Papers - Araki Kenji
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Anti-soiling layer coarted on PMMA Fresnel lens for concentrator photovoltaic modules Reviewed
Nishioka K., Nabemoto K., Sakurada Y., Ota Y., Takami K., Nagai H., Araki K.
Conference Record of the IEEE Photovoltaic Specialists Conference 003332 - 003334 2011.12
Language：English Publishing type：Research paper (scientific journal) Publisher：Conference Record of the IEEE Photovoltaic Specialists Conference
An anti-soiling layer was coated on the PMMA substrates. The anti-soiling layer was prepared by coating the inorganic/organic nano-graded intermediate layer (Ube-Nitto Kasei Co., Ltd.) and photocatalytic surface layer including modified WO 3 (ILUMIO®, Sumitomo Chemical Co., Ltd.) and partial hydrolyzed tetraethylorthosilicate (Wako Pure Chemical Industries, Ltd.). After 6 months, the reduction rate of photocurrent without anti-soiling coat was 7.5%. On the other hand, that with anti-soiling coat could be suppressed to 3%. The experimental environment of the exposure site is clean, and there is a lot of rainfall. It is considered that the effect of the anti-soiling coat must be more significant if CPV systems are installed in dusty areas. © 2011 IEEE.
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Lightning test for concentrator photovoltaic system Reviewed
Tamura K., Araki K., Kumagai I., Nagai H.
Conference Record of the IEEE Photovoltaic Specialists Conference 000996 - 000998 2011.12
Language：English Publishing type：Research paper (scientific journal) Publisher：Conference Record of the IEEE Photovoltaic Specialists Conference
This paper describes the results of the lightning test for CPV system. The CPV system is provided with a tracking device. For 14kW system, the entire aperture area is 75 m 2 and its height is approximately 10 m. This is relatively tall structure and subject to receive lightning damage. The IEC62305 standard describes the durability of CPV modules against lightning strike effect. Our test revealed that lightning current passed through the module's aluminum chassis and flowed directly into the ground. Module IV measurement was performed, and no degradation or change was observer before and after the lightning test. © 2011 IEEE.
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Present and future of high efficiency multi-junction solar cells Reviewed
Yamaguchi M., Takamoto T., Araki K., Imaizumi M., Kojima N., Ohshita Y.
Optics InfoBase Conference Papers 2011.12
Language：English Publishing type：Research paper (scientific journal) Publisher：Optics InfoBase Conference Papers
This paper reviews our research activities for III-V compound multi-junction (MJ) solar cells and recent R&D topics on concentrator MJ solar cells under the NEDO's R&D Project on Innovative Solar Cells initiated since 2008. The conversion efficiency of InGaP/(In)GaAs/InGaAs triple-junction solar cells has been improved to 35.8% (1-sun, AM1.5G) and 42.1% (230-suns) as a result of proposing double-hetero wide-band-gap tunnel junctions, understanding dislocation behavior in the lattice mismatched system and inverted epitaxial layer structure. We have contributed to industrialization of InGaP-based multi-junction solar cell for space use in Japan. The authors have also shown great potential of concentrator PV for terrestrial applications by developing concentrator 3-junction solar cell modules (area of 5,500cm2 for 550suns use) with an efficiency of 31.5%. Now, we are challenging higher efficiency toward 50% under the NEDO's Innovative R&D Project. © OSA/ CLEO 2011.
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Long-term performance estimation of a 500X concentrator photovoltaic system Reviewed
Kemmoku Y., Oke S., Araki K.
30th ISES Biennial Solar World Congress 2011, SWC 2011 1 710 - 715 2011.12
Language：English Publishing type：Research paper (scientific journal) Publisher：30th ISES Biennial Solar World Congress 2011, SWC 2011
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Present and future of high efficiency multi-junction solar cells Reviewed
Yamaguchi M., Takamoto T., Araki K., Imaizumi M., Kojima N., Ohshita Y.
2011 Conference on Lasers and Electro-Optics: Laser Science to Photonic Applications, CLEO 2011 2011.9
Language：English Publishing type：Research paper (scientific journal) Publisher：2011 Conference on Lasers and Electro-Optics: Laser Science to Photonic Applications, CLEO 2011
This paper reviews our research activities for III-V compound multi-junction (MJ) solar cells and recent R&D topics on concentrator MJ solar cells under the NEDO's R&D Project on Innovative Solar Cells initiated since 2008. The conversion efficiency of InGaP/(In)GaAs/InGaAs triple-junction solar cells has been improved to 35.8% (1-sun, AM1.5G) and 42.1% (230-suns) as a result of proposing double-hetero wide-band-gap tunnel junctions, understanding dislocation behavior in the lattice mismatched system and inverted epitaxial layer structure. We have contributed to industrialization of InGaP-based multi-junction solar cell for space use in Japan. The authors have also shown great potential of concentrator PV for terrestrial applications by developing concentrator 3-junction solar cell modules (area of 5,500cm2 for 550suns use) with an efficiency of 31.5%. Now, we are challenging higher efficiency toward 50% under the NEDO's Innovative R&D Project. © 2011 OSA.
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Analysis of shadow by HCPV panels for agricilture applications Reviewed
Araki K., Akisawa A., Kumagai I., Nagai H.
Conference Record of the IEEE Photovoltaic Specialists Conference 2994 - 2997 2010.12
Language：English Publishing type：Research paper (scientific journal) Publisher：Conference Record of the IEEE Photovoltaic Specialists Conference
This paper discusses optical impact to the cultivation area with comparison of flat-plate PV and tracking PV - typically HCPV. Sometimes the PV area is covered by concrete, asphalt or graves for suppression of weeds. In this case, the atmosphere may be better but the PV owner will have to pay additional land cost preparation. Another aspect is the land utilization. This complies that massive unused land space is required. In this situation, it is reasonable to think of utilizing PV-uncovered area for agriculture. This paper discusses the space factor of the PV field by comparison of measured and calculated results as well as possibility of utilizing the land underneath PV array by agriculture. The farmland equipped with high-pole CPV has about 2 times more cultivated land, and the minimum illumination level of the cultivated land is around 2 times, the total sunlight energy to the farming land is almost 3 times. The PV output per lost cultivated land is about 2 times. © 2010 IEEE.
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What is the most appropriate and practical index to represent spectrum sensitivity of CPV? Reviewed
Araki K.
AIP Conference Proceedings 1277 205 - 208 2010.11
Language：English Publishing type：Research paper (scientific journal) Publisher：AIP Conference Proceedings
Different from crystalline silicon solar cells, CPV using III-V multi-junction cells does not receive great influences from temperature, rather receives from solar spectrum. Some rating values related to spectrum sensitivity are needed both for the label of modules and the energy rating. Generally, an accurate model needs measurement of many parameters, which is not always accurate and requires complicated calculations. First, input parameter should be common and easy to measure. This simplicity is important for repeatability among manufactures and testing labs. Second, input parameter is not vector but scalar value. In this regards, data set from direct solar spectrum is not appropriate. Third, output parameter that describes spectrum sensitivity is a single value. The method proposed by this paper is energy or capacity factor is expressed by quadric function of DNI. © 2010 American Institute of Physics.
DOI： 10.1063/1.3509190
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A new simple model of direct spectral irradiance with easily observable atmospheric parameters Reviewed
Oke S., Fukushige N., Kemmoku Y., Takikawa H., Sakakibara T., Araki K.
IEEJ Transactions on Electrical and Electronic Engineering 5 ( 5 ) 548 - 552 2010.9
Language：English Publishing type：Research paper (scientific journal) Publisher：IEEJ Transactions on Electrical and Electronic Engineering
Direct irradiance and direct spectral irradiance were measured for 16 months along with other basic atmospheric parameters. The direct irradiance changed smoothly on a clear day and fluctuated on a fair day. Then, we considered the possibility of a new, simple model of direct spectral irradiance expressed with fewer atmospheric parameters and applicable for even fair days. This new model, called DISPEC, can calculate the direct spectral irradiance from basic atmospheric parameters for wavelengths >400 nm. In DISPEC, the ozone absorption was ignored and the thin cloud effect was taken into account as a new parameter, which was considered to be proportional to the direct irradiance, instead of aerosol parameters. The performance of DISPEC was then compared with that of a well-known model of SPCTRAL2. Although the calculation results by SPCTRAL2 exhibited considerable error, especially in visible wavelength range on a fair day, those calculated using DISPEC showed good agreement with observed data on both clear and fair days. © 2010 Institute of Electrical Engineers of Japan.
DOI： 10.1002/tee.20571
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30 kW concentrator photovoltaic system using dome-shaped Fresnel lenses. Reviewed
Araki K, Yano T, Kuroda Y
Optics express 18 ( 9 ) A53 - 63 2010.4
Language：English Publishing type：Research paper (scientific journal)
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Nishimura A., Hayashi Y., Tanaka K., Hirota M., Kato S., Ito M., Araki K., Hu E.
Applied Energy 87 ( 9 ) 2797 - 2807 2010
Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Energy
In this study, the environmental load of photovoltaic power generation system (PV) during its life cycle and energy payback time (EPT) are evaluated by LCA scheme. Two hypothetical case studies in Toyohashi, Japan and Gobi dessert in China have been carried out to investigate the influence of installation location and PV type on environmental load and EPT. The environmental load and EPT of a high-concentration photovoltaic power generation system (hcpV) and a multi-crystalline silicon photovoltaic power generation system (mc-Si PV) are studied. The study shows for a PV of 100MW size, the total impacts of the hcpV installed in Toyohashi is larger than that of the hcpV installed in Gobi desert by 5% without consideration of recycling stage. The EPT of the hcpV assumed to be installed in Gobi desert is shorter than EPT of the hcpV assumed to be installed in Toyohashi by 0.64 year. From these results, the superiority to install PV in Gobi desert is certificated. Comparing with hcpV and mc-Si PV, the ratio of the total impacts of mc-Si PV to that of hcpV is 0.34 without consideration of recycling stage. The EPT of hcpV is longer than EPT of mc-Si PV by 0.27 year. The amount of global solar radiation contributing to the amount of power generation of mc-Si PV is larger than the amount of direct solar radiation contributing to the amount of power generation of hcpV by about 188 kW h/(m2 year) in Gobi desert. Consequently, it appears that using mc-Si PV in Gobi desert is the best option. © 2009 Elsevier Ltd. All rights reserved.
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Low-Concentration Linear-Array Photovoltaic System with Two-axis Sun Tracking Reviewed
OKE Shinichiro, ICHIKAWA Naoki, TAKIKAWA Hirofumi, SAKAKIBARA Tateki, ARAKI Kenji
IEEJ Transactions on Power and Energy 129 ( 9 ) 1154 - 1155 2009.10
Language：English Publishing type：Research paper (scientific journal) Publisher：The Institute of Electrical Engineers of Japan
In a concentrator photovoltaic (PV) system, high concentration causes a decrease of electrical output, since the temperature of the PV cell increases. A linear-array photovoltaic system (LAPS) with a relatively low concentration using a cylindrical mirror was developed. In this system, the sunlight was concentrated on a linearly-arrayed PV system with 7 mono-crystalline silicon PV modules. The LAPS was mounted on a two-axis sun-tracker system. The electrical efficiency was approximately 11% under typical operating conditions.
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Spectrometric outdoor characterization of CPV modules using isotype monitor cells Reviewed
Peharz G., Siefer G., Araki K., Bett A.
Conference Record of the IEEE Photovoltaic Specialists Conference 2008.12
Language：English Publishing type：Research paper (scientific journal) Publisher：Conference Record of the IEEE Photovoltaic Specialists Conference
In this paper we present a method to investigate the impact of the solar spectrum on the output parameters of a CPV module equipped with triple-junction solar cells. The changes of the sun's spectrum were monitored by using calibrated isotype solar cells. A correlation of the CPV module outdoor performance to changes in the sun spectrum has been determined. Experimental results of the spectral impact on the current of a Daido Steel CPV module are presented. Finally, a correction method is applied in order to derive the module's current under reference spectral conditions. © 2008 IEEE.
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Present and future of super high efficiency multi-junction solar cells Reviewed
Yamaguchi M., Takamoto T., Araki K.
Proceedings of SPIE - The International Society for Optical Engineering 6889 2008.3
Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of SPIE - The International Society for Optical Engineering
While single-junction solar cells may be capable of attaining AM1.5 efficiencies of up to 29%, multi-junction (MJ, Tandem) III-V compound solar cells appear capable of realistic efficiencies of up to 50% and are promising for space and terrestrial applications. In fact, the InGaP/GaAs/Ge triple-junction solar cells have been widely used for space since 1997. In addition, industrialization of concentrator solar cell modules using III-V compound MJ solar cells have been announced by some companies. This paper presents principles and key issues for realizing high-efficiency MJ solar cells, issues relating to development and manufacturing, and applications for space and terrestrial uses.
DOI： 10.1117/12.784117
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Novel materials for high-efficiency III-V multi-junction solar cells Reviewed
Yamaguchi M., Nishimura K.I., Sasaki T., Suzuki H., Arafune K., Kojima N., Ohsita Y., Okada Y., Yamamoto A., Takamoto T., Araki K.
Solar Energy 82 ( 2 ) 173 - 180 2008.2
Language：English Publishing type：Research paper (scientific journal) Publisher：Solar Energy
As a result of developing wide bandgap InGaP double hetero structure tunnel junction for sub-cell interconnection, InGaAs middle cell lattice-matched to Ge substrate, and InGaP-Ge heteroface structure bottom cell, we have demonstrated 38.9% efficiency at 489-suns AM1.5 with InGaP/InGaP/Ge 3-junction solar cells by in-house measurements. In addition, as a result of developing a non-imaging Fresnel lens as primary optics, a glass-rod kaleidoscope homogenizer as secondary optics and heat conductive concentrator solar cell modules, we have demonstrated 28.9% efficiency with 550-suns concentrator cell modules with an area of 5445 cm2. In order to realize 40% and 50% efficiency, new approaches for novel materials and structures are being studied. We have obtained the following results: (1) improvements of lattice-mismatched InGaP/InGaAs/Ge 3-junction solar cell property as a result of dislocation density reduction by using thermal cycle annealing, (2) high quality (In)GaAsN material for 4- and 5-junction applications by chemical beam epitaxy, (3) 11.27% efficiency InGaAsN single-junction cells, (4) 18.27% efficiency InGaAs/GaAs potentially modulated quantum well cells, and (5) 7.65% efficiency InAs quantum dot cells. © 2007 Elsevier Ltd. All rights reserved.
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Evaluation of the Output Fluctuation of a Grid-connected Concentrator Photovoltaic System Reviewed
KEMMOKU Yoshishge, ARAKI Kenji, HIRAMATSU Masao, MIYAZAKI Yoshinori
2007 361 - 364 2007.10
Language：English Publishing type：Research paper (scientific journal)
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Influence of Yellow Sand to Generated Electricity of Concentrator PV System Reviewed
OKE Shinichiro, TAKIKAWA Hirofumi, KEMMOKU Yoshishige, ARAKI Kenji
2007 365 - 368 2007.10
Language：English Publishing type：Research paper (scientific journal)
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Photoluminescence analysis of intragrain defects in multicrystalline silicon wafers for solar cells Reviewed
Sugimoto H., Araki K., Tajima M., Eguchi T., Yamaga I., Dhamrin M., Kamisako K., Saitoh T.
Journal of Applied Physics 102 ( 5 ) 2007.9
Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Applied Physics
Structures of intragrain defects were investigated by photoluminescence (PL) mapping tomography in multicrystalline silicon wafers for solar cells. PL dark patterns were observed in short minority carrier diffusion length regions, and we confirmed that the patterns came from the intragrain defects. The tomography revealed that the defects have planelike structures extended to the crystal growth direction. We also found that the growth conditions affect the structures of the defects: slower solidification leads to larger defects with lower density. Origins of the defects were analyzed by low-temperature PL spectroscopy, electron backscatter diffraction pattern measurement and etch-pit observation. We concluded that the defects are metal contaminated dislocation clusters which originate from small-angle grain boundaries. © 2007 American Institute of Physics.
DOI： 10.1063/1.2776003
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Concentrator solar cell modules and systems developed in Japan Reviewed
Yamaguchi M., Araki K., Takamoto T.
Springer Series in Optical Sciences 130 321 - 340 2007.8
Language：English Publishing type：Research paper (scientific journal) Publisher：Springer Series in Optical Sciences
Dissemination of photovoltaic (PV) systems has advanced, and solar cell module production has also significantly increased in Japan as a result of R&D programs such as the New Sunshine Project under the Ministry of Economy, Trade and Industry (METI), Residential PV System Dissemination Program, as well as others. Figure 15.1 shows Japanese cumulative installed capacity of PV systems. The total installed capacity of PV systems in 2004 reached 268.8MW and the cumulative installed capacity recorded 1128.2MW (over 1-GW level). The PV market in Japan is working toward a target of 4.82GW by 2010. As a result of discussion at the Committee for the 2030 PV Road Map in Japan organized by the New Energy and Industrial Technology Development Organization (NEDO) and METI, we also expect about 100-GW cumulative installed capacity [1], about 10% of Japanese electricity consumption, by 2030. The rapid growth in the PV market in recent years has been driven by the rooftop installations in the range 3-5 kWp; however, a market for larger PV systems is beginning to emerge, and in 2003 more than 20 systems of over 450kWp in size were commissioned in Europe and the U.S., with an installed capacity of 26MWp [2]. In addition, large-scale PV systems are necessary to develop in order to realize installation targets of PV systems shown in PV road maps. These facts suggest that concentrating PV systems can play a very important role for a growing PV market and a largescale productions of PV systems when cost-effectiveness against flat-plate arrays is demonstrated. © 2007 Springer-Verlag Berlin Heidelberg.
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Recent and future trends in PV technology Reviewed
Araki K., Beneking C., Faiman D., Gigliucci G., Paletta F.
Energy from the Desert: Very Large Scale Photovoltaic Systems: Socio-economic, Financial, Technical and Environmental Aspects 63 - 77 2007.1
Language：English Publishing type：Research paper (scientific journal) Publisher：Energy from the Desert: Very Large Scale Photovoltaic Systems: Socio-economic, Financial, Technical and Environmental Aspects
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Araki K., Kondo M., Uozumi H., Ekins-Daukes N., Egami T., Hiramatsu M., Miyazaki Y., Yamaguchi M.
Solar Energy Materials and Solar Cells 90 ( 18-19 ) 3320 - 3326 2006.11
Language：English Publishing type：Research paper (scientific journal) Publisher：Solar Energy Materials and Solar Cells
A new concentrator receiver containing a 7 mm×7 mm 3J concentrator solar cell with a 37.4% peak efficiency was developed. The receiver design includes a homogenizer, heat-handling (epoxy lamination) technologies and a low-resistance soldered connection and can be applied to various concentrator optics, including dish systems. The outdoor efficiency with a combination of a plastic Fresnel lens, made by low-cost injection molding, reached 27% on a hot summer day under 35.0 °C ambient temperature without additional cooling. With this newly developed receiver, mechanical engineers will be able to design their own concentrator module suitable for their environment, using their mechanical knowledge and local industrial resources. A 400X and 7056 cm2 concentrator module was fabricated with 36 concentrator receivers connected in series and the same number of newly developed dome-shaped, non-imaging Fresnel lenses. The power rating was 200 Wp. The peak outdoor efficiency on a clear sky day was 26.8±1.5%. The integrated efficiency over the course of the day was 25.3±1.4%. This is the highest module efficiency that has been achieved using a practical module size and electrical rating. © 2006 Elsevier B.V. All rights reserved.