Papers - Araki Kenji
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Super high-efficiency multi-junction and concentrator solar cells Reviewed
Yamaguchi M., Takamoto T., Araki K.
Solar Energy Materials and Solar Cells 90 ( 18-19 ) 3068 - 3077 2006.11
Language：English Publishing type：Research paper (scientific journal) Publisher：Solar Energy Materials and Solar Cells
III-V compound multi-junction (MJ) (tandem) solar cells have the potential for achieving high conversion efficiencies of over 50% and are promising for space and terrestrial applications. We have proposed AlInP-InGaP double hetero (DH) structure top cell, wide-band gap InGaP DH structure tunnel junction for sub cell interconnection, and lattice-matched InGaAs middle cell. In 2004, we have successfully fabricated world-record efficiency concentrator InGaP/InGaAs/Ge 3-junction solar cells with an efficiency of 37.4% at 200-suns AM1.5 as a result of widening top cell band gap, current matching of sub cells, precise lattice matching of sub cell materials, proposal of InGaP-Ge heteroface bottom cell, and introduction of DH-structure tunnel junction. In addition, we have realized high-efficiency concentrator InGaP/InGaAs/Ge 3-junction solar cell modules (with area of 7000 cm2) with an out-door efficiency of 27% as a result of developing high-efficiency InGaP/InGaAs/Ge 3-junction cells, low optical loss Fresnel lens and homogenizers, and designing low thermal conductivity modules. Future prospects are also presented. We have proposed concentrator III-V compound MJ solar cells as the 3rd-generation solar cells in addition to 1st-generation crystalline Si solar cells and 2nd-generation thin-film solar cells. We are now challenging to develop low-cost and high output power concentrator MJ solar cell modules with an output power of 400 W/m2 for terrestrial applications and high-efficiency, light-weight and low-cost MJ solar cells for space applications. © 2006 Elsevier B.V. All rights reserved.
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Development of Low-Concentration Linear-Array Photovoltaic System with Two-Axes Tracking Reviewed
ICHIKAWA Naoki, OKE Shinichiro, KEMMOKU Yoshishige, TAKIKAWA Hirofumi, SAKAKIBARA Tateki, ARAKI Kenji
2006 257 - 260 2006.10
Language：English Publishing type：Research paper (scientific journal)
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A small sun in an ETUI -Possibilities in HCPV- Reviewed
Araki K., Hiramatsu M., Kemmoku Y., Akisawa A., Yamaguchi M.
Conference Record of the 2006 IEEE 4th World Conference on Photovoltaic Energy Conversion, WCPEC-4 1 603 - 608 2006
Language：English Publishing type：Research paper (scientific journal) Publisher：Conference Record of the 2006 IEEE 4th World Conference on Photovoltaic Energy Conversion, WCPEC-4
This paper discusses on possibilities of HCPV, including (1) cost (2) reliability (3) performance and (4) applications. The reduction of the cost is achieved by the reduction of the material itself. The material is not special. HCPV does not covered by special materials including pure Si, TCO, Ru-based dye, or Pt electrode or other materials using CVD or other vacuum process. HCPV modules are made without special tools. Local assembly is also possible. The weight of the 300 W HCPV module Is 22 kg corresponding 0.07 kg/W. It is about 70 % of the MC-Si flatplate modules and less than half of the high efficiency tandem thin film modules. The recent 1-year field test done in Japan showed that the HCPV generated 1.6 times energy per area than that of the crystalline Si module (fixed installation). This implies that the HCPV has an advantage not only desert area but wet and cloudy area. Intensive reliability tests were done to the HCPV module. One of the keys are lifetime of the receiver against 20 years of accumulated CONCENTRATED UV flux in wet environment and other accelerated environment. Finally, the new applications of HCPV including rooftop installation and see-through design are discussed. © 2006 IEEE.
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High efficiency concentrator multi-junction solar cells and modules Reviewed
Yamaguchi M., Takamoto T., Araki K.
Proceedings of the Solar World Congress 2005: Bringing Water to the World, Including Proceedings of 34th ASES Annual Conference and Proceedings of 30th National Passive Solar Conference 2 998 - 1003 2005.12
Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of the Solar World Congress 2005: Bringing Water to the World, Including Proceedings of 34th ASES Annual Conference and Proceedings of 30th National Passive Solar Conference
This paper reviews Japanese research and development (R&D) activities of III-V compound multi-junction (MJ) solar cells, concentrator MJ solar cells and modules. Potential of high-efficiency and low-cost using concentrator MJ solar cell modules is shown. 39.2% efficiency at 200- suns AM1.5G has been realized with InGaP/InGaAs/Ge 3- junction solar cells at Sharp Co. The peak efficiency for a 7,056 cm2 400 X module with 36 solar cells connected in series was 26.6 % (measured in house). The peak efficiencies (around 27.5%) of the same type of the modules with 6 solar cells connected in series and 1,176 cm2 area were confirmed by measurements at the Frunhofer ISE, NREL and Toyohashi University of Technology. Future prospects will also be presented.
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Comparison of efficiency measurements for a HCPV module with 3J cells in 3 sites Reviewed
Araki K., Emery K., Siefer G., Bett A.W., Sakakibara T., Kemmoku Y., Ekins-Daukes N.J., Lee H.S., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 846 - 849 2005.11
Language：English Publishing type：Research paper (scientific journal) Publisher：Conference Record of the IEEE Photovoltaic Specialists Conference
A new HCPV with 3J solar cells and new concentrator optics consisting in a dome-shaped Fresnel lens and a kaleidoscope homogenizer was presented in the last SCC2003. This paper summarizes the evaluation done by three independent organizations and a manufacturer. The peak uncorrected efficiency for a 7,056 cm2 400 X (Geometrical concentration ratio) module with 36 solar cells connected in series was 26.6 % was measured in house. The peak uncorrected efficiencies of the same type of the module with 6 solar cells connected in series and 1,176 cm2 area measured by Fraunhofer ISE, NREL and Toyohashi University of Technology were 27.4 %, 24.8 % and 25.9 % respectively. The peak uncorrected efficiency for a 550X and 5,445 cm2 module with 20 solar cells connected in series was 28.9 % in house. The peak uncorrected efficiency of the 550X (Geometrical concentration ratio) module evaluated by Toyohashi University of Technology was 27.0 %. The temperature corrected efficiency under the best sunshine condition in Japan for the 550X module was 31.5 ± 1.7 %. © 2005 IEEE.
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Syracuse - A multi-junction concentrator system computer model Reviewed
Ekins-Daukes N.J., Betts T.R., Kemmoku Y., Araki K., Lee H.S., Gottschalg R., Boreland M.B., Infield D.G., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 651 - 654 2005.11
Language：English Publishing type：Research paper (scientific journal) Publisher：Conference Record of the IEEE Photovoltaic Specialists Conference
A multi-junction concentrator system computer model is presented, that aims to accurately model the power generated based on environmental data input, such as the irradiance, air temperature, humidity and pressure. The device model is discussed, illustrating the importance of statistical variation of module components when simulating a multi-cell module. This comprehensive concentrator computer model will be released for general use, aiming to become a useful resource for those designing and testing multi-junction based concentrator systems. ©2005 IEEE.
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Lee H.S., Ekins-Daukes N.J., Araki K., Kemmoku Y., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 754 - 757 2005.11
Language：English Publishing type：Research paper (scientific journal) Publisher：Conference Record of the IEEE Photovoltaic Specialists Conference
The behavior of triple junction concentrator cell (InGaP/(In)GaAs/Ge) under the control of cell temperature is investigated and evaluated at Toyota Technological Institute of Japan. The aim of this study is to investigate an accurate temperature coefficient as comparing the outdoor test with the theoretical calculation as a function of a sunlight concentration. Recently, the field test consisted of a total of 6 modules at two sites (Inuyama, Toyohashi) of Japan shows the peak efficiency of 26.8%±1.5%, and the triple junction cell shows the efficiency of 38.9% at 489suns. In this study, a new dome-typed Fresnel lens (550X) that has the optical efficiency of 85.8% was used. The homogenizer is placed on the holder designed to control the cell temperature, and the outdoor test using the solar tracker was carried out under the 400X, 550X lenses. The conversion efficiency increases with the direct solar radiation, and decreases as increasing the receiver temperature. However, no change in Isc was observed, and Voc decreased slightly as a function of the receiver temperatures. The temperature coefficient obtained from the receiver at TTI shows the similar trends with them from the bare cell at Nara-AIST. © 2005 IEEE.
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FUKUSHIGE Naoyuki, MATSUZAKI Yozo, OKE Shinichiro, KEMMOKU Yoshishige, TAKIKAWA Hirofumi, SAKAKIBARA Tateki, ARAKI Kenji
2005 291 - 294 2005.10
Language：English Publishing type：Research paper (scientific journal)
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Influence of Spectrum Intensity of Each Wavelength Range on Output of Si Photodiode Pyrheliometer Reviewed
MATSUZAKI Yozo, FUKUSHIGE Naoyuki, OKE Shinichiro, KEMMOKU Yoshishige, TAKIKAWA Hirofumi, SAKAKIBARA Tateki, ARAKI Kenji
2005 185 - 188 2005.10
Language：English Publishing type：Research paper (scientific journal)
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Multi-junction III-V solar cells: Current status and future potential Reviewed
Yamaguchi M., Takamoto T., Araki K., Ekins-Daukes N.
Solar Energy 79 ( 1 ) 78 - 85 2005.7
Language：English Publishing type：Research paper (scientific journal) Publisher：Solar Energy
Our recent R&D activities of III-V compound multi-junction (MJ) solar cells are presented. Conversion efficiency of InGaP/InGaAs/Ge has been improved up to 31-32% (AM1.5) as a result of technologies development such as double hetero-wide band-gap tunnel junction, InGaP-Ge hetero-face structure bottom cell, and precise lattice-matching of InGaAs middle cell to Ge substrate by adding indium into the conventional GaAs layer. For concentrator applications, grid structure has been designed in order to reduce the energy loss due to series resistance, and world-record efficiency InGaP/InGaAs/Ge 3-junction concentrator solar cell with an efficiency of 37.4% (AM1.5G, 200-suns) has been fabricated. In addition, we have also demonstrated high-efficiency and large-area (7000 cm2) concentrator InGaP/InGaAs/Ge 3-junction solar cell modules of an outdoor efficiency of 27% as a result of developing high-efficiency InGaP/InGaAs/Ge 3-junction cells, low optical loss Fresnel lens and homogenizers, and designing high thermal conductivity modules. Future prospects are also presented. We have proposed concentrator III-V compound MJ solar cells as the 3rd generation solar cells in addition to 1st generation crystalline Si solar cells and 2nd generation thin-film solar cells. We are now developing low-cost and high output power concentrator MJ solar cell modules with an output power of 400 W/m2 for terrestrial applications. © 2004 Elsevier Ltd. All rights reserved.
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Generated Energy of a 500X Concentrator PV System with Dome Fresnel Lens in Summer Season Reviewed
KEMMOKU Yoshishige, EGAMI Toshio, MIYAZAKI Yoshinori, HIRAMATSU Masao, ARAKI Kenji, SAKAKIBARA Tateki
Proceedings of JSES/JWEA Joint Conference 2004 173 - 176 2004.11
Language：English Publishing type：Research paper (scientific journal)
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Measurement of Dynamic Spectrum Distribution of Direct Insolation Reviewed
FUKUSHIGE Naoyuki, MATSUZAKI Yozo, OKE Shinichiro, KEMMOKU Yoshishige, TAKIKAWA Hirofumi, SAKAKIBARA Tateki, ARAKI Kenji
Proceedings of JSES/JWEA Joint Conference 2004 25 - 28 2004.11
Language：English Publishing type：Research paper (scientific journal)
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Japanese programs on novel concepts in PV Reviewed
Yamaguchi M., Takamoto T., Araki K., Imaizumi M.
Semiconductors 38 ( 8 ) 956 - 961 2004.8
Language：English Publishing type：Research paper (scientific journal) Publisher：Semiconductors
Japanese R&D activities in photovoltaics (PV) and our R&D activities with III-V compound multijunctipn (MJ) solar cells are presented. We have realized high-efficiency InGaP/InGaAs triple-junction solar cells with an efficiency of 36.5-37% (AM1.5G, 200 suns) and concentrator triple-junction solar cell modules with an outdoor efficiency of 27% as a result of designing a grid structure, developing low optical loss Fresnel lens and homgenizers, and designing low thermal conductivity modules. Our challenge now is to develop low-cost and high output power concentrator MJ solar cell modules with an output power of 400 W/m2 for terrestrial applications. © 2004 MAIK "Nauka/Interperiodica".
DOI： 10.1134/1.1787119
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Analysis on Efficiency Limit of Terrestrial Photovoltaic Reviewed
Araki Kenji, N. D. Ekins-Daukes, Yamaguchi Masafumi
DENKI-SEIKO 75 ( 3 ) 155 - 163 2004
Language：English Publishing type：Research paper (scientific journal) Publisher：Daido Steel Co., Ltd.
Monolithic multi-junction solar cells are constrained in that the current output of the stack is limited to the current being generated in the worst performing cell. This becomes a problem when the spectral content of the radiation incident on the solar cell is different to the 'designed' spectrum. The terrestrial spectrum always changes by different sun height or air mass as well as fluctuation of aerosol density. The annual power generation is expected to be smaller than the designed one, due to the spectrum mismatching. This influence may be emphasized by the increase of the number of junctions, while the efficiency under the designed standard spectrum will be increased with the number of junctions. The annual efficiency of monolithic multi-junction solar cells of more than three junctions were calculated and compared. No distinct advantage with more than 5 junctions in view of annual and daily power generation. The practical efficiency limit in real terrestrial sunshine is a little above 50 %.
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Development of 28 percent Efficient Solar Electric Concentrators Reviewed
Araki Kenji, Kondo Michio, Uozumi Hisafumi, Takamoto Tatsuya, Egami Toshio, Hiramatsu Masao, Miyazaki Yoshinori, Kemmoku Yoshishige, Yamaguchi Masafumi
DENKI-SEIKO 75 ( 3 ) 165 - 172 2004
Language：English Publishing type：Research paper (scientific journal) Publisher：Daido Steel Co., Ltd.
A 400 X and 7056 cm<sup>2</sup> concentrator module was fabricated from 36 concentrator receivers, connected in series and with the same number of newly developed dome-shape Fresnel lenses. The averaged outdoor efficiency on a clear sky day was 26.8 ±1.5 % (25C STC). This is the highest module efficiency achieved to date using a module of practical size and electrical rating. The heat was dissipated by the module wall and neither heat sinks nor external cooling were used. A glass homogenizer was introduced to give uniform illumination to the square cell, and afforded a reasonable assembly tolerance, without the need for optical alignment.
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Which is the best number of junctions for solar cells under ever-changing terrestrial spectrum? Reviewed
Araki K., Yamaguchi M., Kondo M., Uozumi H.
Proceedings of the 3rd World Conference on Photovoltaic Energy Conversion A 307 - 312 2003.12
Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of the 3rd World Conference on Photovoltaic Energy Conversion
Monolithic multi-junction solar cells are constrained in that the current output of the stack is limited to the current being generated in the worst performing cell. This becomes a problem when the spectral content of the radiation incident on the solar cell is different to the 'designed' spectrum, The terrestrial spectrum always changes by different sun height or air mass as well as fluctuation of aerosol density. The annual power generation is expected to be smaller than the designed one, due to the spectrum mismatching. This influence may be emphasized by the increase of the number of junctions, while the efficiency under the designed standard spectrum will be increased with the number of junctions. The annual efficiency of monolithic multi-junction solar cells of more than three junctions were calculated and compared. No distinct advantage with more than 5 junctions in view of annual and daily power generation. The practical efficiency limit in real terrestrial sunshine is a little above 50%.
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Development of a robust and high efficiency concentrator receiver Reviewed
Araki K., Kondo M., Uozumi H., Yamaguchi M.
Proceedings of the 3rd World Conference on Photovoltaic Energy Conversion A 630 - 633 2003.12
Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of the 3rd World Conference on Photovoltaic Energy Conversion
One of the difficulties in development of concentrator receiver using III-V solar cells is realization of robust structure with capable of high current density. Most of the cases, the top electrodes were cabled by wire bonding, conductive epoxy and silver ribbon blazing, which gradually increases series resistance under severe environment and loses reliability. Extending the MJ cell performance envelope to the economically required higher current levels and higher current density levels has involved serious and unexpected challenges. A new and robust concentrator receiver was developed with capable of more than 500 X of concentration. A 6300 cm2 and 400X concentrator module were fabricated with the new receivers. The average efficiency in clear day was 21.7 %.
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Study of the space factor for spectrum-sensitive MJ solar cell arrays Reviewed
Araki K., Kemmoku Y., Yamaguchi M.
Proceedings of the 3rd World Conference on Photovoltaic Energy Conversion C 2350 - 2353 2003.12
Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of the 3rd World Conference on Photovoltaic Energy Conversion
This is the first study of the influence of the annual power generation of PV array considering the optimum space factor. Supposing DNI (Direct Normal Irradiance) spectrum is calculated by the most recent reduced aerosol optical density model, and 3J concentrator solar cell is completely matched to air mass 1.5 calculated from that reduced-AOD or other models, the power loss factor in arbitrary months and hour angle would be calculated. The model was proved by actual observation of PV output under both concentration and non-concentration operation. It was thought that the optimum space factor in 3J concentrator solar cell was more packed than single junction cells such as crystalline silicon solar cells. It was also thought that the area efficiency in 3J solar cells was greater than the single junction cells. These were because that shadow loss in 3J solar cells appeared in low sun height was relatively less impact to the annual power generation.
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Araki K., Kondo M., Uozumi H., Yamaguchi M.
Proceedings of the 3rd World Conference on Photovoltaic Energy Conversion A 853 - 856 2003.12
Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of the 3rd World Conference on Photovoltaic Energy Conversion
This study presents the success of proving significant improvement of PV output by kaleidoscope homogenizers and their robust operation to various kinds of concentrator optics. It was also supported by theoretical calculation.
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KEMMOKU Yoshishige, MIYAKAWA Masayuki, EGAMI Toshio, ARAKI Kenji, SAKAKIBARA Tateki
2003 201 - 204 2003.11
Language：English Publishing type：Research paper (scientific journal)