Papers - Araki Kenji
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Demonstration of the performance static low-concentration module using hybrid lens arrays Reviewed
Lee K.H., Daisuke S., Araki K., Yamada N., 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. We demonstrated a static (non-tracking) low concentration photovoltaic module that employs a new design paradigm that mixes two different types of the lens arrays. This design approach brings the annual optical collection efficiency closerto the theoretical upper hmitbutwith high manufacturabilityand scalabilhy, because this design paradigm gives more degree of freedom to optimize the overall efficiencies. We demonstrated that the module with the hybnd lens array is 2-%(absolute) more efficient than its single lens array counterparts at on-axis illumination. Also, the good match of the modeled and experimental incident-angle dependent module efficiency confirms the robustness of our fabrication process, showing the promise of achieving high annual collection efficiency of this module.
DOI： 10.1063/1.5124208
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Nuñez N., Vazquez M., Schilling R., Araki K., Algora C.
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. Qualification standards are one the driving forces for the commercialization and production of the Concentrator Photovoltaic (CPV) technology. After several years of preparation the Committee Draft of IEC 62787 has been finally submitted. The new standard IEC 62787 (Concentrator photovoltaic (CPV) solar cells and cell-on-carrier (CoC) assemblies - Qualification) fills the gap between the IEC TS 62789:2014 (Photovoltaic concentrator cell documentation) and the IEC 62108 Ed 2 (Concentrator photovoltaic (CPV) modules and assemblies - Design qualification and type approval). In the present article, apart from analyzing the objective, main guidelines, the innovative characteristics, and the life estimation from several tests of the qualification standard is also explained.
DOI： 10.1063/1.5124221
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Analysis for Radiation Degradation of Advanced Si Space Solar Cells
Yamaguchi M., Lee K.H., Araki K., Kojima N., Okuno Y., Imaizumi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 2377 - 2380 2019.6
Language：English Publishing type：Research paper (scientific journal) Publisher：Conference Record of the IEEE Photovoltaic Specialists Conference
© 2019 IEEE. Advanced Si solar cells such as passivated emitter, hetero-junction and back contact solar cells are expected to use as space solar cells. In this paper, efficiency potential of crystalline Si space solar cells is analyzed by considering external radiative efficiency (ERE), voltage and fill factor losses. Crystalline Si space solar cells have efficiency potential of more than 26% at AM0 by realizing ERE of 20% from about 0.2% and normalized resistance of less than 0.05 from around 0.15. Non-radiative recombination and resistance losses in Si space solar cells are also discussed. Radiation degradation of Si space solar cells is also analyzed. Potential of advanced Si solar cells such as passivated emitter, hetero-junction and back contact solar cells for space applications is discussed from point view of radiation degradation.
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Lee K.H., Sato D., Araki K., Yamada N., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 2519 - 2523 2019.6
Language：English Publishing type：Research paper (scientific journal) Publisher：Conference Record of the IEEE Photovoltaic Specialists Conference
© 2019 IEEE. We demonstrated a static (non-tracking) low concentration photovoltaic module that employs a new design paradigm that mixes two different types of the lens arrays. This design approach brings the annual optical collection efficiency closer to the theoretical upper limit but with high manufac-turability and scalability, because this design paradigm give more degree of freedom to optimize the overall efficiencies. We demonstrated that the module with the hybrid lens array is 2-%(absolute) more efficient than its single lens array counterparts at on-axis illumination. Also, the good match of the modeled and experimental incident-angle dependent module efficiency confirms the robustness of our fabrication process, showing the promise of achieving high annual collection efficiency of this module.
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Yamaguchi M., Lee K.H., Araki K., Kojima N., Masuda T., Kimura K., Satou A.
Conference Record of the IEEE Photovoltaic Specialists Conference 1724 - 1728 2019.6
Language：English Publishing type：Research paper (scientific journal) Publisher：Conference Record of the IEEE Photovoltaic Specialists Conference
© 2019 IEEE. Although photovoltaics (PV) are expected to contribute as major electricity and energy source, there are some important issues such as continuous development of PV RD and creation of new markets to be developed. This paper emphasizes acceleration of PV system installations in Japan in order to overcome difficulty of increasing nuclear energy. This paper also presents importance of high-efficiency, low cost and highly reliable solar cells and modules by overviewing efficiency potential of various solar cells including Si tandem solar cells. Our approaches to automobile application by using high-efficiency and low-cost solar cell modules are presented.
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Sato D., Lee K., Araki K., Masuda T., Yamaguchi M., Yamada N.
Progress in Photovoltaics: Research and Applications 27 ( 6 ) 501 - 510 2019.6
Language：English Publishing type：Research paper (scientific journal) Publisher：Progress in Photovoltaics: Research and Applications
© 2019 John Wiley & Sons, Ltd. A low-concentration static III-V/Si partial concentrator photovoltaic (CPV) module for area-limited car roofs was designed and experimentally demonstrated. The concentrator lens geometry was optimized for an incidence-angle dependency of annual global irradiance on a car-roof (horizontal-flat) surface by considering arbitrary car orientations. The designed lens with a geometrical concentration ratio of 3.5× for III-V triple-junction (3-junction) cells can collect 46.6% and 36.4% of the annual irradiation onto a III-V 3-juction and Si cells, respectively, which are located under the III-V cell. The module design was validated by indoor and outdoor tests using a prototype submodule. The results show that the present module can potentially achieve up to 27.3% annual module efficiency, as projected from the actual daily submodule efficiency of 20.8% assuming state-of-the-art record cell efficiency. Furthermore, the outdoor test on a real curved car roof demonstrated that the effect of the curved surface on the power generation performance is comparable with that of a conventional PV module.
DOI： 10.1002/pip.3124
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Lee K.H., Sato D., Araki K., Yamada N., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 255 - 259 2019.6
Language：English Publishing type：Research paper (scientific journal) Publisher：Conference Record of the IEEE Photovoltaic Specialists Conference
© 2019 IEEE. We demonstrated a static (non-tracking) low concentration photovoltaic module that employs a new design paradigm that mixes two different types of the lens arrays. This design approach brings the annual optical collection efficiency closer to the theoretical upper limit but with high manufacturability and scalability, because this design paradigm give more degree of freedom to optimize the overall efficiencies. We demonstrated that the module with the hybrid lens array is 2%(absolute) more efficient than its single lens array counterparts at on-axis illumination. Also, the good match of the modeled and experimental incident-angle dependent module efficiency confirms the robustness of our fabrication process, showing the promise of achieving high annual collection efficiency of this module.
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Ota Y., Masuda T., Araki K., Yamaguchi M.
Solar Energy 184 84 - 90 2019.5
Language：English Publishing type：Research paper (scientific journal) Publisher：Solar Energy
© 2019 International Solar Energy Society Photovoltaic (PV) panels mounted on vehicle surfaces could directly power automobiles in the future. However, accurate predictions of energy yield from PV systems will be required to quantify vehicle mileage and additional power requirements. Therefore, to model the energy generation of car roof PV systems, it is essential to define a meaningful and scientifically accurate method for measuring solar irradiance. We measure irradiance with five pyranometers fixed to a car body using a mobile multipyranometer array (MMPA). This paper discusses a new approach that focuses on the incidence angle distribution model of sunlight to account for direct and diffuse components, and reports on our irradiance measurements on a stationary car using the proposed system. We define the incidence angle regarding the vector components of sunlight and analyze a model for sunlight angle distribution. Our data show that the peak incidence angle as predicted by MMPA is larger than the peak incidence angle predicted based on the conventional method. Consequently, we conclude that an irradiance distribution model based on MMPA can be applied to effectively design automotive static concentrator PV systems.
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The potential for concentrator photovoltaics: A feasibility study in India Reviewed
Kamath H., Ekins-Daukes N., Araki K., Ramasesha S.
Progress in Photovoltaics: Research and Applications 27 ( 4 ) 316 - 327 2019.4
Language：English Publishing type：Research paper (scientific journal) Publisher：Progress in Photovoltaics: Research and Applications
© 2018 John Wiley & Sons, Ltd. India has aggressive plans for scaling up photovoltaic installations in the coming decades. Currently fixed tilt, flat plate crystalline silicon (c-Si) technology sets the standard for cost and performance and is both robust and relatively easy to deploy. Concentrator photovoltaics (CPV) systems have a different cost structure; using solar cells with the highest efficiencies, system efficiencies greater than 30% are possible, but the system is also more sensitive to meteorological conditions. India has a complex and varied atmosphere that prevents a straightforward comparison of technologies, and hence, in this paper, we use a computer model to simulate the power output from CPV systems located in locations in India where the Aerosol Robotic Network (AERONET) stations are based and additionally, in Bangalore where we have a CPV test station. We quantify the increased intermittency suffered by CPV systems that arises from the larger dynamic range in direct beam irradiance over global irradiance. Nevertheless, by calculating the target system costs required to attain a competitive levelized cost of electricity (LCOE), we find that CPV systems in some, but not all locations have the opportunity to compete against dual-axis tracked and inclined c-Si based PV in India.
DOI： 10.1002/pip.3099
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Performance Analysis and Fault Diagnosis Method for Concentrator Photovoltaic Modules Reviewed
Kamath H., Ekins-Daukes N., Araki K., Ramasesha S.
IEEE Journal of Photovoltaics 9 ( 2 ) 424 - 430 2019.3
Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Journal of Photovoltaics
© 2011-2012 IEEE. Concentrator photovoltaic (CPV) systems use high efficiency multi-junction solar cells with efficiencies >40%, but the module efficiency is often much lower. The increased complexity of a CPV module, with optics, receiver, and the tracker give an increased probability that faults will arise during the operational lifetime. In addition, a location like India has varied atmospheric conditions that further complicate the diagnosis of faults. It is therefore important to decouple effects due to the external environment (such as the atmosphere) from effects due to the degradation of the module. By applying a computer model to outdoor CPV test data in Bangalore, India, we have established a method to assess the performance of the CPV module and finally we present a method to diagnose faults in the module.
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Sato D., Lee K., Araki K., Yamaguchi M., Yamada N.
IEEE Journal of Photovoltaics 9 ( 1 ) 147 - 153 2019.1
Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Journal of Photovoltaics
© 2011-2012 IEEE. This paper describes the design and evaluation of a III-V/Si partial concentrator photovoltaic (CPV) module with a stacked structure comprising a highly transparent CPV module and a Si cell, which aims to maximize the power generation from global normal irradiation (GNI) by harvesting not only direct, but diffuse sunlight as well. The module structure was designed by considering the optical and heat transfer characteristics, and its performance was evaluated by outdoor and indoor tests using a prototype submodule with a geometrical concentration ratio of 100×. The submodule achieves diffuse sunlight transmission of over 80%, thus generating more power from diffuse sunlight. Under clear-sky condition, the submodule with a single-sided Si cell exhibits the maximum GNI-based module efficiency of 30.7%. The submodule with a bifacial Si cell further improves the power generation and tolerance to tracking error angle for various sunlight conditions.
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Lee K., Araki K., Yamaguchi M.
IEEE Access 7 97208 - 97215 2019
Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Access
© 2013 IEEE. Equivalent circuit network simulation is widely used in modeling solar cells in three dimensions. However, the computational time and numerical instability increases dramatically when the number of circuit element increases. This problem is exacerbated by increasing the number of junctions in the solar cells. We propose a downsampling algorithm to reduce the time complexity but retain reasonable accuracy within the appropriate parameter space of multi-junction solar cells. We also publish a full-featured software that implements this algorithm and the full circuit network simulation along with this paper.
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Review of recent progress in car-roof PVs for applications as an automobile energy source Reviewed
ARAKI Kenji, YAMAGUCHI Masafumi
Oyo Buturi 88 ( 2 ) 84 - 90 2019
Language：English Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Applied Physics
A car-roof photovoltaic has significant potential to change our society. With this technology, 70% of a car will be able to run on the solar energy collected by the solar panel on its roof. However, it is not a simple extension of conventional photovoltaic technology. This paper discusses what we need to do to achieve the goal of running a majority of cars on solar energy, after clarification of the differences from conventional photovoltaic technology.
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Ota Y., Masuda T., Araki K., Yamaguchi M.
Coatings 8 ( 12 ) 2018.12
Authorship：Lead author Language：English Publishing type：Research paper (scientific journal) Publisher：Coatings
© 2018 by the authors. For modeling the energy generation of three-dimensional car roof photovoltaic (PV) panels, it is essential to define a scientifically accurate method to model the amount of solar irradiance received by the panel. Additionally, the average annual irradiance incident on car roofs must be evaluated, because the PV module is often shaded during driving and when parked. The curve-correction factor, which is a unique value depending on the three-dimensional curved shape of the PV module, is defined in this paper. The curve-correction factor was calculated using a ray-trace simulator. It was found that the shape of the curved surface affected the curve-correction factor. The ratio of the projection area to the curved surface area of most car roofs is 0.85-0.95, and the annual curve-correction factor lies between 0.70 and 0.90. The annual irradiance incident on car roofs was evaluated using a mobile multipyranometer array system for one year (September 2017-August 2018). It is estimated that the effective annual solar radiation for curved PV modules is 2.53-3.52 kWh m-2/day.
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Verification of uncertainty in CPV's outdoor performance Reviewed
Saiki H., Sakai T., Araki K., Ota Y., Lee K.H., Yamaguchi M., Nishioka K.
2018 IEEE 7th World Conference on Photovoltaic Energy Conversion, WCPEC 2018 - A Joint Conference of 45th IEEE PVSC, 28th PVSEC and 34th EU PVSEC 949 - 953 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. Multi-junction cells have high efficiency but their performance ratio was less than the conventional single junction cell. One of the issues is lower outdoor performance in the outdoor operation conditions due to spectrum mismatch influenced by fluctuation of sun-height and atmospheric parameters. In this study, to predict the energy yield at an arbitrary point, firstly, we estimated the range of atmospheric parameter fluctuation that determines the spectrum from Bird's spectrum model using the DNI spectrum measured at University of Miyazaki. Furthermore, we examined the uncertainty of the outdoor performance of CPV system using the DNI spectrum resynthesized from the Monte Carlo method. As a result, when considering the atmospheric parameters, calculated values approached to the measured values and the uncertainty of outdoor performance was confirmed.
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Achieving High Efficiency Static Low-Concentration Photovoltaic Module Using Hybrid Lens Arrays
Lee K.H., Araki 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 905 - 908 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. We propose a new design paradigm of static low concentration photovoltaics for III-V or silicon solar cells. Although static/non-tracking low concentrator optics has been studied extensively, most of these designs are either difficult to implement or low optical efficiency. In this work, we present a design that uses lens array that mixes two different optics, giving more degrees of freedom to optimize the optics and the size of solar cells. This design approach brings the optical efficiency closer to the theoretical upper limit while maintaining manufacturability and scalability. Although the design example presented in this work is aimed to mount on sloped surface, this can be also applied to the building integrated photovoltaics or on car-roof.
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Sato D., Lee K., Araki K., Masuda T., Yamaguchi M., Yamada N.
2018 IEEE 7th World Conference on Photovoltaic Energy Conversion, WCPEC 2018 - A Joint Conference of 45th IEEE PVSC, 28th PVSEC and 34th EU PVSEC 954 - 957 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. This paper describes the design and evaluation of a low-concentration static III-V/Si partial CPV module that aims to maximize the power generation in the limited car-rooftop area by harvesting full global sunlight. The concentrator lens was designed considering the incident angle dependence of annual global irradiance on the car-rooftop (horizontal flat) surface. The fundamental characteristics were investigated by optical simulation and indoor test using a prototype submodule with a geometrical concentration ratio of 3.5×. The designed lens can collect 46.6% and 36.4% of the annual solar irradiation onto triple-junction and Si cells, respectively, achieving the annual electricity yield which is equivalent to 30% efficiency flat PV module.
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Analysis for efficiency potential of crystalline Si solar cells Reviewed
Yamaguchi M., Lee K., Araki K., Kojima N., Ohshita Y.
Journal of Materials Research 33 ( 17 ) 2621 - 2626 2018.9
Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Materials Research
© 2018 Materials Research Society. Efficiency potential of crystalline Si solar cells is analyzed by considering external radiative efficiency (ERE), voltage, and fill factor losses. Crystalline Si solar cells have an efficiency potential of more than 28.5% by realizing ERE of 20% from about 5% and normalized resistance of less than 0.05 from around 0.1. Nonradiative recombination losses in single-crystalline and multicrystalline Si solar cells are also discussed. Especially, nonrecombination and resistance losses in multicrystalline Si solar cells are shown to be higher than those of single-crystalline cells. Importance of further improvement of minority-carrier lifetime in crystalline Si solar cells is suggested for further improvement of crystalline Si solar cells. High efficiency of more than 28.5% will be realized by realizing high minority-carrier lifetime of more than 30 ms. Key issues for those ends are reduction in carbon concentration of less than 1 × 1014 cm-3, oxygen precipitated and dislocations even in single-crystalline Si solar cells, and reduction in dislocation density of less than 3 × 103 cm-2 in multicrystalline Si solar cells.
DOI： 10.1557/jmr.2018.262
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Lee K., Araki K., Kojima N., Yamaguchi M.
AIP Conference Proceedings 2012 2018.9
Language：English Publishing type：Research paper (scientific journal) Publisher：AIP Conference Proceedings
© 2018 Author(s). We proposed a low-profile static low-concentration optics design paradigm for building-integrated photovoltaics or as alternative of flat PV panels. Based on the measurement results of our prototype, this design could reach more than 80% on-axis optical efficiency and more than 60% collection efficiency over an annual solar insulation, with a concentration of around 3x. The result is approaching the analytical maximum of non-tracking concentrator derived in previous study.
DOI： 10.1063/1.5053514
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Analysis for efficiency potential of high-efficiency and next-generation solar cells Reviewed
Yamaguchi M., Lee K., Araki K., Kojima N., Yamada H., Katsumata Y.
Progress in Photovoltaics: Research and Applications 26 ( 8 ) 543 - 552 2018.8
Language：English Publishing type：Research paper (scientific journal) Publisher：Progress in Photovoltaics: Research and Applications
Copyright © 2017 John Wiley & Sons, Ltd. This paper overviews photovoltaic R&D projects in Japan. Recently, world-record and second highest efficiencies of various types of solar cells have been demonstrated under the New Energy and Industrial Technology Development Organization Project: 44.4% (under concentration) and 37.9% (under 1 sun) InGaP/GaAs/InGaAs inverted metamorphic 3-junction solar cells by Sharp, 26.7% single crystalline Si heterojunction back-contact solar cell by Kaneka, 22.3% copper indium gallium selenide solar cell by Solar Frontier, a-Si/μc-Si/μc-Si thin-film triple-junction solar cell with stabilized efficiency of 14.0% by AIST, 11.9% dye-sensitized solar cell by Sharp, and 11.2% organic solar cell by Toshiba. This paper also presents efficiency potential of high-efficiency and next-generation solar cells analyzed by considering external radiative efficiency, open-circuit voltage loss, and fill factor loss. Efficiency potential of crystalline Si, GaAs, III-V compound 3-junction and 5-junction, CIGSe, CdTe, CZTS(Se), multiquantum well, and quantum dot and perovskite solar cells is shown to be 28.5%, 29.7%, 40%, 43%, 26.5%, 26.5%, 20%, 25.8%, and 24.9% under 1 sun, respectively.
DOI： 10.1002/pip.2955