Papers - Araki Kenji
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Araki K., Ota Y., Nagaoka A., Nishioka K.
Energies 16 ( 11 ) 2023.6
Authorship：Lead author 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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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
© 2020 American Institute of Physics Inc.. All rights reserved. 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
© 2020 American Institute of Physics Inc.. All rights reserved. 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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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 ) 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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Measurement and modeling of 3D solar irradiance for vehicle-integrated photovoltaic Reviewed
Araki K., Ota Y., Yamaguchi M.
Applied Sciences (Switzerland) 10 ( 3 ) 872 2020.2
Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Sciences (Switzerland)
© 2020 by the author. The energy yield of vehicle-integrated photovoltaics (VIPV) differs from that of standard photovoltaics (PV). It is mainly by the difference of the solar irradiance onto the car roof and car bodies as well as its curved shape. Both meaningful and practical modeling and measurement of solar irradiance for VIPV need to be established, rather than the extension of the current technologies. The solar irradiance is modeled by a random distribution of shading objects and car orientation with the correction of the curved surface of the PV modules. The measurement of the solar irradiance onto the car roof and car body is done using five pyranometers in five local axes on the car for one year. The measured dynamic solar irradiance onto the car body and car roof is used for validation of the solar irradiance model in the car.
DOI： 10.3390/app10030872
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Araki K., Ota Y., Saiki H., Tawa H., Nishioka K., Yamaguchi M.
Applied Sciences (Switzerland) 9 ( 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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Araki K., Sato D., Masuda T., Lee K., Yamada N., Yamaguchi M.
AIP Conference Proceedings 2149 2019.8
Authorship：Lead author Language：English Publishing type：Research paper (scientific journal) Publisher：AIP Conference Proceedings
© 2019 American Institute of Physics Inc.. All rights reserved. With this car-roof PV, 70 % of passenger's may be able to run by solar energy. The potential of the market size is 50 GW/year. However, it is not an easy task to meet the requirement of the main component of EV and the creation of the massive market. It is also apparent that the market will be small as far as we only try to apply the conventional crystalline Si cells. The CPV technology with high power conversion efficiency and capable of coloring and covering on the threedimensional curved surface is suitable for this market. The static CPV is useful for this application with a better collection of diffused sunlight. One of the problems is the spectrum mismatching. However, this issue is easily solved by adjustment of the bandgap of the bottom cell.
DOI： 10.1063/1.5124188
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Araki K., Ota Y., Lee K.H., Nishioka K., Yamaguchi M.
AIP Conference Proceedings 2149 2019.8
Language：English Publishing type：Research paper (scientific journal) 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 (scientific journal) 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.H., Nishioka K., Yamaguchi M.
2019 18th International Conference on Optical Communications and Networks, ICOCN 2019 2019.8
Language：English Publishing type：Research paper (scientific journal) 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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Alignment Tolerance Control of the Micro CPV Array Using Monte Carlo Methods
Araki K., Lee K.H., Hayashi N., Ichihashi K., Kanayama S., Inohara T., Morita Y., Takase M., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 202 - 209 2019.6
Language：English Publishing type：Research paper (scientific journal) Publisher：Conference Record of the IEEE Photovoltaic Specialists Conference
© 2019 IEEE. Micro CPV is a promising technology for reducing high-precision assembly cost while making use of the high efficiency of CPV. A production method is often taken to manufacture small size modules with high accuracy, high homogeneity, low cost, and to compile them. There is a concern that the performance of the large-area panel may deteriorate due to accuracy in the assembly. We did the Monte Carlo analysis for simulate assemble error. It could successfully define inspection conditions and tolerance control thresholds with consideration of the worst-case of the tracking errors. With proper but reasonable inspections (component acceptance and alignment accuracy test), it is possible to collect micro-CPV units to a reasonable-size of the CPV panel keeping more than 90 % of the output even with the worst-case installation and tracking errors. This approach can be expanded to the analysis of impact by the partial shading of the lens that has a significant impact on the performance of CPV.
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Araki K., Ota Y., Lee K.H., Yamada N., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 1584 - 1591 2019.6
Language：English Publishing type：Research paper (scientific journal) Publisher：Conference Record of the IEEE Photovoltaic Specialists Conference
© 2019 IEEE. Curved photovoltaic, typically using flexible one receives different irradiation from the sunlight. The energy yield is often overestimated by ignoring local cosine loss and other losses related to the curvature of the PV surface. Although the formula to some extent varies by the type of the curved surface, it is modeled by the curve-correction factor from the flat-plate conditions. The curve correction factor is calculated either geometrical calculation or the numerical ray-tracing simulation. In these proceedings, the one by Monte Carlo method (Ray-tracing simulation) is discussed. First, the incident angle the sunlight affected by the orientation (random orientation if necessary), shading by surrounding structures (randomly distributed), climate pattern, and both direct and diffused sunlight from a regional database, was calculated. Second, the absorbed flux onto the curved module surface was calculated using random rays by the above distribution of the sunlight. Third, the regional influences onto the energy generation of the curved PV panel were discussed. The energy yield of the curved PV drops significantly by the increase of the curvature and incident angle distribution affected by latitude, climate pattern, and shading environment.
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Araki K., Lee K.H., Masuda T., Hayakawa Y., Yamada N., Ota Y., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 1218 - 1225 2019.6
Language：English Publishing type：Research paper (scientific journal) Publisher：Conference Record of the IEEE Photovoltaic Specialists Conference
© 2019 IEEE. Solar panels used for EV charging stations and car-roof PV are often partially shaded and lead to substantial energy loss. It is known that this mismatching loss can be reduced by increasing the number of parallel strings. First, a probability model was developed using a one-year solar irradiance monitoring around the car body in 5 directions. The developed model successfully matched to the measured solar resource in each direction and succeeded to quantify the probability of the partial shading on the car. Another related issue of the inherent mismatching loss of the car-roof PV is non-uniform illumination caused by the curved shape of the panel. This can also be modeled by ray-tracing simulation. Then, we calculated the PV output affected by mismatching due to various sunlight patterns and partial shade patterns by Monte Carlo method. It was found that the average efficiency asymptotically approached 1 - 1 / N (N is the number of strings). We also examined the relationship between partial shade quantity and power generation loss in a 30 kW solar system array and verified the above model.
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Araki K., Ji L., Kelly G., Agudo E., Anton I., Baudrit M., Carr A., Herrero R., Kurtz S., Liu Z., Limpinsel M., Lu Z., Pravettoni M., Robusto P., Tobita H., Wu Q., Wu Z., Yoon S., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 2722 - 2729 2019.6
Language：English Publishing type：Research paper (scientific journal) Publisher：Conference Record of the IEEE Photovoltaic Specialists Conference
© 2019 IEEE. A car-roof photovoltaic (PV) has significant potential. The activities of international standardization through a series of web meetings have been done by 51 volunteer scientists and engineers from 15 different countries with a good mixture of scientists, manufacturers, and testing laboratories. Specifically, it covered (1) Irradiance modeling onto the car-roof; (2) Curve correction of the PV output; (3) Quantification of partial shading loss; (4) Performance testing conditions; (5) Effective solar resource on the car-roof impacted by shadows of surrounding buildings; (6) Environmental testing conditions.
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Design of the Micro-Köhler Concentrator Optics for CPV Application
Araki K., Lee K.H., Hayashi N., Ichihashi K., Kanayama S., Inohara T., Morita Y., Takase M., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 196 - 201 2019.6
Language：English Publishing type：Research paper (scientific journal) Publisher：Conference Record of the IEEE Photovoltaic Specialists Conference
© 2019 IEEE. Micro CPV is a promising technology for reducing high-precision assembly cost while making use of the high efficiency of CPV. However, the requirement of the installation and tracking accuracy remains the same. A production method is often taken to manufacture small size modules with high accuracy, high homogeneity, low cost, and to compile them. There is a concern that the performance of the large-area panel may deteriorate due to accuracy in the assembly. A micro-Köhler concentrator optics was designed suitable to the micro CPV modules, and the designed acceptance angle (90 % power point) reached 1.8 degrees with the 500 x axially symmetrical (truncated to square) primary plano-convex lens.
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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
© 2018 IEEE. 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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Araki K., Ota Y., Lee K.H., Nishioka K., 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 1661 - 1666 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
© 2018 IEEE. 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. Partially Radiativecoupling multi-junction solar cells were proposed, and optimization work was done. 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.
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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
© 2018 Author(s). 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
© 2018 Author(s). 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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The possibility of the static LCPV to mechanical-stack III-V//Si module Reviewed
Araki K., Lee K., Yamaguchi M.
AIP Conference Proceedings 2012 2018.9
Language：English Publishing type：Research paper (scientific journal) Publisher：AIP Conference Proceedings
© 2018 Author(s). For further reduction of the cost of the III-V//Si cell, a 4-terminal III-V//Si partial concentrator cell was proposed. A Monte Carlo analysis showed that the 4-terminal configuration had an advantage under high aerosol density. The partial concentrator optics of 1.5x of concentration ratio was optimized, and the angular loss was 1% of the annual energy yield. The mono module efficiency was 27.08%. Moreover, corresponding cell efficiency was 31.03%. Although the area of the top cell in 2/3, the efficiency is the almost same as the non-concentration operation. The contribution from the bottom Si cell increases and reaches nearly 6 %, whereas regular Si cell contribution is around 4 %. The angular loss due to concentrator optics is almost ignored.
DOI： 10.1063/1.5053540