Papers - Araki Kenji
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Thermal transfer simulation for concentrator photovoltaic receiver under concentration condition Reviewed
Ota Y., Nagai H., Araki K., Nishioka K.
AIP Conference Proceedings 1556 18 - 21 2013
Language：English Publishing type：Research paper (scientific journal) Publisher：AIP Conference Proceedings
© 2013 AIP Publishing. Under concentration conditions, it is important to manage the operating temperature of a concentrator photovoltaic (CPV) module, because a high-density solar energy enters into the solar cell. We measured the temperature of the CPV module. In the outdoor operation, the module back surface temperature of the CPV module was 3.3 K lower than the aluminum stage temperature. Moreover, we developed a thermal transfer model for the CPV module and calculated the temperature in it using a thermal transfer simulator. The temperatures in CPV module were calculated as a function of the thermal resistance between aluminum stage and back chassis. The temperature coefficient of Voc using calculated solar cell temperature and measured Voc was approximately -0.22%, which was in good agreement with previous report. The simulation results showed that the thicker back chassis and higher heat emissivity were effective for the reduction of operating temperature of CPV module.
DOI： 10.1063/1.4822189
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Thermal transfer simulating for concentrator photovoltaic module under concentration condition Reviewed
Ota Y., Nagai H., Araki K., Nishioka K.
Conference Record of the IEEE Photovoltaic Specialists Conference 470 - 473 2013
Language：English Publishing type：Research paper (scientific journal) Publisher：Conference Record of the IEEE Photovoltaic Specialists Conference
Under concentration conditions, it is important to manage the operating temperature of a concentrator photovoltaic (CPV) module, because a high-density solar energy enters into the solar cell. We measured the temperature of the CPV module. In outdoor operation, the back surface temperature of the CPV module was 6.2 K lower than aluminum stage temperature. Moreover, we developed a thermal transfer model for the CPV module and calculated the temperature in CPV module as functions of the thermal resistance and the heat transfer coefficient using a thermal transfer simulator. The simulation results showed that the lower thermal resistance between the solar cell and the back surface and higher heat transfer coefficient of back surface were effective for the reduction of operating temperature. The estimated heat transfer coefficient was comparatively near with the theoretical value. By using the developed model, we can estimate the operating temperature in concentrating operation. © 2013 IEEE.
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Al Husna H., Shibata N., Sawano N., Ueno S., Ota Y., Minemoto T., Araki K., Nishioka K.
AIP Conference Proceedings 1556 252 - 255 2013
Language：English Publishing type：Research paper (scientific journal) Publisher：AIP Conference Proceedings
© 2013 AIP Publishing. Multi-junction solar cell is designed to have considerable effect towards the solar spectrum distribution so that the maximum solar radiation could be absorbed hence, enhancing the energy conversion efficiency of the cell. Due to its application in CPV system, the system's characteristics are more sensitive to environmental factor in comparison to flat-plate PV system which commonly equipped with Si-based solar cell. In this paper, the impact of environmental factors i.e. average photon energy (APE) and temperature of solar cell (Tcell) towards the performance of the tracking type CPV system were discussed. A year data period of direct spectral irradiance, cell temperature, and power output which recorded from November 2010 to October 2011 at a CPV system power generator plant located at Miyazaki, Japan was used in this study. The result showed that most frequent condition during operation was at APE = 1.87±0.005eV, Tcell = 65±2.5°C with performance ratio of 83.9%. Furthermore, an equivalent circuit simulation of a CPV subsystem in module unit was conducted in order to investigate the influence of environmental factors towards the performance of the module.
DOI： 10.1063/1.4822243
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Espinet-González P., Algora C., Núñez N., Orlando V., Vázquez M., Bautista J., Araki K.
AIP Conference Proceedings 1556 222 - 225 2013
Language：English Publishing type：Research paper (scientific journal) Publisher：AIP Conference Proceedings
© 2013 AIP Publishing. A temperature accelerated life test on commercial concentrator lattice-matched GaInP/GaInAs/Ge triplejunction solar cells has been carried out. The solar cells have been tested at three different temperatures: 119, 126 and 164 °C and the nominal photo-current condition (820 X) has been emulated by injecting current in darkness. All the solar cells have presented catastrophic failures. The failure distributions at the three tested temperatures have been fitted to an Arrhenius-Weibull model. An Arrhenius activation energy of 1.58 eV was determined from the fit. The main reliability functions and parameters (reliability function, instantaneous failure rate, mean time to failure, warranty time) of these solar cells at the nominal working temperature (80 °C) have been obtained. The warranty time obtained for a failure population of 5 % has been 69 years. Thus, a long-term warranty could be offered for these particular solar cells working at 820 X, 8 hours per day at 80 °C.
DOI： 10.1063/1.4822236
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Durability of polymeric encapsulation materials in a PMMA/glass concentrating photovoltaic system Reviewed
Miller D.C., Kempe M.D., Muller M.T., Kennedy C.E., Araki K., Kurtz S.R.
Optics InfoBase Conference Papers 2013
Language：English Publishing type：Research paper (scientific journal) Publisher：Optics InfoBase Conference Papers
Many CPV cells are coupled to an optical component/coverglass with a polymer. We describe a screen test to identify field-induced failure modes in popular encapsulation materials. Results are presented for 36 months cumulative exposure. Renewable Energy and the Environment Congress. © 2013.
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Detailed effects of wind on the field performance of a 50 kW CPV demonstration plant Reviewed
Castro M., Domínguez C., Núñez R., Antón I., Sala G., Araki K.
AIP Conference Proceedings 1556 256 - 260 2013
Language：English Publishing type：Research paper (scientific journal) Publisher：AIP Conference Proceedings
© 2013 AIP Publishing. The effect of the wind speed and direction on the arrays in a 50 kW plant was analyzed along several days. The wind is measured in different positions of the plant: the general plant meteorological station, the module's boundary layer and the close surroundings of the array. The averaged thermal resistance between the back of the module and the ambient is calculated and its dependence with the wind direction analyzed. Early results suggest that Northern wind has a better cooling effect than Western and Eastern winds.
DOI： 10.1063/1.4822244
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Two interactive and practical methods for optimization of tracker allocation in a given land Reviewed
Araki K.
AIP Conference Proceedings 1477 244 - 247 2012.12
Language：English Publishing type：Research paper (scientific journal) Publisher：AIP Conference Proceedings
The purpose of this paper is proposals of two interactive methods of tracker allocation effective to relatively smaller installation. Interaction helps designers to consider every detail of the limitation and possibly more accurate approach to the project of narrow land space rather than blindly relying mathematical optimum calculation. One is Overlay of skewed rectangular mesh method. This is a simple implementation of classical optimization calculation to interactive environment. Another is Butterfly method. The idea of using butterfly pattern was first invented by Spanish engineer, Dobon, and often called Dobon's butterfly in European regions. The original definition is the contour plot on the influence shading from a single tracker. We have improved this method for interactive design tool. © 2012 American Institute of Physics.
DOI： 10.1063/1.4753878
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Impact of volcanic ash on CPV system in Miyazaki Japan Reviewed
Ota Y., Araki K., Nishioka K.
AIP Conference Proceedings 1477 340 - 343 2012.12
Language：English Publishing type：Research paper (scientific journal) Publisher：AIP Conference Proceedings
Recently, large-scale photovoltaic (PV) systems have attracted attention. In the field-operation, the electric power generations of PV systems, including CPV system, are affected by the natural environment such as ambient temperature, snowfall, soiling, etc. In this study, we assessed the impact of the volcanic ash on CPV system, and the output characteristics of the CPV and CIS systems were compared. The output of CIS PV system was drastically decreased by the volcanic ash. On the other hand, in the case of the CPV system, the output was not decreased so much. © 2012 American Institute of Physics.
DOI： 10.1063/1.4753900
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The dome-shaped Fresnel-Köhler concentrator Reviewed
Zamora P., Benitez P., Li Y., Miñano J., Mendes-Lopes J., Araki K.
AIP Conference Proceedings 1477 69 - 72 2012.12
Language：English Publishing type：Research paper (scientific journal) Publisher：AIP Conference Proceedings
Manufacturing tolerances, along with a high concentration ratio, are key issues in order to obtain cheap CPV systems for mass production. Consequently, this manuscript presents a novel tolerant and cost effective concentrator optic: the domed-shaped Fresnel-Köhler, presenting a curved Fresnel lens as Primary Optical Element (POE). This concentrator is based on two previous successful CPV designs: the FK concentrator, based on a flat Fresnel lens, and the dome-shaped Fresnel lens system developed by Daido Steel, resulting on a superior concentrator. The manuscript shows outstanding simulation results for geometrical concentration factor of Cg=1,230x: high tolerance and high optical efficiency, achieving acceptance angles of 1.18° (dealing to a CAP*=0.72) and efficiencies over 85% (without any anti-reflective coating). Moreover, Köhler integration provides good irradiance uniformity on the cell surface without increasing system complexity by means of any extra element. Daido Steel advanced technique for demolding injected plastic pieces will allow for easy manufacture of the dome-shaped POE of DFK concentrator. © 2012 American Institute of Physics.
DOI： 10.1063/1.4753836
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Temperature distribution in 820X CPV module during outdoor operation Reviewed
Ota Y., Nagai H., Araki K., Nishioka K.
AIP Conference Proceedings 1477 364 - 367 2012.12
Language：English Publishing type：Research paper (scientific journal) Publisher：AIP Conference Proceedings
Under the concentration conditions, it is important to manage the operating temperature of CPV module, because the high density solar energy is emitted to the solar cell. The operating temperature is a dominant factor for CPV module efficiency. We analyzed the temperature distribution in a 820X module modified to measure the temperature and output of each receiver. The relationship between the operating temperature and the module efficiency was clarified. © 2012 American Institute of Physics.
DOI： 10.1063/1.4753906
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Proposal of an energy rating method fair to countries of lower irradiance resources Reviewed
Araki K.
AIP Conference Proceedings 1477 344 - 347 2012.12
Language：English Publishing type：Research paper (scientific journal) Publisher：AIP Conference Proceedings
International standard must be fair among nations. Fairness means fair among manufactures, testers and users. Present typical approaches, based on linear approximation and sampling only "good climate", may be improved by assuring fairness among spectrum and irradiance conditions among nations. In unwanted area, low efficiency days are usually humid and white-sky days. The energy anticipation will be underestimated based on the measurement by manufacturers in unwanted countries. This is not fair among manufactures. If we only filter "good climate data", it may be helpful to users in good irradiance area. This filtering may be blind to the realistic conditions. This is not fair to users. The robust approach will be parabolic representation of "daily energy" based on more than 10 days data. © 2012 American Institute of Physics.
DOI： 10.1063/1.4753901
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Photovoltaic performance of the dome-shaped fresnel-köhler concentrator Reviewed
Zamora P., Benítez P., Li Y., Miñano J., Mendes-Lopes J., Araki K.
Proceedings of SPIE - The International Society for Optical Engineering 8468 2012.12
Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of SPIE - The International Society for Optical Engineering
In order to have a cost-effective CPV system, two key issues must be ensured: high concentration factor and high tolerance. The novel concentrator we are presenting, the dome-shaped Fresnel-Köhler, can widely fulfill these two and other essential issues in a CPV module. This concentrator is based on two previous successful CPV designs: the FK concentrator with a flat Fresnel lens and the dome-shaped Fresnel lens system developed by Daido Steel, resulting on a superior concentrator. The concentrator has shown outstanding simulation results, achieving an effective concentrationacceptance product (CAP) value of 0.72, and an optical efficiency of 85% on-axis (no anti-reflective coating has been used). Moreover, Köhler integration provides good irradiance uniformity on the cell surface and low spectral aberration of this irradiance. This ensures an optimal performance of the solar cell, maximizing its efficiency. Besides, the domeshaped FK shows optimal results for very compact designs, especially in the f/0.7-1.0 range. The dome-shaped Fresnel- Köhler concentrator, natural and enhanced evolution of the flat FK concentrator, is a cost-effective CPV optical design, mainly due to its high tolerances. Daido Steel advanced technique for demolding injected plastic pieces will allow for easy manufacture of the dome-shaped POE of DFK concentrator. © 2012 SPIE.
DOI： 10.1117/12.929698
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Optical design of the dome-shaped fresnel-köhler concentrator Reviewed
Zamora P., Benítez P., Li Y., Miñano J., Mendes-Lopes J., Araki K.
Proceedings of SPIE - The International Society for Optical Engineering 8485 2012.12
Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of SPIE - The International Society for Optical Engineering
The dome-shaped Fresnel-Köhler concentrator is a novel nonimaging optical design for photovoltaic applications. It is based on two previous successful CPV optical designs: the FK concentrator with a flat Fresnel lens and the dome-shaped Fresnel lens system developed by Daido Steel, resulting on a superior concentrator. This optical concentrator will be able to achieve large concentration factor, high tolerance (i.e. acceptance angle) and high optical efficiency, three key issues when dealing with photovoltaic applications. Besides, its irradiance is distributed on the cell surface in a very even way. The concentrator has shown outstanding simulation results, achieving an effective concentration-acceptance product (CAP*) value of 0.72, an on-axis optical efficiency over 85% and good irradiance uniformity on the cell provided by Köhler integration. Furthermore, due to its high tolerances, we will present the dome-shaped Fresnel-Köhler concentrator as a cost-effective CPV optical design. This all makes this concentrator superior to other conventional competitors in the current market. © 2012 SPIE.
DOI： 10.1117/12.929723
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Ota Y., Sueto T., Nagai H., Araki K., Nishioka K.
Conference Record of the IEEE Photovoltaic Specialists Conference 961 - 964 2012.11
Language：English Publishing type：Research paper (scientific journal) Publisher：Conference Record of the IEEE Photovoltaic Specialists Conference
Under the concentration conditions, it is important to manage the operating temperature of CPV module, because the high density solar energy is emitted to the solar cell. The operating temperature is a dominant factor for CPV module efficiency. We analyzed the temperature distribution in a 820X module modified in order to measure the temperature and output of each receiver. As the results, the relationship between the operating temperature and the module efficiency was clarified. © 2012 IEEE.
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Nabemoto K., Sakurada Y., Ota Y., Takami K., Nagai H., Tamura K., Araki K., Nishioka K.
Japanese Journal of Applied Physics 51 ( 10 PART 2 ) 2012.10
Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics
An anti-soiling layer was coated on a poly(methyl methacrylate) (PMMA) substrate. The anti-soiling layer was prepared by coating the acrylic urethane capping layer, the inorganic/organic nano-graded intermediate layer, and the photocatalytic surface layer including modified WO 3 and partial hydrolyzed tetraethyl orthosilicate. The layers were coated by spin-coat method. The photocurrent from each subcell of the InGaP/InGaAs/ Ge triple-junction solar cell can be calculated by multiplying the solar spectrum of AM1.5D (850W/m 2), the transmittance of the PMMA substrate, and the spectral response of the triple-junction solar cell. After 8 months exposure, the reduction rate of photocurrent of the sample without antisoiling coat was 9.6%. On the other hand, that with anti-soiling coat could be suppressed to 3.3%. © 2012 The Japan Society of Applied Physics.
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Sandblasting durability of acrylic and glass Fresnel lenses for concentrator photovoltaic modules Reviewed
Nishioka K., Ikematsu K., Ota Y., Araki K.
Solar Energy 86 ( 10 ) 3021 - 3025 2012.10
Language：English Publishing type：Research paper (scientific journal) Publisher：Solar Energy
The impact of sandblasting on Fresnel lenses for concentrator photovoltaic (CPV) modules must be carefully considered when CPV systems are installed in desert areas. In this study, the transmittance after sandblasting of acrylic polymethylmethacrylate (PMMA) and glass substrates was evaluated, and their durability was assessed. The transmittance decreased as the momentum of the blown sand increased. The conversion efficiency of the CPV modules was estimated using equivalent circuit calculations, and the influence of sandblasting on the output of the CPV modules was quantitatively predicted. The coefficients of degradation for the PMMA and glass CPV modules were 0.17 and 0.08 points per unit of momentum, respectively. The durability of the CPV module with the glass Fresnel lens is approximately twice that with the PMMA lens. © 2012 Elsevier Ltd.
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Two-dimensional mapping of localized characteristics of concentrator photovoltaic module Reviewed
Yano H., Nagai H., Tamura K., Araki K., Nishioka K.
Materials Science Forum 725 187 - 190 2012
Language：English Publishing type：Research paper (scientific journal) Publisher：Materials Science Forum
For the development of concentrator photovoltaic (CPV) module realizing high efficiency, it is necessary to achieve the high efficiency optical system including Fresnel lens and homogenizer. For the improvement of optical systems, it is very important to understand the contribution of the light irradiated to a localized position on the Fresnel lens. The light beam induced current (LBIC) system was constructed to evaluate the focusing characteristic of the CPV module. We locally irradiated a light from solar simulator to the CPV mini-module and measured the generation current, and the localized characteristics were represented by two-dimensional mappings. Moreover, we evaluated the influence of tracking error by changing the irradiation angle. In the case of tracking errors, the peak of generated current was shifted and the current was decreased. In the case of tracking error of 1.0°, the total generated current was reduced 12%, in comparison with the normal irradiance. © (2012) Trans Tech Publications, Switzerland.
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Espinet-González P., Algora C., Orlando V., Núñez N., Vázquez M., Bautista J., Xiugang H., Barrutia L., Rey-Stolle I., Araki K.
Conference Record of the IEEE Photovoltaic Specialists Conference 2 2012
Language：English Publishing type：Research paper (scientific journal) Publisher：Conference Record of the IEEE Photovoltaic Specialists Conference
A quantitative temperature accelerated life test on sixty GaInP/GaInAs/Ge triple-junction commercial concentrator solar cells is being carried out. The final objective of this experiment is to evaluate the reliability, warranty period, and failure mechanism of high concentration solar cells in a moderate period of time. The acceleration of the degradation is realized by subjecting the solar cells at temperatures markedly higher than the nominal working temperature under a concentrator, while the photo-current nominal conditions are emulated by injecting current in darkness. Three experiments at three different temperatures are necessary in order to obtain the acceleration factor which relates the time at the stress level with the time at nominal working conditions. However, up to now only the test at the highest temperature has finished. Therefore, we can not provide complete reliability information but we have analyzed the life data and the failure mode of the solar cells inside the climatic chamber at the highest temperature. The failures have been all of them catastrophic. In fact, the solar cells have turned into short circuits. We have fitted the failure distribution to a two parameters Weibull function. The failures are wear-out type. We have observed that the busbar and the surrounding fingers are completely deteriorated.
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Araki K., Al Taher O., Nagai H., Hebert P., Valles J.
AIP Conference Proceedings 1407 303 - 306 2011.12
Language：English Publishing type：Research paper (scientific journal) Publisher：AIP Conference Proceedings
Two types of failure of III-V cells in CPV system by Daido Steel have been observed. One is thermal runaway and another is what we call a electrical shock. This paper will discuss on the frequency of the cell failure seen in a field and on experiments to determine the root cause of thermal runaway. Failures by the electrical shock were not related to thermal runaway, and a packaging solution to the failure by the electrical shock was found which will be published at another time. A detailed investigation of 30 kW field was undertaken to identify failed cells. After the other failure mechanism has been removed, experiments can be conducted on thermal runaway. Thermal runaway can occur due to loss of thermal conduction, such as voids or discontinuities in the thermal interchange material bonding cell to heat sink. It has been hypothesized that thermal runaway can also occur at location of cell defects as identified by electroluminescence. So far it we have not been able to induce thermal runaway at locations of electroluminescence defects. © 2011 American Institute of Physics.
DOI： 10.1063/1.3658349
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Output comparison of CPV and flat-plate systems in Japanese meteorological condition Reviewed
Shibata N., Ota Y., Sakurada Y., Takahashi Y., Kumagai I., Araki K., Nishioka K.
AIP Conference Proceedings 1407 341 - 344 2011.12
Language：English Publishing type：Research paper (scientific journal) Publisher：AIP Conference Proceedings
The output characteristics of tracking type concentrator photovoltaic (CPV), tracking type silicon solar cell, and fixed silicon solar cell were compared in Japanese meteorological condition. At first, the module characteristics were evaluated. In the noon, output power of the CPV module was twice the crystalline silicon modules. In the morning and evening, tracked modules generated higher power due to the tracking. Next, the characteristics of 14 kW CPV system and 50 kW multi-crystalline silicon PV system were evaluated and compared. The output of CPV system was high but unstable because the CPV system was susceptible to meteorological conditions. The CPV system runs ahead of the crystalline silicon PV system under the conditions that the global irradiance per a day is more than 5kWh/m2 and the direct normal irradiance per a day is more than 4kWh/m2. © 2011 American Institute of Physics.
DOI： 10.1063/1.3658357