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)