Nagaoka A., Nishioka K.
Cleaner Engineering and Technology 7 2022.4
Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Cleaner Engineering and Technology
By mounting photovoltaics (PV) on the roof of an electric vehicle (EV), solar energy can be used to supply a considerable portion of the energy demand of the EV. The roof is the best place for PV installation on the vehicle body because doors and engine hood have less yearly-average sunlight available and more stringent mechanical requirements. The roof of a modern passenger vehicle such as a sedan is not flat, and parts with high curvature or a significant slope do not need to be covered. However, there are no design rules available for mounting PV on a vehicle roof, such as determining the coverage ratio. In this study, the distributions of roof shapes and sizes were obtained from trace drawings of various commercially available passenger vehicles. This was then used to calculate the distributions of the mechanical (i.e., local curvature) and optical (i.e., local solar utilization rate) properties. Based on the results, general guidelines were developed, including a potential coverage ratio of 96% for a hemispherical roof with a radius of curvature of 1 m. These guidelines have already been successfully demonstrated and prototyped with a small module.
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Impact of climatic conditions on prospects for integrated photovoltaics in electric vehicles Reviewed International coauthorship
Thiel C., Gracia Amillo A., Tansini A., Tsakalidis A., Fontaras G., Dunlop E., Taylor N., Jäger-Waldau A., Araki K., Nishioka K., Ota Y., Yamaguchi M.
Renewable and Sustainable Energy Reviews 158 2022.4
Language：English Publishing type：Research paper (scientific journal) Publisher：Renewable and Sustainable Energy Reviews
Integrated photovoltaics are an emerging technology which can extend the range of electric vehicles. However, up to now there is a lack of a consensus method that would provide consumers with an estimate of the fraction of annual driving which could be covered by solar power generated onboard in different usage scenarios and locations. To address this, we assess the energy implications of vehicle integrated photovoltaics for a commuter car and light delivery van for six climatic regions and for typical daily usage profiles over a ten-year period. The analysis captures the energy needs for driving and cabin temperature control to an unprecedented level of detail. Our results reveal that the grid power needed to drive such vehicles on identical routes can vary by more than 44% between climate regions. In the best case the solar power generated can cover up to 35% of the driving range per year. This contribution can vary by a factor of 2.5 between different climates, from 1800 to 5100 km annually, considerably mitigating the effect of ambient conditions on electric range. We propose developing consumer labels for solar electric vehicles that would consider this variation according to climatic conditions. The method described in this paper could help to frame initial discussions for such labels. We identify further requirements for research and development, standardisation, and policy needs.
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Impact and recent approaches of high-efficiency solar cell modules for PV-powered vehicles Reviewed
Masafumi Yamaguchi, Taizo Masuda, Kenji Araki, Yasuyuki Ota, and Kensuke Nishioka
Japanese Journal of Applied Physics 61 SC0802 2022.3
Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Physics and Chemistry of Solids
Chimney-ladder sulfide Sr9Ti8S24 (STS) has potential as a thermoelectric (TE) material because of its intrinsic low thermal conductivity. We studied the growth of a polycrystalline STS sample and its fundamental TE properties. The resistivity of n-type polycrystalline STS can be described as thermal activation and the potential barrier at grain boundary. Regarding the TE properties, n-type STS polycrystalline samples exhibit a low thermal conductivity <1 W/mK between 323 and 673 K caused by a large unit cell with an axis = 12.15 Å, c axis = 42.32 Å, and Umklapp scattering. Consequently, the figure of merit for the STS sample reaches 3.0 × 10−4 at 673 K.
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Curve correction of vehicle-integrated photovoltaics using statistics on commercial car bodies Reviewed
Ota Y., Araki K., Nagaoka A., Nishioka K.
Progress in Photovoltaics: Research and Applications 30 ( 2 ) 152 - 163 2022.2
Language：English Publishing type：Research paper (scientific journal) Publisher：Progress in Photovoltaics: Research and Applications
Typically, car roofs are curved, which means that vehicle-integrated photovoltaics (VIPVs) are also curved along the roof surface. The performance of the PV module is influenced by the local cosine loss and self-shadowing loss due to the curved surface. The ratio between the solar irradiances of curved and flat surfaces is defined as the curve correction factor, and it widely varies with the shape of the curved surface. When the curve correction factor is less than unity, the PV on a curved car roof performs worse than the PV on a flat plate. Understanding the typical range of the curve correction factor is important for the estimation of the energy generated by VIPV. We investigated the curved shapes of 100 lines of cars and 200 cases. The curved shapes were then used to extract eight nondimensional geometric parameters, and the distributions and correlations among the parameters were investigated. The parent population of the curved surfaces was estimated via a Monte Carlo simulation based on an analysis of the statistical characteristics. The distribution of curve correction factors for the car population was calculated via differential geometry weighted by the distribution of incident angles of sunlight (direct and diffused) affected by shading along the streets, which was obtained from 1 year of driving data for Miyazaki City, Japan. The curve correction factors were highly skewed, but the average value was 0.92. This means that VIPV requires a 10% boost in performance to compensate for the inherent loss due to the geometry of curved roofs.
DOI： 10.1002/pip.3473
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Shigeeda Y., Nagaoka A., Yoshino K., Nishioka K.
Journal of Physics and Chemistry of Solids 161 2022.2
Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Physics and Chemistry of Solids
We investigated the growth mechanism and the thermoelectric (TE) properties of the II-IV-V2 group chalcopyrite ZnSnSb2 with a pseudocubic structure, which is a key strategy for improving the TE performance by increasing the degeneracy at the valence band edge. The growth mechanism of ZnSnSb2 shows the peritectic reaction as: ZnSb + SnSb + liquid phase ↔ ZnSnSb2 for 320–360 °C. The ZnSnSb2 single phase was obtained from the starting composition of Zn:Sn:Sb = 1:5:2. The high-temperature TE properties were measured up to 573 K, and the thermal conductivity values were 1.5 times lower than the reported value, which was caused by enhanced phonon scattering by the off-stoichiometric composition. Consequently, the TE figure of merit for off-stoichiometric ZnSnSb2 reached 0.12 at 573 K, which is 1.4 times higher than that of the reported stoichiometric sample.
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Maeda M., Nagaoka A., Araki K., Nishioka K.
Solar Energy 231 243 - 251 2022.1
Authorship：Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Solar Energy
A precise and practical power generation forecasting method for outdoor photovoltaic (PV) arrays and its performance evaluation are essential for advancements in solar power generation. Specifically, accurate temperature measurements of each of the PV modules in an array, the entire outdoor PV array, and the power generation system are crucial regardless of climatic and irradiance conditions. However, outdoor PV temperatures are often affected by environmental factors, such as wind direction, wind speed, solar irradiance, and outdoor air temperature fluctuations. Hence, the temperature data vary greatly depending on the measurement point of the module, which is affected by the above environmental factors. The variations of and uncertainties in temperature often extend over long arrays of PV modules common to large-scale PV systems. Therefore, it is necessary to establish a straightforward and reproducible inspection method to determine a single and robust representative PV module temperature for an array. In this study, we have established one such inspection method for outdoor PV arrays. It was observed that the temperature at the center of the array was closest to the average temperature regardless of the measurement period and climatic conditions; thus, it can be considered as the unbiased and robust representative temperature for the PV array. Moreover, lower irradiance conditions are better for accurate and repeatable PV module temperature measurements. The mean temperature differences of the PV array from its average measured at the center of the array were 0.2 °C for low irradiance and 0.5 °C for high irradiance. The temperature difference observed will have 0.1% to 0.2% impact on the power estimation for monitoring purposes.
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Akira Nagaoka, Yusuke Shigeeda, Kensuke Nishioka, Taizo Masuda, and Kenji Yoshino
High Temperature Materials and Processes 40 439 - 445 2021.12
Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Physics and Chemistry of Solids
Chimney-ladder sulfide Sr9Ti8S24 (STS) has potential as a thermoelectric (TE) material because of its intrinsic low thermal conductivity. We studied the growth of a polycrystalline STS sample and its fundamental TE properties. The resistivity of n-type polycrystalline STS can be described as thermal activation and the potential barrier at grain boundary. Regarding the TE properties, n-type STS polycrystalline samples exhibit a low thermal conductivity <1 W/mK between 323 and 673 K caused by a large unit cell with an axis = 12.15 Å, c axis = 42.32 Å, and Umklapp scattering. Consequently, the figure of merit for the STS sample reaches 3.0 × 10−4 at 673 K.
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Analysis of temperature coefficients and their effect on efficiency of solar cell modules for photovoltaics-powered vehicles Reviewed International coauthorship
Yamaguchi M., Masuda T., Araki K., Ota Y., Nishioka K., Takamoto T., Thiel C., Tsakalidis A., Jaeger-Waldau A., Okumura K., Satou A., Nakado T., Yamada K., Zushi Y., Tanimoto T., Nakamura K., Ozaki R., Kojima N., Ohshita Y.
Journal of Physics D: Applied Physics 54 ( 50 ) 2021.12
Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Physics D: Applied Physics
Development of vehicles that are powered by photovoltaics (PV) is desirable, and is crucial for reduction in CO2 emissions from the transport sector to realize a decarbonized society. Our investigations show that the majority of the passenger cars that cruise only with solar energy can be realized by installing a high-efficiency PV module. Although the Toyota Prius demonstration car, which is equipped with a 860 W rated-output power PV module, has shown a 36.6 km d-1 PV-powered driving range at solar irradiance of 6.2 kWh m-2 d-1, practical driving ranges of PV-powered vehicles are shown to be shorter than the estimated values due to some losses of solar cell modules, such as temperature rise under sunny conditions. In this paper, we conduct a systematic analysis of the effects of these losses on the PV-powered driving range in order to obtain guidelines for the development of highly efficient solar cell modules for vehicle integrated applications. The analytical results show that the III-V compound solar cell modules have more suitable properties compared to other cells because of their higher potential conversion efficiencies of 37% with a smaller temperature coefficient of -0.19% C-1 compared to -0.29% C-1 for Si back contact solar cell modules and -0.26% C-1 for Si heterojunction solar cell modules. Our theoretical calculations that take these losses into account suggest that installing the III-V-based triple-junction solar cell modules provides a potential PV-powered driving range of 30 km d-1 on average, and more than 50 km d-1 on a sunny day under the irradiation conditions in Japan.
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Evaluating the Output of a Car-Mounted Photovoltaic Module under Driving Conditions Reviewed
Ota Y., Araki K., Nagaoka A., Nishioka K.
IEEE Journal of Photovoltaics 11 ( 5 ) 1299 - 1304 2021.9
Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Journal of Photovoltaics
In this article, we measured and estimated the outputs of car-mounted PV panels under actual driving conditions and different effective shading angles. On a sunny day, the performance ratio (PR) decreased to 0.99, despite the decrease in module temperature caused by the increased wind speed when driving. The PR decreased because of the effect of partial shading over the PV module. Public infrastructure could have led to dynamic partial shading passing across the PV module at high speeds. Furthermore, the effective shading angle being close to the sun's altitude could also have led to static partial shading. In contrast, on an overcast day the PR value was almost the same ($>$1) under both driving and parking conditions; this was because of the low module temperature and the spectrum effect.
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Wai S.H., Ota Y., Nishioka K.
International Journal of Hydrogen Energy 46 ( 53 ) 26801 - 26808 2021.8
Language：English Publishing type：Research paper (scientific journal) Publisher：International Journal of Hydrogen Energy
Synthetic methane is a major energy carrier having high energy density and can potentially replace fossil fuels. In this study, a solar-to-gas conversion system was developed using CO2 and solar-based hydrogen to meet the present energy demands. However, high reaction temperature induced by the inlet reactant gases can affect catalyst performance and cost of investment. Thus, we investigated power consumption of the reactor operating temperature for the system. The influence of hydrogen generation rates (GRH2) on the Sabatier reaction was analyzed, and the concentration of methane and total power consumption of the methanation system was highlighted. The highest methane concentrations were observed at 0.337 and 0.449 NL/min of GRH2. Subsequently, high methane composition (98.4%) was observed at 220 °C and 0.449 NL/min of GRH2. Therefore, methanation system with solar-based hydrogen can effectively distribute synthetic methane to the gas grid.
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Nagaoka A., Ota Y., Sakai K., Araki K., Matsuo H., Kadota N., Maeda K., Nakajima A., Nishioka K.
Renewable Energy 174 147 - 156 2021.8
Authorship：Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Renewable Energy
The concept of zero-energy building (ZEB) has attracted global attention in recent years as it involves offsetting the primary energy usage of a building on an annual base by the energy generated from renewable resources. The performance of wall-mounted photovoltaics (PV) for building applications has great potential for ZEB. In this study, we compared wall-mounted and common roof-mounted PV systems using a combination of experimental and theoretical studies. The wall-mounted PV system exhibited an unusual performance behavior depending on the season. Winter is a suitable season for energy production from the wall-mounted PV system because of the low solar altitude and resulting lower incident angle of the sun. However, the performance ratio (PR) had twin peaks throughout the day that could not be explained by the classical model that uses irradiance and temperature variation. In summer, there was less irradiance on the vertical wall and the PR had triple peaks that were also hard to explain using the conventional model. We established a detailed output power model of the wall-mounted PV using spectrum variation on a vertical plane. Our approach is the development of spectrum model that can be applied to all-climate and computed the performance variation according to the sun's orientation and incident angle. Our model quantitatively explains unique seasonal and daily efficiency variations for the wall-mounted PV system (twin peaks in winter and triple peaks in summer). Our validated model can be utilized to map a suitable location for a wall-mounted PV system.
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Nagaoka A., Yoshino K., Masuda T., Sparks T.D., Scarpulla M.A., Nishioka K.
Journal of Materials Chemistry A 9 ( 28 ) 15595 - 15604 2021.7
Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Materials Chemistry A
Thermoelectrics (TEs) are an important class of technology that harvest electric power directly from heat sources. When designing both high performance and environmentally friendly TE materials, the pseudo-cubic structure has great theoretical potential to maximize the dimensionless figure of meritZT. The TE multinary single crystal with a pseudo-cubic structure paves a new path toward manipulating valley degeneracy and anisotropy with low thermal conductivity caused by short-range lattice distortion. Here, we report a record highZT= 1.6 around 800 K realized in a totally environmentally benign p-type Na-doped Cu2ZnSnS4(CZTS) single crystal. The exceptional performance comes from a high power factor while maintaining intrinsically low thermal conductivity. The combination of the pseudo-cubic structure and intrinsic properties of the CZTS single crystal takes advantage of simple material tuning without complex techniques.
DOI： 10.1039/d1ta02978a
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Importance of Developing Photovoltaics-Powered Vehicles Reviewed
Masafumi Yamaguchi, Taizo Masuda, Takashi Nakado, Yusuke Zushi, Kenji Araki, Tatsuya Takamoto, Kenichi Okumura, Akinori Satou, Kazumi Yamada, Yasuyuki Ota, Kensuke Nishioka, Tsutomu Tanimoto, Kyotaro Nakamura, Ryo Ozaki, Nobuaki Kojima, Yoshio Ohshita
Energy and Power Engineering 13 147 - 162 2021.5
Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Physics and Chemistry of Solids
Chimney-ladder sulfide Sr9Ti8S24 (STS) has potential as a thermoelectric (TE) material because of its intrinsic low thermal conductivity. We studied the growth of a polycrystalline STS sample and its fundamental TE properties. The resistivity of n-type polycrystalline STS can be described as thermal activation and the potential barrier at grain boundary. Regarding the TE properties, n-type STS polycrystalline samples exhibit a low thermal conductivity <1 W/mK between 323 and 673 K caused by a large unit cell with an axis = 12.15 Å, c axis = 42.32 Å, and Umklapp scattering. Consequently, the figure of merit for the STS sample reaches 3.0 × 10−4 at 673 K.
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Phase diagram of the Ag2SnS3–ZnS pseudobinary system for Ag2ZnSnS4 crystal growth Reviewed
Nagaoka A., Yoshino K., Kakimoto K., Nishioka K.
Journal of Crystal Growth 555 125967 2021.2
Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Crystal Growth
The phase equilibrium of the Ag SnS –ZnS pseudobinary system for the growth of Ag ZnSnS (AZTS) crystals was investigated using the equilibration-quenching technique. The growth mechanism of AZTS follows the peritectic reaction liquid phase + ZnS phase ↔ AZTS phase, which occurs at a composition of ~20 mol% ZnS and a temperature of approximately 700 °C. The AZTS polycrystalline sample was obtained from the stoichiometric melt growth. The kesterite structure of the AZTS sample without secondary phases was identified by a combination of X-ray diffraction and Raman spectroscopy measurements. The electron carrier concentration and conductivity, determined by the Hall effect measurement, were (3.0–6.3) × 10 cm and (5.6–9.2) × 10 S/cm, respectively. The slightly Zn-rich and S-poor composition led to n-type conduction in the AZTS because of the dominant Zn antisites on Ag (Zn ) and S vacancy (V ) defects. Therefore, this study can make a significant contribution to the research and application of AZTS materials. 2 3 2 4 Ag S 15 −3 −4
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Development of High-Efficiency Solar Cell Modules for Photovoltaic-Powered Vehicles Reviewed
Yamaguchi M., Ozaki R., Nakamura K., Lee K.H., Kojima N., Ohshita Y., Masuda T., Okumura K., Satou A., Nakado T., Yamada K., Araki K., Ota Y., Nishioka K., Takamoto T., Zushi Y., Tanimoto T., Thiel C., Tsakalidis A., Jäger-Waldau A.
Solar RRL 2021
Language：English Publishing type：Research paper (scientific journal) Publisher：Solar RRL
Photovoltaic (PV)-powered vehicles are expected to play a critical role in a future carbon neutral society because it has been reported that the onboard PVs have great ability to reduce CO2 emission from the transport sector. Although the demonstration car with a III−V-based solar cell module has shown the PV-powered driving range of 36.6 km day−1 at solar irradiance of 6.2 kWh m−2 day−1, practical driving ranges of PV-powered vehicles are shown to be lower than estimated values due to some losses such as nonradiative recombination and resistance losses of solar cell modules under sunshine condition. This article presents analytical results for the effects of illumination intensity properties of various solar cell modules on the PV-powered driving range to develop highly efficient solar cell modules for vehicle-integrated applications. The analysis shows that improvements in shunt resistance and saturation current density of solar cell modules are necessary to improve illumination intensity properties of solar cell modules under low intensity sunshine condition. The calculations show that the III−V-based 3-junction solar cell modules with an efficiency of more than 30% have a potential PV-powered driving range of 30 km/day average and more than 50 km day−1 on a clear day.
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Chalcostibite Single-Crystal CuSbS<sub>2</sub> as High-Performance Thermoelectric Material Reviewed
Nagaoka Akira, Takeuchi Manato, Shigeeda Yusuke, Kamimizutaru Koki, Yoshino Kenji, Nishioka Kensuke
MATERIALS TRANSACTIONS 61 2407 - 2411 2020.12
Language：English Publishing type：Research paper (scientific journal) Publisher：公益社団法人 日本金属学会
Chalcostibite CuSbS<sub>2</sub> has attracted attention as an environmentally friendly material in thermoelectric (TE) field. Our investigations into the TE properties of high-quality p-type CuSbS<sub>2</sub> single crystals revealed that they exhibit a uniquely low thermal conductivity caused by the active lone-pair electrons in Sb<sup>3+</sup> ions. The electrical conductivity was improved by the high density of shallow acceptor Cu vacancies and the absence of potential barriers to carrier transport. Consequently, the figure of merit for the Cu-poor CuSbS<sub>2</sub> single crystal reached 0.5 at 700 K, which is 25 times higher than that of the reported polycrystalline sample.
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Hishikawa Y., Higa M., Takenouchi T., Ueda Y., Nishioka K., Kobayashi T., Minemoto T., Taniguchi H., Wakabayashi H., Yoshita M.
Solar Energy 211 82 - 89 2020.11
Language：English Publishing type：Research paper (scientific journal) Publisher：Solar Energy
© 2020 Highly precise outdoor current-voltage (I-V) curve measurement of crystalline silicon photovoltaic (PV) modules has been achieved, by monitoring the solar irradiance with a PV module irradiance sensor (PVMS), measuring the curves in 0.2–0.5 s, and filtering out the data affected by spatial nonuniformity of irradiance. The I-V curves were corrected for temperature by using a recently developed translation formula. Good reproducibility in the short circuit current ISC, open circuit voltage VOC, and maximum power Pmax measurements was confirmed, based on repeated measurements for one week. Small values of relative standard deviation σ, i.e., 0.1–0.23% and 0.24–0.42% for the ISC/GPVMS and Pmax/GPVMS, respectively, were confirmed even on partially sunny days and cloudy days when the solar irradiance is very unstable. Here, GPVMS denotes the irradiance measured by using a PVMS. The values of σ for various kinds of commercial crystalline silicon modules, including the p-type BSF, p-type PERC, n-type backside contact and silicon heterojunction, were also investigated in longer periods including different seasons of the year, which were 0.1–0.5% and 0.5–1.3% in the irradiance ranges of 0.9–1.1 kW/m2 and 0.3–0.5 kW/m2, respectively. The results have demonstrated that precise outdoor I-V curve measurements are possible in wide range of irradiance under various weather conditions. They are useful for improving the throughput and accuracy of onsite I-V measurements in operation and maintenance. Possible sources of residual measurement error and methods to further improve the precision are also discussed.
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How did the knowledge of CPV contribute to the standardization activity of VIPV? Reviewed
Araki K., Ji L., Kelly G., van der Ham A., Agudo E., Antón I., Baudrit M., Carr A., Herrero R., Kurtz S., Liu Z., Pravettoni M., Ota Y., Tobita H., Yoon S., Yoshita M., Yamaguchi M., Nishioka K.
AIP Conference Proceedings 2298 2020.11
Language：English Publishing type：Research paper (scientific journal) Publisher：AIP Conference Proceedings
The standardization of VIPV (Vehicle-integrated photovoltaic) has been driven by the international discussion among scientists and engineers, from photovoltaic research, photovoltaic industries, automobile and other industries, and testing laboratories. Since the VIPV is not flat and fixed installation, as well as a wide variety of designs, the knowledge of CPV (Concentrator Photovoltaic) technology, has been useful for developing testing technologies. This paper took two examples in the performance testing and the test for the tolerance for the partial/dynamic shading, utilizing various techniques exclusively used in CPV technologies.
DOI： 10.1063/5.0032997
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Araki K., Ota Y., Saiki H., Tawa H., Nishioka K., Sato D., Yamaguchi M.
AIP Conference Proceedings 2298 2020.11
Language：English Publishing type：Research paper (scientific journal) Publisher：AIP Conference Proceedings
The performance of CPV is sensitive to the spectrum change. Several previous works have been published on the sensitivity of multi-junction cells to airmass variations as well as works on band gap tuning and optimization of multi-junction stacks under concentrated radiation in various locations. Such a variety of atmospheric conditions, airmass as well as climate (quality of direct sunlight) are dynamic and cannot be controlled by the product design. All we can do is to customize the design by locations (not capable of dynamic variation) or inventing a robust device configuration against a dynamic change of atmospheric conditions (also effective to regional variation). Enhancing a luminescent coupling is useful to suppress the spectrum mismatching loss inherent to outdoor CPV installation. The configuration of the solar cell with 100 % of the recycling of the surplus photon energy for compensating spectrum mismatching is called an SMJ solar cell (super-multi-junction solar cell). The advantage of the SMJ solar cells in non-concentrating fixed sloped angle installation was intensively analyzed in the previous works. However, that of CPV was only investigated under the combination of the worst-case atmospheric parameter distributions, and not under the realistic spectrum variations, so that the calculation result was too extreme. This paper intended to fill the missing stone, by updating a previous result on CPV modeled under the combination of the worst-case variations of atmospheric conditions in the worst locations for CPV, by the realistic fluctuation pattern of meteorological parameters and climate using the intensive analysis that was done to the non-concentration installation (fixed installation). The SMJ was also confirmed valid to CPV under the dynamic fluctuation of the direct solar resources. Different from the non-concentrating operation, the normal CPV was found raising annual average outdoor efficiency under realistic atmospheric conditions simulated by the regional states in Miyazaki, Japan, up to six-junctions. This analysis also implies the bandgap design guideline for the robustness of the spectrum variation, trying to place the bandgap energy of the some of the sub-cells close to the water-absorption band (1.3 eV, 1.1 eV, and 0.89 eV).
DOI： 10.1063/5.0032996
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Nagaoka A., Nishioka K., Yoshino K., Kuciauskas D., Scarpulla M.A.
Journal of Electronic Materials 2020.8
Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Electronic Materials
© 2020, The Minerals, Metals & Materials Society. The photovoltaic performance of CdTe solar cells is mainly limited by low doping and short minority carrier lifetime. Group-V element doping and Se-alloying have a significant impact on tuning these fundamental CdTe properties. In this paper, we report the growth of p-type As-doped, Cd-rich CdTe1−xSex single crystals using metallic Cd as the solvent in the traveling-heater method. The structural and electrical properties of CdTe1−xSex are examined for different Se concentrations. CdTe1−xSex single crystals (0 ≤ x ≤ 0.5) with zincblende structure indicate homogeneous composition. The 1017 cm−3 As-doping activation efficiency can be maintained at close to 50% for x ≤ 0.2. Se alloying leads to bulk minority carrier lifetime exceeding 30 ns for samples doped near 1017 cm−3. These results help us to overcome the current roadblocks in device performance.
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Wai S., Ota Y., Sugiyama M., Nishioka K.
Applied Sciences (Switzerland) 10 ( 9 ) 3144-1 - 3144-11 2020.5
Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Sciences (Switzerland)
© 2020 by the authors. Power to gas (P2G) process chains have tremendous potential to enhance energy systems because of the capability of solar energy to convert solar radiation into electrical energy as well as the increasing use of specific gases as a means to store the resulting energy. Utilizing sunlight, photovoltaic systems are capable of producing useful gases such as hydrogen (H2) and methane (CH4). These gases are utilized in gas grids, transportation, and heavy industry. In employing a sunlight-derived gas, H2 production, by water disbanding, needs to be cost-effective with tremendous adaptability. New powerful solar to gas conversion system modules have been successfully carried out in the University of Miyazaki, Japan. These systems contain DC/DC converters and electrolyzer sets linked in parallel with efficient three concentrator photovoltaics (CPV). The performance of the solar to methane conversion process and power consumption analysis will be the focus of the current research. Efficiencies of 97.6% of CO2 to CH4 conversion and 13.8% for solar to methane on a clear sunny day were obtained by utilizing highly efficient CPV modules connected with multiple converters, electrochemical cells, and reactors fixed with Ni-based catalysts.
DOI： 10.3390/app10093144
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Nagaoka A., Nishioka K., Yoshino K., Katsube R., Nose Y., Masuda T., Scarpulla M.A.
Applied Physics Letters 116 ( 13 ) 132102-1 - 132102-5 2020.4
Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Letters
© 2020 Author(s). Acceptor doping CdTe with group-V elements is promising for increasing the power conversion efficiency of CdTe photovoltaic devices via an increased hole concentration and open circuit voltage (VOC). In past work, we have investigated doping with As in Cd-rich CdTe single crystals grown using the Cd-solvent traveling heater method we have developed. In this study, we compare the doping parameters and stability of hole concentration in the light and dark for P, As, and Sb dopants in crystals cooled very slowly from the growth temperature to approximate thermal equilibrium. In contrast to older reports of a high acceptor ionization energy for Sb, our temperature dependent Hall effect experiments reveal an acceptor ionization energy slightly above 90 meV for Sb doping in the mid 1016 cm-3 range. Room temperature hole concentrations above 1016 cm-3 are observed for P, As, and Sb with each dopant type exhibiting only small changes in hole concentrations over 2 years' time at room temperature. Crystals doped with P, As, or Sb exhibit increased conductivity after above-gap illumination, which decays over periods of minutes to hours depending on temperature. Analysis of the photoconductivity decay reveals a barrier attributed to hole capture of 190-280 meV for the series P, As, and Sb.
DOI： 10.1063/5.0004883
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The outdoor field test and energy yield model of the four-terminal on si tandem PV module Reviewed
Araki K., Tawa H., Saiki H., Ota Y., Nishioka K., Yamaguchi M.
Applied Sciences (Switzerland) 10 ( 7 ) 2529-1 - 2529-17 2020.4
Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Sciences (Switzerland)
© 2020 by the authors. The outdoor field test of the 4-terminal on Si tandem photovoltaic module (specifically, InGaP/GaAs on Si) was investigated and a performance model, considering spectrum change affected by fluctuation of atmospheric parameters, was developed and validated. The 4-terminal on Si tandem photovoltaic module had about 40% advantage in seasonal performance loss compared with standard InGaP/GaAs/InGaAs 2-terminal tandem photovoltaic module. This advantage increases (subarctic zone < temperate zone < subtropical zone). The developed and validated model used an all-climate spectrum model and considered fluctuation of atmospheric parameters. It can be applied every type of on-Si tandem solar cells.
DOI： 10.3390/app10072529
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Tawa H., Saiki H., Ota Y., Araki K., Takamoto T., Nishioka K.
Applied Sciences (Switzerland) 10 ( 2 ) 703-1 - 703-15 2020.1
Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Sciences (Switzerland)
© 2020 by the authors. Because semiconductors absorb wavelengths dependent on the light absorption coefficient, photovoltaic (PV) energy output is affected by the solar spectrum. Therefore, it is necessary to consider the solar spectrum for highly accurate PV output estimation. Bird's model has been used as a general spectral model. However, atmospheric parameters such as aerosol optical depth and precipitable water have a constant value in the model that only applies to clear days. In this study, atmospheric parameters were extracted using the Bird's spectrum model from the measured global spectrum and the seasonal fluctuation of atmospheric parameters was examined. We propose an overcast spectrum model and calculate the all-weather solar spectrum from clear to overcast sky through linear combination. Three types of PV modules (fixed Si, two-axis tracking Si, and fixed InGaP/GaAs/InGaAs triple-junction solar cells) were installed at the University of Miyazaki. The estimated performance ratio (PR), which takes into account incident angle and spectral variations, was consistent with the measured PR. Finally, the energy yield of various PVs installed across Japan was successfully estimated.
DOI： 10.3390/app10020703
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Chantana J., Imai Y., Kawano Y., Hishikawa Y., Nishioka K., Minemoto T.
Renewable Energy 145 1317 - 1324 2020.1
Language：English Publishing type：Research paper (scientific journal) Publisher：Renewable Energy
© 2019 Elsevier Ltd Spectral grain and loss (spectral gain&loss) of several-type PV technologies (amorphous silicon (a-Si), perovskite (perov), CdTe, CuInSe2 (CIS), multi-crystalline silicon (mc-Si), single-crystalline silicon back-contact (BC), single-crystalline silicon (sc-Si), and heterostructure-with-intrinsic-thin-layer (HIT)) was investigated in different places (Kusatsu city, Tsukuba city, and Miyazaki city in Japan) in a year. Spectral gain&loss is defined as a ratio of short-circuit current (ISC) corrected by solar irradiance (Irr) for PV module at an average photon energy (APE) to its ISC under standard test condition. The blue-rich spectra with APE over 1.88 eV yield spectral gain (spectral gain&loss over 1) for CdTe, perov, and a-Si PV technologies owing to large band-gap energy (Eg) values of 1.47, 1.60, and 1.80 eV, respectively. On the other hand, red-rich spectra with APE below 1.88 eV lead to spectral gain for CIS, mc-Si, BC, sc-Si, and HIT PV technologies with smaller Eg values of 1.21, 1.13, 1.17, 1.16, and 1.09 eV, respectively. Moreover, since average APE values in Kusatsu city, Tsukuba city, and Miyazaki city are 1.931, 1.900, and 1.899 eV, respectively, a-Si, perov, and CdTe PV technologies are suitable in term of spectral response. The spectral gain&loss of PV modules compared with sc-Si PV module is moreover discussed.
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Araki K., Ota Y., Saiki H., Tawa H., Nishioka K., Yamaguchi M.
Applied Sciences (Switzerland) 9 ( 21 ) 4598-1 - 4598-21 2019.11
Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Sciences (Switzerland)
© 2019 by the authors. Licensee MDPI, Basel, Switzerland. The highest-efficiency solar cell in the efficiency race does not always give the best annual energy yield in real world solar conditions because the spectrum is always changing. The study of radiative coupling of concentrator solar cells implies that efficiency could increase by recycling the radiative recombination generated by the surplus current in the upper junction. Such a configuration is called a super-multi-junction cell. We expand the model in the concentrator solar cell to a non-concentrating installation. It is shown that this super-multi-junction cell configuration is robust and can keep maximum potential efficiency (50% in realistic spectrum fluctuation) for up to 10 junctions. The super-multi-junction cell is also robust in the bandgap engineering of each junction. Therefore, a future multi-junction may not be required for tuning the bandgap to match the standard solar spectrum, as well as relying upon artificial technologies such as epitaxial lift-off (ELO), wafer-bonding, mechanical-stacking, and reverse-growth, but merely uses upright and lattice-matching growth technologies. We present two challenging techniques; one is the optical cap layer that may be the directional photon coupling layer in the application of the photonics technologies, and another is the high-quality epitaxial growth with almost 100% radiative efficiency.
DOI： 10.3390/app9214598
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Reduction of Soiling on Photovoltaic Modules by a Tracker System with Downward-Facing Standby State Reviewed
Ota Y., Nagaoka A., Nishioka K.
International Journal of Photoenergy 2019 1296065-1 - 1296065-8 2019.10
Language：English Publishing type：Research paper (scientific journal) Publisher：International Journal of Photoenergy
© 2019 Yasuyuki Ota et al. The radiation received by solar cells within photovoltaic modules is lower than that arriving at the module surface. One of the causes of this energy loss is soiling of the module surface. Therefore, the influence of dust adhesion on photovoltaic modules must be studied. In this study, we prepared two tracker systems: a new system and a typical system. During the night, the former can switch to a downward-facing standby state, while the latter assumes an upward-facing standby state. The soiling on the polymethylmethacrylate and glass set on the tracker systems with both standby states was evaluated for 20 months in Miyazaki, Japan. By adopting the tracker system with the downward-facing standby state, a direct transmittance that was more-than-5% higher than before was consistently obtained at 500 nm in both cases with polymethylmethacrylate and glass.
DOI： 10.1155/2019/1296065
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Araki K., Ota Y., Lee K., Nishioka K., Yamaguchi M.
AIP Conference Proceedings 2149 2019.8
Language：English Publishing type：Research paper (international conference proceedings) Publisher：AIP Conference Proceedings
© 2019 American Institute of Physics Inc.. All rights reserved. It is well known that CPV is sensitive to the spectrum change, and its high-performance is often discouraged by the spectrum mismatching loss by the seasonal change of the atmospheric parameters. We found multiple methods could improve the robustness to the spectrum sensitivity, including enhancing luminescence coupling and fine-tuning to the bottom-bandgap matched to local atmospheric conditions (water absorption).
DOI： 10.1063/1.5124194
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Standardization of the CPV technology in 2019 - The path to new CPV technologies Reviewed
Araki K., Algora C., Siefer G., Nishioka K., Leutz R., Carter S., Wang S., Askins S., Ji L., Kelly G.
AIP Conference Proceedings 2149 2019.8
Language：English Publishing type：Research paper (international conference proceedings) Publisher：AIP Conference Proceedings
© 2019 American Institute of Physics Inc.. All rights reserved. CPV incorporates a wide variety of technologies and options. The application of these technologies, however, is not limited to CPV only. The basic approach of the standardization for CPV is thus expanding the scope to a broader range of technologies. The knowledge gained through our activities is contributing to standardizations in PV technologies like, e.g. standards for trackers. In this regard, the standardization activities for CPV is also moving to new fields of applications.
DOI： 10.1063/1.5124220
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Araki K., Ota Y., Lee K., Nishioka K., Yamaguchi M.
2019 18th International Conference on Optical Communications and Networks, ICOCN 2019 2019.8
Language：English Publishing type：Research paper (international conference proceedings) Publisher：2019 18th International Conference on Optical Communications and Networks, ICOCN 2019
© 2019 IEEE. It is known that multi-junction solar cells are sensitive to the spectrum change [1]-[2], and its high-performance is often discouraged by the spectrum mismatching loss by the seasonal change of the atmospheric parameters [3]-[4]. It implies that the highest efficiency solar cell in the standard testing condition does not always promise the most excellent annual energy yield in the real world solar condition that the spectrum is ever-changing. We found the ultimate solution of the seasonal loss will be autonomous compensation of the carrier imbalance by the radiative coupling among junctions due to radiative recombination [5]. We call it a super-multi-junction solar cell. The annual operation of the super-multi-junction solar cell was simulated by the validated operation model of the photovoltaic module using multi-junction solar cells. It was shown that the super-multi-junction architecture was found robust up to 6 junctions. The robust high-efficiency solar cell can be the right candidate of the vehicle-integrated photovoltaic that run a majority of electric vehicles on solar energy.
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Akira Nagaoka, Kensuke Nishioka, Kenji Yoshino, Darius Kuciauskas, and Michael A. Scarpulla
Applied Physics Express 12 ( 8 ) 081002-1 - 081002-5 2019.7
Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Express
© 2019 The Japan Society of Applied Physics. The combination of group-V element doping and Cd-rich composition is the most promising current strategy for maximizing p-type doping while preserving long lifetime. In this study, we carefully measure the equilibrium p-type doping limit for As-doped Cd-rich CdTe single crystals and demonstrate a doping limit in the low 1017 cm-3 range upon slow cooling. We present evidence for self-compensation with rapidly decreasing doping efficiency per added As above 5 × 1016 cm-3, yet we also demonstrate CdTe with >1017 cm-3 hole concentration and bulk lifetime >30 ns. Such crystals allow As-doped CdTe photovoltaic devices with open-circuit voltage exceeding 900 mV.
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Growth of CuSbS2 Single Crystal as an Environmentally Friendly Thermoelectric Material Reviewed
A. Nagaoka, M. Takeuchi, K. Yoshino, S. Ikeda, S. Yasui, T. Taniyama, and K. Nishioka
Physica Status Solidi (A) Applications and Materials Science 2019.2
Language：English Publishing type：Research paper (scientific journal)
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Long-Term Reliability Evaluation of Silica-Based Coating with Antireflection Effect for Photovoltaic Modules Reviewed
Nishioka K., Moe S., Ota Y.
Coatings 9 ( 1 ) 49 2019.1
Language：English Publishing type：Research paper (scientific journal)
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Araki K., Ota Y., Nishioka K., Tobita H., Ji L., Kelly G., Yamaguchi M.
2018 IEEE 7th World Conference on Photovoltaic Energy Conversion, WCPEC 2018 - A Joint Conference of 45th IEEE PVSC, 28th PVSEC and 34th EU PVSEC 368 - 373 2018.11
Language：English Publishing type：Research paper (scientific journal) Publisher：2018 IEEE 7th World Conference on Photovoltaic Energy Conversion, WCPEC 2018 - A Joint Conference of 45th IEEE PVSC, 28th PVSEC and 34th EU PVSEC
With the progress of the automotive technology, it will be possible that the most of the personal cars will be able to run by the solar energy equipped with high-efficiency and 3-D curved solar panels. The issue is the conventional IEC60904 international standard is based on a 2-D plane, and it is needed to expand to 3-D. Our attempt is trying to define 3-D sunshine irradiation and rating to the 3-D curved solar panels, using a newly introduced curve correction factor. This approach can be applied to the rating of the flexible PV modules. Another issue is the environmental test needed as a car-component. The required tests were compared to the typical testing conditions of PV.
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Influence of Wind Speed and Direction on Cooling Effect for Concentrator Photovoltaic Module Investigated Using Wind Tunnel Reviewed
Ahmad N., Nishioka K., Ota Y.
Recent Advances in Electrical & Electronic Engineering 11 ( 4 ) 407 - 410 2018.11
Language：English Publishing type：Research paper (scientific journal)
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Tsuji M., Rahman M., Hishikawa Y., Nishioka K., Minemoto T.
Solar Energy 173 89 - 96 2018.10
Language：English Publishing type：Research paper (scientific journal) Publisher：Solar Energy
© 2018 Elsevier Ltd The output energy yield from the photovoltaic (PV) module is influenced mainly by the spectral irradiance under outdoor conditions. To evaluate the effects upon PV modules, a quantitative index is essential for appropriate statistical analysis, because spectral irradiance distribution is a function of wavelength. Average photon energy (APE) is an index which represents a quantitative value of spectral irradiance distribution, and an APE value calculated from 350 to 1050 nm wavelength (APE350-1050) uniquely describes the shape of the solar spectrum at Kusatsu-city. Meanwhile, our previous study showed that APE has effects on PV performance, especially on short circuit current (ISC) of PV modules. Therefore, APE is a useful index of evaluation of PV performance under actual outdoor conditions. In Japan, the uniqueness of APE have been demonstrated at Ritsumeikan University in Kusatsu-city, Shiga prefecture as an index of spectral irradiance distribution and its effect on PV performance. However, the spectral characteristics in other regions of Japan with respect to Ritsumeikan University in Kusatsu-city are not yet clearly understood. This study aims to describe and discuss the uniqueness of solar spectrum obtained from three sites: Ritsumeikan University in Kusatsu-city, National Institute of Advanced Industrial Science and Technology in Tsukuba-city, and the University of Miyazaki in Miyazaki-city, Japan based on similar APE for standardization with respect to Kusatsu-city. In regard to this view, the coefficient of determination, denoted R2, was used to quantify the degree of coincidence for the shape of the solar spectrum. The results obtained from the R2 method were compared for evaluating consistency among three sites on the basis of Ritsumeikan University. It was found that the high R2 values of 0.988–0.998 correspond to small APE errors of 0.006–0.028 eV. These errors are raised from the different sites due to the slight variations in the shapes of the solar spectrum. For further evaluation of the influence of ISC of different PV modules, spectral mismatch correction factor (MM) based on the irradiance obtained from a pyranometer as a function of APE is examined and compared with three sites using similar APE. Results showed that the MM of the PV modules which have spectral sensitivities in the long wavelength band is approximately 1 regardless of the APE, except for cadmium telluride (CdTe) PV module. We thus conclude that the ISC of different PV modules except the CdTe PV module have uniqueness, if the irradiance and APE350-1050 measured from all three sites are similar.
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Analysis of fluctuation of atmospheric parameters and its impact on performance of CPV Reviewed
Araki K., Ota Y., Lee K.H., Sakai T., Nishioka K., Yamaguchi M.
AIP Conference Proceedings 2012 2018.9
Language：English Publishing type：Research paper (scientific journal) Publisher：AIP Conference Proceedings
The measurement of the atmospheric parameters by fitting to the measured spectrum was used to analyze the uncertainty of the energy generation of CPV. It was found the fluctuation of the atmospheric parameters substantially impact to the energy yield of multi-junction cells. The calculation considering the variation of atmospheric parameters showed a dramatic decline of the annual energy yield from the cells with more than five junctions. Optimized multijunction solar cells using luminescent coupling for an adjuster of the spectrum mismatching was proposed and analyzed. The top and the bottom junctions have lower bandgap for buffering to the mismatching and collecting a full range of the sunlight by robust energy conversion, and the annual energy substantially increases even by five or six junctions. The advanced modeling of the multi-junction cells considering the sensitivity of the atmospheric parameters and the degree of luminescent coupling is useful to the accurate prediction of the solar power in the smart control to the car-roof PV.
DOI： 10.1063/1.5053530
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Standardization of the CPV and car-roof PV technology in 2018 - Where are we going to go? Reviewed
Araki K., Algora C., Siefer G., Nishioka K., Leutz R., Carter S., Wang S., Askins S., Ji L., Kelly G.
AIP Conference Proceedings 2012 2018.9
Language：English Publishing type：Research paper (scientific journal) Publisher：AIP Conference Proceedings
The work of IEC TC82 WG7 aims for the standardization of concentrator modules, and their optics, mechanics and other advanced photovoltaic systems. These standards will be in the general areas of safety, photoelectric performance and environmental reliability tests. The standards ultimately produced should be universal and non-restrictive in their application, taking into account different environments and manufacturing technologies. In addition to the essential electrical and mechanical characteristics, standards will be written for other important factors such as thermal performance, high voltage performance, angular performance, mechanical precision, specific testing fault resistance and fault-tolerant design. Recently an expanded group started to discuss standardization of the car-roof PV.
DOI： 10.1063/1.5053527
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Nakamura S., Iwamura E., Ota Y., Nishioka K.
AIMS Materials Science 5 ( 4 ) 756 - 769 2018.8
Language：English Publishing type：Research paper (scientific journal) Publisher：AIMS Materials Science
© 2018, the Author(s). Heat dissipation for electronic devices has attracted extensive interest because the reliability, lifetime, and performance are seriously affected by temperature increases during the operation. The effects of inorganic fillers in heat dissipation coatings on the temperature reduction of heat sources between 310 and 400 K were investigated. Acrylic coating films with calcium fluoride, pyrolytic boron nitride, and silicon carbide particle fillers were formed on pristine aluminum plates that were then heated in a closed system. A significant temperature reduction of about 17 K was obtained at the surface of a heat source with an acrylic coating film including calcium fluoride particles on the aluminum plate; under equivalent conditions, the uncoated aluminum plate temperature reached 373 K. The materials used in the coatings were characterized by wavelength-dependent infrared absorption and emission properties. Although the overall emissivity in wide wavelength range is previously considered to be the most crucial variable in radiative cooling, materials have specific infrared absorption and emission properties depending on their physical structures. Therefore, elucidating the relationship between the characteristics of an individual heat emission material and its cooling effects is necessary in order to design more effective heat dissipation measures based on radiation. It was confirmed that the selection of an appropriate filler material with specific infrared emission properties corresponding to the emitting wavelength at the given temperature of the objects to be cooled was important. Distinctive radiative cooling effects were thus obtained, even in the relatively low-temperature range examined here, by the selection of appropriate materials with radiative properties in the temperature range of interest.
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Kawashima R., Sakai T., Ota Y., Nishioka K.
Japanese Journal of Applied Physics 57 ( 8 ) 2018.8
Language：English Publishing type：Research paper (scientific journal) Publisher：Institute of Physics
White foam glass produced from waste glass as raw material is attractive from the viewpoints of waste recycling, white color with high reflectance, and weed control. It is considered to have potential for increasing the power output of bifacial photovoltaic modules, primarily owing to enhanced light reflectance from the ground and also reduced operation and maintenance cost through effective weed control. In this study, we investigated the effect of white foam glass spread in the photovoltaic installation site by measuring the albedo factor and observing the growth of weeds that are known to create shadows over a period of time. An effective increase in albedo was observed after spreading the white foam glass. The transmittance of the white foam glass was very low and the sunlight did not reach the ground below it. Consequently, plant growth and photosynthesis were obstructed and the effect of weed control was observed.
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Ota Y., Ueda K., Takamoto T., Nishioka K.
Japanese Journal of Applied Physics 57 ( 8 ) 08RD08 2018.8
Language：English Publishing type：Research paper (scientific journal) Publisher：Institute of Physics
We discussed the outdoor operation of a fixed flat sub module with an InGaP/GaAs/InGaAs inverted metamorphic triple-junction solar cell (IMM module) for the first time in the world. The global solar spectrum distribution was assessed using the average photon energy (APE) and spectral matching ratio (SMR) indexes in this study. The conversion efficiency of the IMM module was more than 30% and was markedly affected by APE rather than by module temperature under real environmental conditions. [Formula: see text] markedly increased in the high APE region. In the case of APE of more than 1.60 eV, the photocurrent of the bottom subcell decreased owing to the blue-rich spectrum, which limited the short-circuit current. The absorption region of the bottom subcell overlapped with the water absorption region in the solar spectrum; therefore, environmental conditions such as water precipitation greatly affected the output of the current-matching inverted triple-junction solar cell.
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Nishioka K., Miyamura K., Ota Y., Akitomi M., Chiba Y., Masuda A.
Japanese Journal of Applied Physics 57 ( 8 ) 2018.8
Language：English Publishing type：Research paper (scientific journal) Publisher：Institute of Physics
There is a growing need for the precise outdoor performance measurement of photovoltaic (PV) modules for low-cost onsite performance measurement, monitoring, and failure diagnosis. For the precise evaluation of a PV module, an accurate temperature measurement technique is required. It is necessary to measure the temperature of the solar cell in a module structure (junction temperature) because it determines the temperature characteristics of the PV module, rather than the temperature of the backsheet. In this study, a PV module with an internal thermocouple was fabricated. A thermocouple was inserted immediately below the solar cell so that it could be in direct contact with the cell, enabling an accurate temperature measurement. Moreover, the temperature of the solar cell in the PV module structure was predicted by heat flux calculation using the backsheet temperature, which can be measured easily. In this manner, the solar cell temperature was estimated accurately within an error of ±1 °C.
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Evaluation and optimization of coating for wide acceptance angle concentrator photovoltaic module Reviewed
Ahmad N., Ota Y., Araki K., Lee K., Yamaguchi M., Nishioka K.
Japanese Journal of Applied Physics 57 ( 8S3 ) 08RD02-1 - 08RD02-5 2018.8
Language：English Publishing type：Research paper (scientific journal)
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Ota Y., Yamashita D., Nakao H., Yonezawa Y., Nakashima Y., Ebe H., Inagaki M., Mikami R., Abiko Y., Iwasaki T., Sugiyama M., Nishioka K.
Applied Physics Express 11 ( 7 ) 077101 2018.7
Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Express
© 2018 The Japan Society of Applied Physics. Using an optimized system comprising concentrator photovoltaic (CPV) modules, electrolyzers, and DC/DC converters for dynamic control, we achieved a one-day solar-to-hydrogen (STH) efficiency of 18.78%—the highest value for a sub-kilowatt-scale photovoltaic (PV) system under outdoor operation. We clarified that incorporating high-efficiency CPV modules and DC/DC converters in PV-driven solar hydrogen production systems is essential for obtaining the highest STH efficiency. Furthermore, we noted that the overpotential of electrochemical (EC) cells is a bottleneck for the improvement in STH efficiency; therefore, future work should focus on reducing such an overpotential.
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TOWARD STANDARDIZATION OF SOLAR TRACKERS, CONCENTRATOR PV, AND CAR-ROOF PV
Araki Kenji, Ji Liang, Kelly George, Algora Carlos, Siefer Gerald, NIshioka Kensuke, Muller Mathew, Leutz Ralf, Carter Sam, Wang Shitao, Askins Steve
グランド再生可能エネルギー国際会議論文集 1 ( 0 ) 2018
Language：English Publishing type：Research paper (scientific journal) Publisher：特定非営利活動法人 再生可能エネルギー協議会
IEC TC82 WG7 works for standardization of concentrator modules, and their optics, mechanics and other advanced photovoltaic systems. These standards will be in the general areas of safety, photoelectric performance and environmental reliability tests. The standards ultimately produced should be universal and non-restrictive in their application, taking into account different environments and manufacturing technologies. In addition to the essential electrical and mechanical characteristics, standards will be written for other relevant factors such as thermal performance, high voltage performance, angular performance, mechanical precision, specific testing fault resistance and fault-tolerant design. Recently an expanded group started to discuss standardization of the car-roof PV.
DOI： 10.24752/gre.1.0_37
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LONG TERM RELIABILITY OF ANTIREFLECTIVE SILICA-BASED COATING ON CIGS PHOTOVOLTAIC MODULE
Moe So Pyay, Ota Yasuyuki, Nishioka Kensuke
グランド再生可能エネルギー国際会議論文集 1 ( 0 ) 2018
Language：English Publishing type：Research paper (scientific journal) Publisher：特定非営利活動法人 再生可能エネルギー協議会
Photovoltaic (PV) module surfaces are suffered from dust deposition and reflection that can cause reduction in efficiency of PV. Therefore, the impact of reflection and soiling must be taken into account in PV performance. This study describes reliable surface coating with superhydrophilic properties that has no degradation on PV systems. We used nano-porous silica films with antireflective and anti-soiling effects on the surface of CIGS PV modules. The coating treatment was performed with single-layer coating on installed modules on Dec, 25 2014 and exposed outdoors to analyze the coating performance. The output of the array increased after coating than before coating. Besides, over 3 year‟s performance of antireflective coating was evaluated and we observed no degradation. Therefore, antireflective coating showed its long term effect of reliability on PV module surface.
DOI： 10.24752/gre.1.0_31
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Wai Soe Htet, Ota Yasuyuki, Yamashita Daiji, Sugiyama Masakazu, Nishioka Kensuke
グランド再生可能エネルギー国際会議論文集 1 ( 0 ) 2018
Language：English Publishing type：Research paper (scientific journal) Publisher：特定非営利活動法人 再生可能エネルギー協議会
In the future, power to gas process chain could play a vital role in the energy system because of long-term storage of solar energy and an effective transformation to usable gases. The resulted energy from the photovoltaic system can be transformed into useful gases such as hydrogen and methane which can be used in gas grids, auto-motives and industries. To use hydrogen as a useful, artificial, sunlight-derived gas, it is needed to achieve high efficiency and low cost production of hydrogen from sunlight irradiation by water splitting. A new effective solar to gas conversion system with multiple DC/DC converter and electrolyzer sets connected with concentrator photovoltaic (CPV) modules have been accomplished in the University of Miyazaki, Japan. The daily high efficiency of solar to hydrogen (~17% on sunny day and ~15% on cloudy day) was obtained from the system by using high efficiency CPV modules connected with multiple converter and electrochemical cells.
DOI： 10.24752/gre.1.0_44
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中赤外発光受光素子用III-V(Sb)系材料の結晶成長と評価 Reviewed
荒井 昌和，高橋 翔, 井上 裕貴, 藤原 由生, 吉元 圭太，山形 勇也，西岡 賢祐, 前田 幸治
レーザー研究 45 ( 12 ) 768 - 772 2017.12
Language：Japanese Publishing type：Research paper (scientific journal)
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A new solar to hydrogen conversion system with high efficiency and flexibility Reviewed
Yamashita D., Nakao H., Yonezawa Y., Nakashima Y., Ota Y., Nishioka K., Sugiyama M.
2017 6th International Conference on Renewable Energy Research and Applications, ICRERA 2017 441 - 446 2017.12
Language：English Publishing type：Research paper (international conference proceedings)
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Estimation of conversion efficiency for partially static concentrator with III-V on Si solar cell Reviewed
Ota Y., Araki K., Lee K., Yamaguchi M., Nishioka K.
AIP Conference Proceedings 1881 020010-1 - 020010-5 2017.9
Language：English Publishing type：Research paper (international conference proceedings)
DOI： 10.1063/1.5001409
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Quantifying the potential of III-V/Si partial concentrator by a statistical approach Reviewed
Lee K., Araki K., Ota Y., Nishioka K., Yamaguchi M.
AIP Conference Proceedings 1881 2017.9
Language：English Publishing type：Research paper (international conference proceedings) Publisher：AIP Conference Proceedings
© 2017 Author(s). We propose a theoretical framework for analyzing the energy yields of partial concentrators. A partial concentrator uses a concentrator cell to absorb the principal defracted or reflected light rays from its concentrator optics and a backplane cell to absorbs the diffused or defocused light. This concept can be applied to the concentrator system when accurate sun-tracking is not available, such as on a vehicle. This analysis framework provides a simplified way to describe the uncertainties of solar incidences dealt by partial concentrator. This help identified a clearer design criteria of partial concentrator in order to outperform the flat-panel PV or conventional CPV.
DOI： 10.1063/1.5001445
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Outdoor validation of the 30 minutes intermittent tracking of 100 x CPV Reviewed
Araki K., Ota Y., Lee K., Nishioka K., Yamaguchi M.
AIP Conference Proceedings 1881 2017.9
Language：English Publishing type：Research paper (international conference proceedings) Publisher：AIP Conference Proceedings
© 2017 Author(s). HCPV uses trackers, but their cost and reliability have raised problems. These problems may be solved by substantially increasing acceptance angle and mechanical tolerance. For a demonstration of the possibility of such substantial improvement, a 30 minutes intermittent tracking in high concentration applications was examined. To allow for 30 minutes intermittent tracking, both advanced optics and an advanced tracking control were investigated. For advanced optics, a 100 x refractive and dielectric concentrator was designed. It had about plus or minus 5°of acceptance angle. For advanced tracking control, a feed-forward control with a linear error correction was investigated. With combining both optimizations, it was shown that 30 minutes intermittent tracking was validated in outdoor experiments even for an as high as 100 x concentration.
DOI： 10.1063/1.5001401
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Optical and thermal simulation for wide acceptance angle CPV module Reviewed
Ahmad N., Ota Y., Araki K., Lee K., Yamaguchi M., Nishioka K.
AIP Conference Proceedings 1881 2017.9
Language：English Publishing type：Research paper (international conference proceedings) Publisher：AIP Conference Proceedings
© 2017 Author(s). Concentrator photovoltaic (CPV) technology has the potential to decrease the cost of systems in the near future by using less expensive optical elements in the system which replace the receiving surface aperture and concentrate the sunlight onto small solar cells. One of the main concerns of CPV is the need for high precision tracking system and the relation to the acceptance angle. In this paper, we proposed a CPV module with concentration ratio larger than 100 times and wide acceptance angle. An optical simulation for the module with S-TIM2 glass as a lens material was conducted to estimate the optical performance of the module. Thermal and electrical simulation was also conducted using COMSOL Multiphysics and SPICE respectively to evaluate the working temperature and electrical characteristics of the multijunction solar cell under concentration conditions.
DOI： 10.1063/1.5001400
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Is it CPV? Yes, but it is a partial CPV Reviewed
Araki K., Ota Y., Lee K., Nishioka K., Yamaguchi M.
AIP Conference Proceedings 1881 2017.9
Language：English Publishing type：Research paper (international conference proceedings) Publisher：AIP Conference Proceedings
© 2017 Author(s). III-V on Si cell is one of the most promising candidates of the low-cost and high-efficiency solar cell beyond the limit of Si cells. However, it is likely that the cost of III-V cell will keep greater than that of Si cells. The partial concentrator technology was invented to concentrate the sunlight onto smaller III-V cells on the Si cell with the increased acceptance angle for static concentrator operation. The partial concentrator allows on-axis optical loss but expands the apparent acceptance angle often beyond the thermodynamic limit. The spilled light will be saved and collected by the bottom Si cell. It is not just placing the Si cell around the concentrated III-V cell, but its design philosophy is "partially" collecting the sunlight to the III-V cell to expand the acceptance. Depending on the values of cost parameters, the cost of the partial CPV module becomes minimum at 4 x - 10 x of concentration onto the top III-V cell, meaning that the area of expensive III-V cell can be saved to 1/4 - 1/10. In the partial concentrator. There may be a better optics than the ideal concentrator. The partial concentrator can be applied not only to III-V on Si cells but also III-V "by" Si cells. This lateral configuration does not have as excellent efficiency as the III-V on Si cell, but the usage of III-V cell is only several percents of the Si cell and has good similarity on the conventional Si flat-plate module technology.
DOI： 10.1063/1.5001439
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Design of the partial concentrator lens for III-V on Si static concentration Reviewed
Araki K., Ota Y., Lee K., Nishioka K., Yamaguchi M.
AIP Conference Proceedings 1881 2017.9
Language：English Publishing type：Research paper (international conference proceedings) Publisher：AIP Conference Proceedings
© 2017 Author(s). To compete with the flat-plate crystalline Silicon cell module, III-V on Si structure is developed. However, it is clear that the situation of the higher cost of III-V cell relative to the Silicon cell will be unchanged. Then, it is preferred concentrating III-V cell for further savings. The partial concentrator is expanding the acceptance angle despite the higher concentration ratio. It is achieved by better performance balance of on-axis and high incidence angle. The new and generalized design method of the partial concentrator was developed. The profile function was constructed by selected Zernike's polynomial considering rotational symmetry. The full conditions of the calculation including the initial value and the radial and azimuthal degree of the function were examined. It was found that the recommended radial and azimuthal degree were 12 and 12.
DOI： 10.1063/1.5001412
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Ahmad N., Ota Y., Araki K., Lee K., Yamaguchi M., Nishioka K.
Japanese Journal of Applied Physics 56 ( 9 ) 092301-1 - 092301-8 2017.8
Language：English Publishing type：Research paper (scientific journal) Publisher：Institute of Physics
In this study, we propose a new concentrator photovoltaic (CPV) system design with a large-acceptance-angle lens, which tracks the sun on the basis of a new 30-min intermittent tracking method that does not require a special high-precision CPV tracking system. This will reduce costs, because a large percentage of the cost of a typical CPV system comes from the expensive accurate tracking system. The present system had a concentration ratio of 111 and an acceptance angle of 4.5°. We conducted an experiment to evaluate the thermal and electrical performances of the system in an outdoor test site in Miyazaki, Japan. The experimental results were compared with optical, thermal, and electrical simulation results. The simulated results showed good agreement with the experimental ones.
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Yoshino K., Tominaga H., Ide A., Nishioka K., Naka T.
Physica Status Solidi (C) Current Topics in Solid State Physics 14 ( 6 ) 16001777 2017.6
Language：English Publishing type：Research paper (scientific journal) Publisher：Physica Status Solidi (C) Current Topics in Solid State Physics
© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Polycrystalline a-axis oriented Ga-doped ZnO thin film could be grown on glass substrate by a conventional atmospheric spray pyrolysis at 150 °C using diethylzinc-based solution. The n-type Ga-doped ZnO thin film had a resistivity of 1.5 × 10 −3 Ω cm, a carrier concentration of 2.0 × 10 20 cm −3 and a mobility of 20.0 cm 2 (Vs) −1 at an optimal Ga content of 2 wt.% upon hydrogen annealing at 450 °C. It was assumed that an increase of the n-type carrier concentration is due to increase oxygen vacancies by reacting hydrogen and oxygen in ZnO from X-ray photoelectron spectroscopy.
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Ikari T., Ohori D., Higo A., Thomas C., Samukawa S., Nishioka K., Fukuyama A.
Nanotechnology Materials and Devices Conference, NMDC 2016 - Conference Proceedings 2016.12
Language：English Publishing type：Research paper (international conference proceedings) Publisher：Nanotechnology Materials and Devices Conference, NMDC 2016 - Conference Proceedings
© 2016 IEEE. This New top-down fabrication process using bio-template and neutral beam etching process have succeeded to grow GaAs quantum nano disc (ND) for optical communication devices. The size, the alignment and the density of ND were well controlled. Low temperature photoluminescence measurement confirmed that the quantum energy levels were formed in the present structure and made clear the usefulness of the top-down process toward a defect-free ND fabrication. Strong luminescence was observed even in an as-etched samples.
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Optimization of static concentrator photovoltaics with aspherical lens for automobile
Ota Y., Nishioka K., Araki K., Ikeda K., Lee K., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 2016-November 570 - 573 2016.11
Language：English Publishing type：Research paper (international conference proceedings) Publisher：Conference Record of the IEEE Photovoltaic Specialists Conference
© 2016 IEEE. In this paper, we optimized the basic aspherical lens for automobile using optical method. Since the panel is installed in horizontal, the distribution of incident angle that is important to concentrator optics design needs to be newly defined. By optimization of lens structure, the optical efficiency increased to 46.7%.
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Possibility of CPV for automobile energy source
Araki K., Ota Y., Ikeda K., Lee K., Nishioka K., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 2016-November 554 - 559 2016.11
Language：English Publishing type：Research paper (international conference proceedings) Publisher：Conference Record of the IEEE Photovoltaic Specialists Conference
© 2016 IEEE. Greenhouse gas emission from automobiles cannot be eliminated before having them run by the sun. Toyota Tec. Inst. is serious to develop CPV applications to automobile. One is an innovative static concentrator that selectively collects sunlight from shallow angle. Another is a solar powered EV charging station with practical size and capacity.
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Ota Y., Ahmad N., Nishioka K.
Solar Energy 136 547 - 552 2016.10
Language：English Publishing type：Research paper (scientific journal) Publisher：Solar Energy
© 2016 Elsevier Ltd The amount of radiation received by the solar cells inside a photovoltaic (PV) module is lower than that arriving at the module surface, owing to reflection and soiling of the module surface. To develop high-efficiency PV systems, these effects must be addressed. In this study, a silica-based layer with anti-reflection and anti-soiling properties was coated onto the surface of a Cu(In, Ga)Se 2 PV module and the effects were assessed. The coating method was simple, allowing it to be applied to already installed PV modules. The cleaning and coating treatments were carried out on December 25, 2014, and the arrays were exposed outdoors for 7 months to investigate the effects of the treatment. The output of the array that received the coating was 3.2% greater than that of an uncoated array. It was also found that the coating reduced the reflection of the light entering from a high incident angle.
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Possibility of static low concentrator PV optimized for vehicle installation Reviewed
Araki K., Ota Y., Ikeda K., Lee K., Nishioka K., Yamaguchi M.
AIP Conference Proceedings 1766 2016.9
Language：English Publishing type：Research paper (international conference proceedings) Publisher：AIP Conference Proceedings
© 2016, American Institute of Physics Inc. All rights reserved. One of the most direct and efficient ways in eliminating greenhouse gas emission from cars is to install a PV panel on the roof. Since the area of the roof of the car is limited, high-efficiency III-V cells will be useful. Because of the space limitation, it should be high-efficiency panel. III-V cells may be a candidate, but it should be CPV for saving cost of the cell. Considering its quick movement and appearance, trackers were thought difficult to implement. Our choice was a static concentrator customized to automobile. Special static concentrator that collects sunlight from shallow incident angle was successfully developed.
DOI： 10.1063/1.4962069
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Intermittent tracking (30 minutes interval) using a wide acceptance CPV module Reviewed
Araki K., Ota Y., Lee K., Nishioka K., Yamaguchi M.
AIP Conference Proceedings 1766 2016.9
Language：English Publishing type：Research paper (international conference proceedings) Publisher：AIP Conference Proceedings
© 2016, American Institute of Physics Inc. All rights reserved. For applications of stand-alone systems including an electric vehicle (EV) power station, a tracking system with low power consumption will be demanded. One possible solution to save idling power is intermittent tracking, for example, tracking in every 30 minutes. To achieve this, a new CPV module was designed. With the combination of an advanced feed-forward tracking control, the 30 minutes of intermittent tracking may be possible by 100 x of geometrical concentration (the projected lens area by the cell aperture area with alignment margin).
DOI： 10.1063/1.4962083
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Damage repair of lens surface in CPV by silica based coating Reviewed
Kurogi S., Ota Y., Yoshino K., Nishioka K.
AIP Conference Proceedings 1766 2016.9
Language：English Publishing type：Research paper (international conference proceedings) Publisher：AIP Conference Proceedings
© 2016, American Institute of Physics Inc. All rights reserved. We tried to repair the surface of damaged poly-methyl methacrylate and glass using a simple coating and evaluated the transmittance of direct component of light. We coated a repairing material on the damaged surface of the sample. After the first sandblasting, the transmittance and the calculated conversion efficiency of CPV decreased due to the damage derived by the sandblasting. However, after the first coating, they made a recovery due to the effect of the repairing coating. In the second step (sandblasting and coating), the recovery was also observed. Instead of replacement of damaged lens or module, the coating can bring the performance back into the improved condition.
DOI： 10.1063/1.4962079
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Carbothermal reduction process of silica formed from shirasu volcanic ash using solar furnace Reviewed
Hatakeyama K., Sato K., Nishioka K.
MATEC Web of Conferences 65 2016.7
Language：English Publishing type：Research paper (international conference proceedings) Publisher：MATEC Web of Conferences
© 2016 Owned by the authors, published by EDP Sciences. Metallurgical grade silicon was formed using Shirasu volcanic ash as starting material with solar furnace. The solar furnace was composed of two parts: Fresnel lens and reacting furnace. The reacting furnace was composed of a cylindrical vacuum chamber and quartz glass plate functioning to guide the concentrated sunlight into the furnace, and was placed at the focal point of the Fresnel lens. The sample was made from a mixture of silica formed from Shirasu volcanic ash and carbon, and placed in the carbon crucible inside the reacting furnace. The sample was irradiated for 3 hours, and the furnace was left until it cooled down to room temperature. After the cooling process, the sample was mixed and placed in the carbon crucible, and it was irradiated and cooled with the same processes again. After the experiment, the sample was evaluated by X-ray diffraction and the production of silicon was confirmed.
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Ahmad N., Hatakeyama K., Ota Y., Nishioka K.
MATEC Web of Conferences 65 2016.7
Language：English Publishing type：Research paper (international conference proceedings) Publisher：MATEC Web of Conferences
© 2016 Owned by the authors, published by EDP Sciences. This paper presents a comparison of three-dimensional simulation for concentrator photovoltaic module using two types of multi-junction solar cell. Each had its own range of spectral response and based on that range a thin film filter was developed for each case to reflect the unused spectral of the solar spectrum and allowed the desired spectrum to reach the solar cell. The thin film was deposited on a secondary optical element that was used to homogenize the irradiance distribution on the solar cell. A thermal simulation was conducted to compare the resulted decrease in cell temperature due to the use of the thin film for each case.
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Reduction of temperature in silicon photovoltaic module using thermal radiation coating Reviewed
Nakamura S., Nishioka K.
MATEC Web of Conferences 65 2016.7
Language：English Publishing type：Research paper (international conference proceedings) Publisher：MATEC Web of Conferences
© 2016 Owned by the authors, published by EDP Sciences. The temperature of solar cells increases under the actual operating conditions, and the conversion efficiency of solar cells decreases with increasing temperature. In this study, a thermal radiation layer was coated on the back sheet of the PV module by a spray coating method and the effect was evaluated. The thickness of the layer was 30 μm. The temperature of the PV module with the thermal radiation coating was lower than that of the PV module without the thermal radiation coating. And the operating temperature range of the PV module with the thermal radiation coating was decreased by 2~3°C. The open-circuit voltage of the PV module with the thermal radiation coating was 0.1 V higher than that of the module without the coating due to the thermal radiation coating.
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Nakamura S., Sakamoto K., Nishioka K.
MATEC Web of Conferences 65 2016.7
Language：English Publishing type：Research paper (international conference proceedings) Publisher：MATEC Web of Conferences
© 2016 Owned by the authors, published by EDP Sciences. The temperature of solar cells considerably increases under light-concentrating operations, and the conversion efficiency of solar cells decreases with increasing temperature. It is very important to reduce the cell temperature in concentrator photovoltaic modules. The thermal radiation layers with high thermal emissivity and thermal conductivity was coated on the aluminum samples which is used for the chassis of concentrator photovoltaic and the effect was evaluated under the conditions with wind. The temperature of sample with coating showed lower temperature than that without coating. In the condition with wind, the coated sample with high thermal emissivity and high thermal conductivity showed the lowest temperature due to the effect of thermal radiation and thermal conduction.
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Outdoor Performance Comparison of Concentrator Photovoltaic and Flat Plate Photovoltaic Systems Reviewed
Hidaka Y., Imai K., Ota Y., Nishioka K.
MATEC Web of Conferences 65 2016.7
Language：English Publishing type：Research paper (international conference proceedings) Publisher：MATEC Web of Conferences
© 2016 Owned by the authors, published by EDP Sciences. Output characteristics of tracking type concentrator photovoltaic (CPV) system, multi-crystalline silicon (mc-Si) PV system, CIGS PV system, and amorphous silicon (a-Si) PV system were analyzed in the data period of a year from August 2013 to July 2014. In this study, we analyzed the influence of environmental factors using average photon energy (APE) and temperature of solar cell (T cell ). The characteristics of 14 kW CPV system, 50 kW mc-Si PV system, 60 kW CIGS PV system, 1.35 kW a-Si PV system were evaluated and compared. As a result, the output performance of CPV was highest between the four systems at the most frequent conditions in the outdoor environment.
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Sugiyama M., Nakamura A., Watanabe K., Ota Y., Nishioka K., Nakano Y., Fujii K.
2015 IEEE 42nd Photovoltaic Specialist Conference, PVSC 2015 2015.12
Language：English Publishing type：Research paper (international conference proceedings) Publisher：2015 IEEE 42nd Photovoltaic Specialist Conference, PVSC 2015
© 2015 IEEE. Solar hydrogen production is one of the most re-quired technologies for the realization of sustainable energy sys-tems which is independent of fossil fuel. The solar-to-hydrogen (STH) energy conversion efficiency for photocatalysts, which have been studied quite intensively for decades, remains much lower than 10%. The combination of photovoltaic and electrochemical cells, on the other hand, can easily achieve the STH efficiency over 10%. We here present the field demonstration of a system combin-ing a concentrator photovoltaic (CPV) module and polymer elec-trolyzers, which led us to the STH efficiency of 17.1%. A method will be presented to optimize the series/parallel connection be-tween CPV and electrolyzers for maximizing the STH, which pre-dicts 28% STH when 35%-efficient CPV module is used.
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0619 The Effect of the Slit width having the CPV of Three-divided-Panel Type Reviewed
OGAWA Kazuma, OZONO Shigehira, NISHIOKA Kensuke
Fluids engineering conference ... 2015 "0619 - 1"-"0619-3" 2015.11
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers
This paper deals with the aerodynamic characteristics of the concentrated photovoltaic system (i.e. CPV) of three-divided-panel type. A preceding experimental study indicates that the moment around the shaft supporting the panel decreases when the acceptance surface of the panel faces downstream ('downstream case'). To investigate the mechanism, we conducted measurements on the aerodynamic forces in a wind tunnel. It is found that as the slit width increases, the moment gradually decreases to small values when the acceptance surface faces downstream. This reduction probably comes from uniformity of the pressure distribution on the rear surface for the downstream case.
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A 24.4% solar to hydrogen energy conversion efficiency by combining concentrator photovoltaic modules and electrochemical cells Reviewed
Akihiro Nakamura, Yasuyuki Ota, Kayo Koike, Yoshihide Hidaka, Kensuke Nishioka, Masakazu Sugiyama, Katsushi Fujii
Applied Physics Express 8 ( 10 ) 107101-1 - 107101-4 2015.10
Language：English Publishing type：Research paper (scientific journal)
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Field test analysis of concentrator photovoltaic system focusing on average photon energy and temperature Reviewed
Husyira Al Husna, Yasuyuki Ota, Takashi Minemoto, Kensuke Nishioka
Japanese Journal of Applied Physics 54 ( 8S1 ) 08KE05-1 - 08KE05-4 2015.8
Language：English Publishing type：Research paper (scientific journal)
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Anti-soiling coating based on silica for Fresnel lens of concentrator photovoltaics Reviewed
Takuya Hirohata, Yasuyuki Ota, Kensuke Nishioka
Japanese Journal of Applied Physics 54 ( 8S1 ) 08KE09-1 - 08KE09-4 2015.8
Language：English Publishing type：Research paper (scientific journal)
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Effect of aerosols on performance of concentrator photovoltaics Reviewed
Kei Nomura, Kenta Imai, Yasuyuki Ota, Takashi Minemoto, Kensuke Nishioka
Japanese Journal of Applied Physics 54 ( 8S1 ) 08KE07-1 - 08KE07-4 2015.8
Language：English Publishing type：Research paper (scientific journal)
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降灰が太陽光発電システム出力におよぼす影響 Reviewed
西岡 賢祐, 太田 靖之
電気設備学会誌 35 ( 5 ) 348 - 353 2015.5
Language：Japanese Publishing type：Research paper (scientific journal)
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2分割型太陽光発電システムの空力特性 Reviewed
小川 和馬, 柳ヶ瀬 光, 小園 茂平, 西岡 賢祐
第23回風工学シンポジウム論文集 289 - 294 2015.3
Language：Japanese Publishing type：Research paper (scientific journal)
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Formation of Silicon Carbide Using Volcanic Ash as Starting Material and Concentrated Sunlight as Energy Resource Reviewed
Kensuke Nishioka, Junki Komori, Kouji Maeda, Yasuyuki Ota, Hiroshi Kaneko, Kosei Sato
International Journal of Photoenergy 2015 ID394605 1 - ID394605 4 2015.3
Language：English Publishing type：Research paper (scientific journal)
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Uniqueness verification of direct solar spectral index for estimating outdoor performance of concentrator photovoltaic systems Reviewed
Jakapan Chantana, Seiya Ueno, Yasuyuki Ota, Kensuke Nishioka, Takashi Minemoto
Renewable Energy 75 762 - 766 2015.3
Language：English Publishing type：Research paper (scientific journal)
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集光太陽光の活用技術 Invited Reviewed
西岡賢祐
安全工学 53 ( 6 ) 425 - 430 2014.12
Language：Japanese Publishing type：Research paper (scientific journal)
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Estimation of operating temperature and energy output of concentrator photovoltaic module under concentration conditions Reviewed
Yasuyuki Ota, Kensuke Nishioka
Japanese Journal of Applied Physics 53 ( 12 ) 122301-1 - 122301-5 2014.12
Language：English Publishing type：Research paper (scientific journal)
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Seasonal variation of performance in concentrator photovoltaic system Reviewed
Kei Nomura, Yasuyuki Ota, Takashi Minemoto, Kensuke Nishioka
physica status solidi (c) 11 ( 7 ) 1427 - 1430 2014.9
Language：English Publishing type：Research paper (scientific journal)
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Effect of Alcohol-Assisted Annealing on the Quality of Silicon Oxide Thin Film Reviewed
Takuya Ito, Yasuyuki Ota, Koichiro Shiomori, Kensuke Nishioka
Journal of Electronic Materials 43 ( 7 ) 2683 - 2687 2014.7
Language：English Publishing type：Research paper (scientific journal)
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Output Estimation of Concentrator Photovoltaic Using Mappings of Environmental Factors and Performance Ratio Reviewed
K. Nomura, Y. Ota, T. Minemoto and K. Nishioka
ACTA PHYSICA POLONICA A 125 ( 4 ) 1021 - 1023 2014.4
Language：English Publishing type：Research paper (scientific journal)
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Estimation of thermal stress in concentrator cells using structural mechanics simulation Reviewed
Yasuyuki Ota, Kensuke Nishioka
AIP Conference Proceedings (10TH INTERNATIONAL CONFERENCE ON CONCENTRATING PHOTOVOLTAIC SYSTEMS: CPV-10) 1616 25 - 28 2014.4
Language：English Publishing type：Research paper (scientific journal)
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Proposition of a New Valid Utilization for Shirasu Volcanic Ash Using Renewable Energy Reviewed
Kosei Sato, Kouji Maeda and Kensuke Nishioka
Advanced Materials Research 894 149 - 153 2014.2
Language：English Publishing type：Research paper (scientific journal)
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Temperature Characteristics of Concentrator Photovoltaics Analyzed by Circuit Calculation Reviewed
Kensuke Nishioka, Kosei Sato and Yasuyuki Ota
Advanced Materials Research 894 234 - 237 2014.2
Language：English Publishing type：Research paper (scientific journal)
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Impact of Sandblasting on Fresnel Lens for Concentrator Photovoltaic Reviewed
Kensuke Nishioka, Kosei Sato and Yasuyuki Ota
Advanced Materials Research 894 250 - 253 2014.2
Language：English Publishing type：Research paper (scientific journal)
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Low Temperature Formation of Silicon Oxide Thin Film and Modification of Film Quality by Argon Excimer Light Reviewed
Kensuke Nishioka, Kosei Sato, Takuya Ito and Yasuyuki Ota
Advanced Materials Research 894 408 - 411 2014.2
Language：English Publishing type：Research paper (scientific journal)
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Control of the texture structure size in anisotropic etching of silicon Reviewed
Junki Komori, Tsuyoshi Sueto and Kensuke Nishioka
Advanced Materials Research 893 174 - 177 2014.2
Language：English Publishing type：Research paper (scientific journal)
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Hydrophilic silica thin film formed using dimethyl silicone oil and ozone Reviewed
Hiroyuki Arima, Takuya Ito, and Kensuke Nishioka
Advanced Materials Research 893 524 - 527 2014.2
Language：English Publishing type：Research paper (scientific journal)
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Evaluation of performance in bifacial solar cell Reviewed
Takuo Notohara, Koichi Sugibuchi, Shinji Goda, Naoki Ishikawa, Yasuyuki Ota and Kensuke Nishioka
Advanced Materials Research 893 755 - 759 2014.2
Language：English Publishing type：Research paper (scientific journal)
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Output characteristic analysis of partially shaded back surface of bifacial photovoltaic solar module Reviewed
Naoki Sawano, Takuo Notohara, Yasuyuki Ota, and Kensuke Nishioka
Advanced Materials Research 893 769 - 772 2014.2
Language：English Publishing type：Research paper (scientific journal)
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Impact of Spectral Irradiance Distribution and Temperature on Concentrator Photovoltaic System Reviewed
Kensuke Nishioka and Yasuyuki Ota
Advanced Materials Research 893 773 - 776 2014.2
Language：English Publishing type：Research paper (scientific journal)
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Pattern Formation of Silicon Oxide Thin Film with Ink Mask Reviewed
Takuya Ito, Yasuyuki Ota, Kensuke Nishioka
Applied Mechanics and Materials 481 98 - 101 2014.1
Language：English Publishing type：Research paper (scientific journal)
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521 Measurement of Instantaneous Heat Flux on Light Condensing Spot of Beam-Down Solar Concentrator Reviewed
NAGASE Yoshinori, HARAKAWA Tsuyoshi, KAWAMURA Ryuusuke, TOMOMATSU Shigeki, KANEKO Hiroshi, NISHIOKA Kensuke, KODAMA Tatsuya, GOKON Nobuyuki, MATSUBARA Koji
2014 ( 67 ) "521 - 1"-"521-2" 2014
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers
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Suppression of dust adhesion on a concentrator photovoltaic module using an anti-soiling photocatalytic coating Reviewed
Tsuyoshi Sueto, Yasuyuki Ota, Kensuke Nishioka
Solar Energy 97 414 - 417 2013.11
Language：English Publishing type：Research paper (scientific journal)
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散乱比と傾斜面全天日射量を用いた集光型太陽光発電システムの導入指標 Reviewed
末藤 豪, 太田 靖之, 荒木 建二, 熊谷 伊三夫, 西岡 賢祐
電気設備学会誌 33 ( 7 ) 547(111) - 552(116) 2013.7
Language：Japanese Publishing type：Research paper (scientific journal)
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Effect of anti-soiling coating on performance of Fresnel lens for concentrator photovoltaic module Reviewed
Takuya Hirohata, Yasuyuki Ota, Kensuke Nishioka
Applied Mechanics and Materials 372 575 - 578 2013.7
Language：English Publishing type：Research paper (scientific journal)
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Heat release effect of thermal emission coating on concentrator photovoltaic module Reviewed
Kensuke Nishioka, Yasuyuki Ota
Applied Mechanics and Materials 372 559 - 562 2013.7
Language：English Publishing type：Research paper (scientific journal)
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Photovoltaic Systems in University of Miyazaki Reviewed
Kenji Yoshino, Kensuke Nishioka, Atsuhiko Fukuyama, Hidetoshii Suzuki, Masahisa Otsubo
Applied Mechanics and Materials 372 555 - 558 2013.7
Language：English Publishing type：Research paper (scientific journal)
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Saito N., Fujita M., Nakaaki I., Yamawaki S., Iwata H., Nishioka K.
Journal of Non-Crystalline Solids 376 81 - 85 2013.6
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Journal of Non-Crystalline Solids
Hydrogenated silicon-carbon alloy (SiC:H) films were deposited by reactive RF magnetron sputtering of Si in methane-argon gas mixtures. As a second sputtering gas, helium was used to control the film properties. The effect of the partial pressure ratio (R) of He to the total sputtering gas on the structural, optical, and electrical properties of the films was investigated. At R values above 70%, the bonding configuration observed in the IR spectra changed, the optical band gap decreased, and the DC conductivity clearly increased. These observations imply an increase in structural disorder after introducing a high R of He during the sputtering process. In order to overcome the negative effects on the properties of films deposited under high R values, the possibility of micro-crystallization in an amorphous structure was examined by introducing H 2 instead of He. © 2013 Elsevier B.V.
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Superhydrophobic Silicon Surface with Micro/Nano-Composite Structure Formed by 2-Step Wet Etching Reviewed
Kensuke Nishioka and Takatoshi Yasui
Advanced Materials Research 747 542 - 546 2013.6
Language：English Publishing type：Research paper (scientific journal)
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Effect of Photocatalytic Coating on Concentrator Photovoltaic Module Reviewed
Tsuyoshi Sueto and Kensuke Nishioka
Advanced Materials Research 747 337 - 340 2013.6
Language：English Publishing type：Research paper (scientific journal)
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Effect of Heat Treatment on High Purity Nanoporous Silica Formed from Volcanic Ash Deposit Shirasu Reviewed
Kosei Sato, Toshinori Kokubu, and Kensuke Nishioka
Advanced Materials Research 747 547 - 550 2013.6
Language：English Publishing type：Research paper (scientific journal)
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Thermal Transfer Simulation For Concentrator Photovoltaic Receiver Under Concentration Condition Reviewed
Yasuyuki Ota, Hirokazu Nagai, Kenji Araki, Kensuke Nishioka
AIP Conference Proceedings (9TH INTERNATIONAL CONFERENCE ON CONCENTRATING PHOTOVOLTAIC SYSTEMS: CPV-9) 1556 18 - 21 2013.4
Language：English Publishing type：Research paper (international conference proceedings)
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Impact of spectral irradiance distribution and temperature on the outdoor performance of concentrator photovoltaic system Reviewed
Husyira Al Husna, Naoki Shibata, Naoki Sawano, Seiya Ueno, Yasuyuki Ota, Takashi Minemoto, Kenji Araki, Kensuke Nishioka
AIP Conference Proceedings (9TH INTERNATIONAL CONFERENCE ON CONCENTRATING PHOTOVOLTAIC SYSTEMS: CPV-9) 1556 252 - 255 2013.4
Language：English Publishing type：Research paper (international conference proceedings)
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Reduction of Operating Temperature in 25 Series-Connected 820X CPV Reviewed
Yasuyuki Ota, Tsuyoshi Sueto, Hirokazu Nagai, Kenji Araki, Kensuke Nishioka
Japanese Journal of Applied Physics 52 04CR03-1 - 04CR03-4 2013.3
Language：English Publishing type：Research paper (scientific journal)
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Control of Pore Size of High Purity Nanoporous Silica Formed from Volcanic Ash Deposit Shirasu Reviewed
Kosei Sato, Toshinori Kokubu, Kensuke Nishioka
Advanced Materials Research 622-633 970 - 974 2013.2
Language：English Publishing type：Research paper (scientific journal)
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Heat reduction of concentrator photovoltaic module using high radiation coating Reviewed
Kensuke Nishioka, Yasuyuki Ota, Kazuyuki Tamura, Kenji Araki
Surface and Coatings Technology 215 472 - 475 2013.1
Language：English Publishing type：Research paper (scientific journal)
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Improvement of Electrical Properties of Silicon Oxide Thin Film with Ultraviolet and Organic Gas Assisted Annealings Reviewed
Takuya Ito, Takuya Matumoto, Kensuke Nishioka
Surface and Coatings Technology 215 447 - 451 2013.1
Language：English Publishing type：Research paper (scientific journal)
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Effect of Anti-Soiling Layer Coated on Poly(methyl methacrylate) for Concentrator Photovoltaic Modules Reviewed
Kenji Nabemoto, Yuya Sakurada, Yasuyuki Ota, Kazuyuki Takami, Hirokazu Nagai, Kazuyuki Tamura, Kenji Araki, Kensuke Nishioka
Japanese Journal of Applied Physics 51 ( 10 ) 10ND11.1 - 10ND11.3 2012.10
Language：English Publishing type：Research paper (scientific journal)
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Sandblasting durability of acrylic and glass Fresnel lenses for concentrator photovoltaic modules Reviewed
Kensuke Nishioka, Kenichi Ikematsu, Yasuyuki Ota, Kenji Araki
Solar Energy 86 ( 10 ) 3021 - 3025 2012.10
Language：English Publishing type：Research paper (scientific journal)
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Evaluation of Organic Thin Film Solar Cells Using 3-Diode Equivalent Circuit Model with Inverted Diode Reviewed
Yuya Sakurada, Yasuyuki Ota, Hiroki Watanabe, Hideyuki Murata, Kensuke Nishioka
Materials Science Forum 725 179 - 182 2012.8
Language：English Publishing type：Research paper (scientific journal)
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2-Dimensional Mapping of Power Consumption Due to Electrode Resistance Using Simulator for Concentrator Photovoltaic Module Reviewed
Yasuyuki Ota, Yuya Sakurada, Kensuke Nishioka
Materials Science Forum 725 183 - 186 2012.8
Language：English Publishing type：Research paper (scientific journal)
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Two-Dimensional Mapping of Power Consumption Due to Series Resistance Evaluated by Simulator for Concentrator Photovoltaic Module Reviewed
Yasuyuki Ota and Kensuke Nishioka
Japanese Journal of Applied Physics 51 ( 2-2-02BP03 ) 1 - 4 2012.2
Language：English Publishing type：Research paper (scientific journal)
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Structural and electrical properties of Ni-Cr oxide films prepared by magnetron sputtering Reviewed
N. Saito, I. Nakaaki, H. Iwata, K. Nishioka
Thin Solid Films 520 3031 - 3034 2012.1
Language：English Publishing type：Research paper (scientific journal)
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Sakurada Y., Ota Y., Nishioka K.
AIP Conference Proceedings 1407 216 - 219 2011.12
Language：English Publishing type：Research paper (international conference proceedings) Publisher：AIP Conference Proceedings
Using spice diode model, the temperature characteristics of an InGaP/InGaAs/Ge triple-junction solar cell under concentrated light conditions were analyzed in detail. The current-voltage (I-V) characteristics of the single-junction solar cells (InGaP, InGaAs, and Ge solar cells) were measured at various temperatures. From dark I-V characteristics of each single-junction solar cell, the diode parameters and temperature exponents were extracted. The extracted diode parameters and temperature exponents were applied to the equivalent circuit model for the triple-junction solar cell, and the solar cell performance was calculated with considering the temperature characteristics of series resistance. There was good agreement between the measured and calculated I-V characteristics of the triple-junction solar cell at various temperatures under concentrated light conditions. © 2011 American Institute of Physics.
DOI： 10.1063/1.3658330
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Investigation of the photovoltaic performance of the polycrystalline silicon p–n junction by a photothermal measurement Reviewed
Atsuhiko Fukuyama, Daisuke Ishibashi, Yohei Sato, Kentaro Sakai, Hidetoshi Suzuki, Kensuke Nishioka, Tetsuo Ikari
Journal of Non-Crystalline Solids 2011.12
Language：English Publishing type：Research paper (scientific journal)
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Anti-soiling layer coarted on PMMA Fresnel lens for concentrator photovoltaic modules
Nishioka K., Nabemoto K., Sakurada Y., Ota Y., Takami K., Nagai H., Araki K.
Conference Record of the IEEE Photovoltaic Specialists Conference 003332 - 003334 2011.12
Language：English Publishing type：Research paper (international conference proceedings) Publisher：Conference Record of the IEEE Photovoltaic Specialists Conference
An anti-soiling layer was coated on the PMMA substrates. The anti-soiling layer was prepared by coating the inorganic/organic nano-graded intermediate layer (Ube-Nitto Kasei Co., Ltd.) and photocatalytic surface layer including modified WO 3 (ILUMIO®, Sumitomo Chemical Co., Ltd.) and partial hydrolyzed tetraethylorthosilicate (Wako Pure Chemical Industries, Ltd.). After 6 months, the reduction rate of photocurrent without anti-soiling coat was 7.5%. On the other hand, that with anti-soiling coat could be suppressed to 3%. The experimental environment of the exposure site is clean, and there is a lot of rainfall. It is considered that the effect of the anti-soiling coat must be more significant if CPV systems are installed in dusty areas. © 2011 IEEE.
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Three-dimensional simulating of concentrator photovoltaic modules using ray trace and equivalent circuit simulators Reviewed
Yasuyuki Ota, and Kensuke Nishioka
Solar Energy 86 476 - 481 2011.11
Language：English Publishing type：Research paper (scientific journal)
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Water-Repellent Silicon Surface with Nanostructure Formed by Catalysis of Single Nanosized Silver Particle Reviewed
Kensuke Nishioka, Tsuyoshi Sueto, Kenji Yoshino, and Nobuo Saito
Japanese Journal of Applied Physics 50 ( 128003 ) 1 - 2 2011.11
Language：English Publishing type：Research paper (scientific journal)
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Simulation of Temperature Characteristics of InGaP/InGaAs/Ge Triple-Junction Solar Cell under Concentrated Light Reviewed
Yuya Sakurada, Yasuyuki Ota, and Kensuke Nishioka
Japanese Journal of Applied Physics 50 ( 4 ) 4 - 13 2011.4
Language：English Publishing type：Research paper (scientific journal)
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Temperature Characteristics Analysis of Triple‐Junction Solar Cell under Concentrated Conditions using Spice Diode Model Reviewed
Yuya Sakurada, Yasuyuki Ota, and Kensuke Nishioka
AIP Conference Proceedings (7TH INTERNATIONAL CONFERENCE ON CONCENTRATING PHOTOVOLTAIC SYSTEMS: CPV-7) 50 ( 4 ) 1 - 4 2011.4
Language：Japanese Publishing type：Research paper (international conference proceedings)
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Tracking Error analysis of Concentrator Photovoltaic Module Using Total 3‐Dimensional Simulator Reviewed
Yasuyuki Ota and Kensuke Nishioka
AIP Conference Proceedings (7TH INTERNATIONAL CONFERENCE ON CONCENTRATING PHOTOVOLTAIC SYSTEMS: CPV-7) 1407 281 - 284 2011.4
Language：English Publishing type：Research paper (international conference proceedings)
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Output comparison of CPV and flat-plate systems in Japanese meteorological condition Reviewed
Naoki Shibata, Yasuyuki Ota, Yuya Sakurada, Yasuhiro Takahashi, Isao Kumagai, Kenji Araki, and Kensuke Nishioka
AIP Conference Proceedings (7TH INTERNATIONAL CONFERENCE ON CONCENTRATING PHOTOVOLTAIC SYSTEMS: CPV-7) 1407 216 - 219 2011.4
Language：English Publishing type：Research paper (international conference proceedings)
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Detailed Analysis of Temperature Characteristics of an InGaP/InGaAs/Ge Triple-Junction Solar Cell Reviewed
Kensuke Nishioka, Tsuyoshi Sueto, Masaki Uchida, Yasuyuki Ota
Journal of Electronic Materials 39 ( 6 ) 704 - 708 2010.6
Language：English Publishing type：Research paper (scientific journal)
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Formation of antireflection nanostructure for silicon solar cells using catalysis of single nano-sized silver particle Reviewed
K. Nishioka, T. Sueto, N. Saito
Applied Surface Science 255 ( 23 ) 9504 - 9507 2009.9
Language：English Publishing type：Research paper (scientific journal)
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Enhancement of the crystalline quality of reactively sputtered yttria-stabilized zirconia by oxidation of the metallic target surface Reviewed
S. Hana, K. Nishioka, S. Horita
Thin Solid Films 517 ( 20 ) 5830 - 5836 2009.8
Language：English Publishing type：Research paper (scientific journal)
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Low-temperature deposition of silicon oxide film from the reaction of silicone oil vapor and ozone gas Reviewed
S. Horita, K. Toriyabe, K. Nishioka
Japanese Journal of Applied Physics 48 ( 3 ) 035502 (1-7) 2009.3
Language：English Publishing type：Research paper (scientific journal)
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Amorphous and microcrystalline GeC:H films prepared by magnetron sputtering Reviewed
N. Saito, H. Iwata, I. Nakaaki, K. Nishioka
physica status solidi (a) 206 ( 2 ) 238 - 242 2009.2
Language：English Publishing type：Research paper (scientific journal)
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Formation of micrometer-order-thick poly-Si films on textured glass substrates by flash lamp annealing of a-Si films prepared by catalytic chemical vapor deposition Reviewed
K. Ohdaira, T. Fujiwara, Y. Endo, K. Nishioka, H. Matsumura
Journal of Crystal Growth 311 ( 3 ) 769 - 772 2009.1
Language：English Publishing type：Research paper (scientific journal)
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A NOVEL THIN-FILM POLY-SI SOLAR CELLS FORMED ON A GLASS SUBSTRATE BY FLASH LAMP ANNEALING OF P-I-N AMORPHOUS SILICON FILMS PREPARED BY CATALYTIC CVD
K. Ohdaira, Y. Endo, T. Fujiwara, K. Shiba, H. Takemoto, K. Koyama, S. Nishizaki, Y. R. Jang, K. Nishioka, H. Matsumura
23rd European Photovoltaic Solar Ebergy Conference and Exhibition 2008.9
Language：English Publishing type：Research paper (international conference proceedings)
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Novel Stacked Nanodisk with Quantum Effect Fabricated by Defect-free Chlorine Neutral Beam Etching Reviewed
Chi-Hsien Huang, Makoto Igarashi, Kensuke Nishioka, Masaki Takeguchi, Yukiharu Uraoka, Takashi Fuyuki, Ichiro Yamashita, Seiji Samukawa
Appl. Phys. Express 1 084002 2008.8
Language：English Publishing type：Research paper (scientific journal)
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Antireflection subwavelength structure of silicon surface formed by wet process using catalysis of single nano-sized gold particle Reviewed
Kensuke Nishioka, Susumu Horita, Keisuke Ohdaira, Hideki Matsumura
Solar Energy Materials and Solar Cells 92 ( 8 ) 919 - 922 2008.8
Language：English Publishing type：Research paper (scientific journal)
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A New Silicon Quantum-Well Structure with Controlled Diameter and Thickness Fabricated with Ferritin Iron Core Mask and Chlorine Neutral Beam Etching Reviewed
Seiji Samukawa, Tomohiro Kubota, Chi-Hsien Huang, Takeshi Hashimoto, Makoto Igarashi, Kensuke Nishioka, Masaki Takeguchi, Yukiharu Uraoka, Takashi Fuyuki, Ichiro Yamashita
Appl. Phys. Express 1 074002 2008.6
Language：English Publishing type：Research paper (scientific journal)
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THIN FILM P-I-N POLY-SI SOLAR CELLS DIRECTLY CONVERTED FROM P-I-N A-SI STRUCTURES BY A SINGLE SHOT OF FLASH LAMP
Keisuke Ohdaira, Tomoko Fujiwara, Yohei Endo, Kazuhiro Shiba, Hiroyuki Takemoto, Shogo Nishizaki, Young Rae Jang, Kensuke Nishioka, Hideki Matsumura
Proc. 33rd IEEE Photovoltaic Specialists Conf. 2008.5
Language：English Publishing type：Research paper (international conference proceedings)
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Periodic arrays of submicron Si and Ni dots on SiO2 fabricated using linearly polarized Nd:YAG pulsed laser Reviewed
Kensuke Nishioka, Susumu Horita
Applied Physics A: Materials Science & Processing 91 ( 2 ) 235 - 240 2008.5
Language：English Publishing type：Research paper (scientific journal)
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Analysis of multicrystalline silicon solar cells by modified 3-diode equivalent circuit model taking leakage current through periphery into consideration Reviewed
Kensuke Nishioka, Nobuhiro Sakitani, Yukiharu Uraoka, Takashi Fuyuki
Solar Energy Materials and Solar Cells 91 ( 13 ) 1222 - 1227 2007.8
Language：English Publishing type：Research paper (scientific journal)
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Periodically Aligned Submicron Lines of Silicon and Nickel Fabricated using Linearly Polarized Nd:YAG Pulse Laser Reviewed
Kensuke Nishioka, Susumu Horita
Japanese Journal of Applied Physics 46 ( 7A ) 4154 - 4159 2007.7
Language：English Publishing type：Research paper (scientific journal)
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Surface modification of an amorphous Si thin film crystallized by a linearly polarized Nd:YAG pulse laser beam Reviewed
Susumu Horita, Hirokazu Kaki, Kensuke Nishioka
Japanese of Applied Physics 102 013501 2007.7
Language：English Publishing type：Research paper (scientific journal)
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Coulomb-staircase observed in silicon-nanodisk structures fabricated by low-energy chlorine neutral beams Reviewed
Tomohiro Kubota, Takeshi Hashimoto, Masaki Takeguchi, Kensuke Nishioka, Yukiharu Uraoka, Takashi Fuyuki, Ichiro Yamashita, Seiji Samukawa
Journal of Applied Physics 101 124301 2007.6
Language：English Publishing type：Research paper (scientific journal)
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Periodically Aligned Submicron Dots of Silicon and Nickel Fabricated by Irradiation with Linearly Polarized Nd:YAG Pulsed Laser Reviewed
Kensuke Nishioka, Susumu Horita
Japanese Journal of Applied Physics 46 ( 23 ) L556 - L558 2007.6
Language：English Publishing type：Research paper (scientific journal)
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Multireflection effect on formation of periodic surface structure on an Si film melting-crystallized by a linearly polarized Nd:YAG pulse laser beam Reviewed
Susumu Horita, Hirokazu Kaki, Kensuke Nishioka
Japanese Journal of Applied Physics 46 ( 6A ) 3527 - 3533 2007.6
Language：English Publishing type：Research paper (scientific journal)
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Effect of hydrogen plasma treatment on grain boundaries in polycrystalline silicon solar cell evaluated by laser-beam-induced current Reviewed
Kensuke Nishioka, Toshiki Yagi, Yukiharu Uraoka, Takashi Fuyuki
Solar Energy Materials and Solar Cells 91 ( 1 ) 1 - 5 2007.1
Language：English Publishing type：Research paper (scientific journal)
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Horita S., Nishioka K., Kaki H.
IDW/AD'05 - Proceedings of the 12th International Display Workshops in Conjunction with Asia Display 2005 ( 2 ) 1191 - 1194 2005.12
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：IDW/AD'05 - Proceedings of the 12th International Display Workshops in Conjunction with Asia Display 2005
In the Si film crystallized by a linearly polarized Nd:YAG laser beam, the grain boundaries are aligned periodically. This periodic structure is produced by the periodic beam energy density profile generated by interference between the coherent incident and high order diffracted beams. The effect of multiple reflection in the Si film was investigated theoretically on the surface structure of the crystallized film. The suitable thickness for this method was estimated by this theoretical analysis and verified experimentally.
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Nishioka K., Hagihara R., Nakagami H., Tanaka A., Uraoka Y., Fuyuki T.
Proceedings of the 3rd World Conference on Photovoltaic Energy Conversion C 2306 - 2309 2003.12
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Proceedings of the 3rd World Conference on Photovoltaic Energy Conversion
We have analyzed field-test data collected from grid-connected PV systems for residential houses in the Tokyo area from August 1999 to July 2000 in detail, focusing on module temperature. It was demonstrated that the PV systems operated in the wide temperature range, and that the module temperature range in which the PV systems operated differed greatly even for the same type of module due to the installation environment. Further, we have discussed the influence of module temperature on annual output energy quantitatively. These results indicate that it is very important to consider the temperature characteristics of solar cells and the operation temperature of modules.
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Analysis of triple-junction solar cell under concentration by spice
Nishioka K., Takamoto T., Nakajima W., Agui T., Kaneiwa M., Uraoka Y., Fuyuki T.
Proceedings of the 3rd World Conference on Photovoltaic Energy Conversion A 869 - 872 2003.12
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Proceedings of the 3rd World Conference on Photovoltaic Energy Conversion
The characteristics of multi-junction solar cell under concentration were evaluated by SPICE (Simulation Program with Integrated Circuit Emphasis). We developed the multi-unit model and analyzed the affect of the chromatic aberration and intensity distribution for the multi-junction cells. In the multi-unit model, the same numbers of units as grid numbers are installed for every electrode, and the units were connected each other with the lateral resistances. In order to obtain the generation current from each diode, we measured intensity of concentrated light through the pinhole using single-junction solar cells consisted of InGaP, GaAs and Ge as detectors. By using the multi-unit model, we could successfully calculate the electrical cell performances taking the chromatic aberration and intensity distribution into account, and the calculated value agreed well with the experimental value. The multi-unit model will be very useful for cell designs and performance analysis of the concentrator cells.
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Yamamoto Y., Ishikawa Y., Nishioka K., Uraoka Y., Fuyuki T.
Conference Record of the IEEE Photovoltaic Specialists Conference 235 - 238 2002.12
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Conference Record of the IEEE Photovoltaic Specialists Conference
Thin film single crystalline silicon solar cells were fabricated and minority carrier diffusion length was evaluated using two-dimensional simulation. Effective minority carrier diffusion length (L eff ) in 19μm-thickness cell was obtained as 19 μm by the surface photovoltage (SPV) method. Further, bulk minority carrier diffusion length (L b ) was estimated to over 50 μm from fitting for external quantum efficiency (EQE) using numerical simulation. In the case of L b ≥ cell thickness, L eff estimated from SPV was limited to the thickness of the cell, and L b could not be evaluated accurately. Therefore, fitting of EQE in the wide wavelength region by two-dimensional simulator was indispensable for accurate evaluation of minority carrier diffusion length in thin single crystalline silicon solar cells.