Papers - NISHIOKA Kensuke
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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)