Papers - NISHIOKA Kensuke
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A new solar to hydrogen conversion system with high efficiency and flexibility Reviewed
Yamashita D., Nakao H., Yonezawa Y., Nakashima Y., Ota Y., Nishioka K., Sugiyama M.
2017 6th International Conference on Renewable Energy Research and Applications, ICRERA 2017 441 - 446 2017.12
Language：English Publishing type：Research paper (international conference proceedings)
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Estimation of conversion efficiency for partially static concentrator with III-V on Si solar cell Reviewed
Ota Y., Araki K., Lee K., Yamaguchi M., Nishioka K.
AIP Conference Proceedings 1881 020010-1 - 020010-5 2017.9
Language：English Publishing type：Research paper (international conference proceedings)
DOI： 10.1063/1.5001409
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Quantifying the potential of III-V/Si partial concentrator by a statistical approach Reviewed
Lee K., Araki K., Ota Y., Nishioka K., Yamaguchi M.
AIP Conference Proceedings 1881 2017.9
Language：English Publishing type：Research paper (international conference proceedings) Publisher：AIP Conference Proceedings
© 2017 Author(s). We propose a theoretical framework for analyzing the energy yields of partial concentrators. A partial concentrator uses a concentrator cell to absorb the principal defracted or reflected light rays from its concentrator optics and a backplane cell to absorbs the diffused or defocused light. This concept can be applied to the concentrator system when accurate sun-tracking is not available, such as on a vehicle. This analysis framework provides a simplified way to describe the uncertainties of solar incidences dealt by partial concentrator. This help identified a clearer design criteria of partial concentrator in order to outperform the flat-panel PV or conventional CPV.
DOI： 10.1063/1.5001445
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Outdoor validation of the 30 minutes intermittent tracking of 100 x CPV Reviewed
Araki K., Ota Y., Lee K., Nishioka K., Yamaguchi M.
AIP Conference Proceedings 1881 2017.9
Language：English Publishing type：Research paper (international conference proceedings) Publisher：AIP Conference Proceedings
© 2017 Author(s). HCPV uses trackers, but their cost and reliability have raised problems. These problems may be solved by substantially increasing acceptance angle and mechanical tolerance. For a demonstration of the possibility of such substantial improvement, a 30 minutes intermittent tracking in high concentration applications was examined. To allow for 30 minutes intermittent tracking, both advanced optics and an advanced tracking control were investigated. For advanced optics, a 100 x refractive and dielectric concentrator was designed. It had about plus or minus 5°of acceptance angle. For advanced tracking control, a feed-forward control with a linear error correction was investigated. With combining both optimizations, it was shown that 30 minutes intermittent tracking was validated in outdoor experiments even for an as high as 100 x concentration.
DOI： 10.1063/1.5001401
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Optical and thermal simulation for wide acceptance angle CPV module Reviewed
Ahmad N., Ota Y., Araki K., Lee K., Yamaguchi M., Nishioka K.
AIP Conference Proceedings 1881 2017.9
Language：English Publishing type：Research paper (international conference proceedings) Publisher：AIP Conference Proceedings
© 2017 Author(s). Concentrator photovoltaic (CPV) technology has the potential to decrease the cost of systems in the near future by using less expensive optical elements in the system which replace the receiving surface aperture and concentrate the sunlight onto small solar cells. One of the main concerns of CPV is the need for high precision tracking system and the relation to the acceptance angle. In this paper, we proposed a CPV module with concentration ratio larger than 100 times and wide acceptance angle. An optical simulation for the module with S-TIM2 glass as a lens material was conducted to estimate the optical performance of the module. Thermal and electrical simulation was also conducted using COMSOL Multiphysics and SPICE respectively to evaluate the working temperature and electrical characteristics of the multijunction solar cell under concentration conditions.
DOI： 10.1063/1.5001400
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Is it CPV? Yes, but it is a partial CPV Reviewed
Araki K., Ota Y., Lee K., Nishioka K., Yamaguchi M.
AIP Conference Proceedings 1881 2017.9
Language：English Publishing type：Research paper (international conference proceedings) Publisher：AIP Conference Proceedings
© 2017 Author(s). III-V on Si cell is one of the most promising candidates of the low-cost and high-efficiency solar cell beyond the limit of Si cells. However, it is likely that the cost of III-V cell will keep greater than that of Si cells. The partial concentrator technology was invented to concentrate the sunlight onto smaller III-V cells on the Si cell with the increased acceptance angle for static concentrator operation. The partial concentrator allows on-axis optical loss but expands the apparent acceptance angle often beyond the thermodynamic limit. The spilled light will be saved and collected by the bottom Si cell. It is not just placing the Si cell around the concentrated III-V cell, but its design philosophy is "partially" collecting the sunlight to the III-V cell to expand the acceptance. Depending on the values of cost parameters, the cost of the partial CPV module becomes minimum at 4 x - 10 x of concentration onto the top III-V cell, meaning that the area of expensive III-V cell can be saved to 1/4 - 1/10. In the partial concentrator. There may be a better optics than the ideal concentrator. The partial concentrator can be applied not only to III-V on Si cells but also III-V "by" Si cells. This lateral configuration does not have as excellent efficiency as the III-V on Si cell, but the usage of III-V cell is only several percents of the Si cell and has good similarity on the conventional Si flat-plate module technology.
DOI： 10.1063/1.5001439
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Design of the partial concentrator lens for III-V on Si static concentration Reviewed
Araki K., Ota Y., Lee K., Nishioka K., Yamaguchi M.
AIP Conference Proceedings 1881 2017.9
Language：English Publishing type：Research paper (international conference proceedings) Publisher：AIP Conference Proceedings
© 2017 Author(s). To compete with the flat-plate crystalline Silicon cell module, III-V on Si structure is developed. However, it is clear that the situation of the higher cost of III-V cell relative to the Silicon cell will be unchanged. Then, it is preferred concentrating III-V cell for further savings. The partial concentrator is expanding the acceptance angle despite the higher concentration ratio. It is achieved by better performance balance of on-axis and high incidence angle. The new and generalized design method of the partial concentrator was developed. The profile function was constructed by selected Zernike's polynomial considering rotational symmetry. The full conditions of the calculation including the initial value and the radial and azimuthal degree of the function were examined. It was found that the recommended radial and azimuthal degree were 12 and 12.
DOI： 10.1063/1.5001412
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Ahmad N., Ota Y., Araki K., Lee K., Yamaguchi M., Nishioka K.
Japanese Journal of Applied Physics 56 ( 9 ) 092301-1 - 092301-8 2017.8
Language：English Publishing type：Research paper (scientific journal) Publisher：Institute of Physics
In this study, we propose a new concentrator photovoltaic (CPV) system design with a large-acceptance-angle lens, which tracks the sun on the basis of a new 30-min intermittent tracking method that does not require a special high-precision CPV tracking system. This will reduce costs, because a large percentage of the cost of a typical CPV system comes from the expensive accurate tracking system. The present system had a concentration ratio of 111 and an acceptance angle of 4.5°. We conducted an experiment to evaluate the thermal and electrical performances of the system in an outdoor test site in Miyazaki, Japan. The experimental results were compared with optical, thermal, and electrical simulation results. The simulated results showed good agreement with the experimental ones.
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Yoshino K., Tominaga H., Ide A., Nishioka K., Naka T.
Physica Status Solidi (C) Current Topics in Solid State Physics 14 ( 6 ) 16001777 2017.6
Language：English Publishing type：Research paper (scientific journal) Publisher：Physica Status Solidi (C) Current Topics in Solid State Physics
© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Polycrystalline a-axis oriented Ga-doped ZnO thin film could be grown on glass substrate by a conventional atmospheric spray pyrolysis at 150 °C using diethylzinc-based solution. The n-type Ga-doped ZnO thin film had a resistivity of 1.5 × 10 −3 Ω cm, a carrier concentration of 2.0 × 10 20 cm −3 and a mobility of 20.0 cm 2 (Vs) −1 at an optimal Ga content of 2 wt.% upon hydrogen annealing at 450 °C. It was assumed that an increase of the n-type carrier concentration is due to increase oxygen vacancies by reacting hydrogen and oxygen in ZnO from X-ray photoelectron spectroscopy.
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Ikari T., Ohori D., Higo A., Thomas C., Samukawa S., Nishioka K., Fukuyama A.
Nanotechnology Materials and Devices Conference, NMDC 2016 - Conference Proceedings 2016.12
Language：English Publishing type：Research paper (international conference proceedings) Publisher：Nanotechnology Materials and Devices Conference, NMDC 2016 - Conference Proceedings
© 2016 IEEE. This New top-down fabrication process using bio-template and neutral beam etching process have succeeded to grow GaAs quantum nano disc (ND) for optical communication devices. The size, the alignment and the density of ND were well controlled. Low temperature photoluminescence measurement confirmed that the quantum energy levels were formed in the present structure and made clear the usefulness of the top-down process toward a defect-free ND fabrication. Strong luminescence was observed even in an as-etched samples.
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Optimization of static concentrator photovoltaics with aspherical lens for automobile
Ota Y., Nishioka K., Araki K., Ikeda K., Lee K., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 2016-November 570 - 573 2016.11
Language：English Publishing type：Research paper (international conference proceedings) Publisher：Conference Record of the IEEE Photovoltaic Specialists Conference
© 2016 IEEE. In this paper, we optimized the basic aspherical lens for automobile using optical method. Since the panel is installed in horizontal, the distribution of incident angle that is important to concentrator optics design needs to be newly defined. By optimization of lens structure, the optical efficiency increased to 46.7%.
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Possibility of CPV for automobile energy source
Araki K., Ota Y., Ikeda K., Lee K., Nishioka K., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 2016-November 554 - 559 2016.11
Language：English Publishing type：Research paper (international conference proceedings) Publisher：Conference Record of the IEEE Photovoltaic Specialists Conference
© 2016 IEEE. Greenhouse gas emission from automobiles cannot be eliminated before having them run by the sun. Toyota Tec. Inst. is serious to develop CPV applications to automobile. One is an innovative static concentrator that selectively collects sunlight from shallow angle. Another is a solar powered EV charging station with practical size and capacity.
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Ota Y., Ahmad N., Nishioka K.
Solar Energy 136 547 - 552 2016.10
Language：English Publishing type：Research paper (scientific journal) Publisher：Solar Energy
© 2016 Elsevier Ltd The amount of radiation received by the solar cells inside a photovoltaic (PV) module is lower than that arriving at the module surface, owing to reflection and soiling of the module surface. To develop high-efficiency PV systems, these effects must be addressed. In this study, a silica-based layer with anti-reflection and anti-soiling properties was coated onto the surface of a Cu(In, Ga)Se 2 PV module and the effects were assessed. The coating method was simple, allowing it to be applied to already installed PV modules. The cleaning and coating treatments were carried out on December 25, 2014, and the arrays were exposed outdoors for 7 months to investigate the effects of the treatment. The output of the array that received the coating was 3.2% greater than that of an uncoated array. It was also found that the coating reduced the reflection of the light entering from a high incident angle.
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Possibility of static low concentrator PV optimized for vehicle installation Reviewed
Araki K., Ota Y., Ikeda K., Lee K., Nishioka K., Yamaguchi M.
AIP Conference Proceedings 1766 2016.9
Language：English Publishing type：Research paper (international conference proceedings) Publisher：AIP Conference Proceedings
© 2016, American Institute of Physics Inc. All rights reserved. One of the most direct and efficient ways in eliminating greenhouse gas emission from cars is to install a PV panel on the roof. Since the area of the roof of the car is limited, high-efficiency III-V cells will be useful. Because of the space limitation, it should be high-efficiency panel. III-V cells may be a candidate, but it should be CPV for saving cost of the cell. Considering its quick movement and appearance, trackers were thought difficult to implement. Our choice was a static concentrator customized to automobile. Special static concentrator that collects sunlight from shallow incident angle was successfully developed.
DOI： 10.1063/1.4962069
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Intermittent tracking (30 minutes interval) using a wide acceptance CPV module Reviewed
Araki K., Ota Y., Lee K., Nishioka K., Yamaguchi M.
AIP Conference Proceedings 1766 2016.9
Language：English Publishing type：Research paper (international conference proceedings) Publisher：AIP Conference Proceedings
© 2016, American Institute of Physics Inc. All rights reserved. For applications of stand-alone systems including an electric vehicle (EV) power station, a tracking system with low power consumption will be demanded. One possible solution to save idling power is intermittent tracking, for example, tracking in every 30 minutes. To achieve this, a new CPV module was designed. With the combination of an advanced feed-forward tracking control, the 30 minutes of intermittent tracking may be possible by 100 x of geometrical concentration (the projected lens area by the cell aperture area with alignment margin).
DOI： 10.1063/1.4962083
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Damage repair of lens surface in CPV by silica based coating Reviewed
Kurogi S., Ota Y., Yoshino K., Nishioka K.
AIP Conference Proceedings 1766 2016.9
Language：English Publishing type：Research paper (international conference proceedings) Publisher：AIP Conference Proceedings
© 2016, American Institute of Physics Inc. All rights reserved. We tried to repair the surface of damaged poly-methyl methacrylate and glass using a simple coating and evaluated the transmittance of direct component of light. We coated a repairing material on the damaged surface of the sample. After the first sandblasting, the transmittance and the calculated conversion efficiency of CPV decreased due to the damage derived by the sandblasting. However, after the first coating, they made a recovery due to the effect of the repairing coating. In the second step (sandblasting and coating), the recovery was also observed. Instead of replacement of damaged lens or module, the coating can bring the performance back into the improved condition.
DOI： 10.1063/1.4962079
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Carbothermal reduction process of silica formed from shirasu volcanic ash using solar furnace Reviewed
Hatakeyama K., Sato K., Nishioka K.
MATEC Web of Conferences 65 2016.7
Language：English Publishing type：Research paper (international conference proceedings) Publisher：MATEC Web of Conferences
© 2016 Owned by the authors, published by EDP Sciences. Metallurgical grade silicon was formed using Shirasu volcanic ash as starting material with solar furnace. The solar furnace was composed of two parts: Fresnel lens and reacting furnace. The reacting furnace was composed of a cylindrical vacuum chamber and quartz glass plate functioning to guide the concentrated sunlight into the furnace, and was placed at the focal point of the Fresnel lens. The sample was made from a mixture of silica formed from Shirasu volcanic ash and carbon, and placed in the carbon crucible inside the reacting furnace. The sample was irradiated for 3 hours, and the furnace was left until it cooled down to room temperature. After the cooling process, the sample was mixed and placed in the carbon crucible, and it was irradiated and cooled with the same processes again. After the experiment, the sample was evaluated by X-ray diffraction and the production of silicon was confirmed.
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Ahmad N., Hatakeyama K., Ota Y., Nishioka K.
MATEC Web of Conferences 65 2016.7
Language：English Publishing type：Research paper (international conference proceedings) Publisher：MATEC Web of Conferences
© 2016 Owned by the authors, published by EDP Sciences. This paper presents a comparison of three-dimensional simulation for concentrator photovoltaic module using two types of multi-junction solar cell. Each had its own range of spectral response and based on that range a thin film filter was developed for each case to reflect the unused spectral of the solar spectrum and allowed the desired spectrum to reach the solar cell. The thin film was deposited on a secondary optical element that was used to homogenize the irradiance distribution on the solar cell. A thermal simulation was conducted to compare the resulted decrease in cell temperature due to the use of the thin film for each case.
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Reduction of temperature in silicon photovoltaic module using thermal radiation coating Reviewed
Nakamura S., Nishioka K.
MATEC Web of Conferences 65 2016.7
Language：English Publishing type：Research paper (international conference proceedings) Publisher：MATEC Web of Conferences
© 2016 Owned by the authors, published by EDP Sciences. The temperature of solar cells increases under the actual operating conditions, and the conversion efficiency of solar cells decreases with increasing temperature. In this study, a thermal radiation layer was coated on the back sheet of the PV module by a spray coating method and the effect was evaluated. The thickness of the layer was 30 μm. The temperature of the PV module with the thermal radiation coating was lower than that of the PV module without the thermal radiation coating. And the operating temperature range of the PV module with the thermal radiation coating was decreased by 2~3°C. The open-circuit voltage of the PV module with the thermal radiation coating was 0.1 V higher than that of the module without the coating due to the thermal radiation coating.
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Nakamura S., Sakamoto K., Nishioka K.
MATEC Web of Conferences 65 2016.7
Language：English Publishing type：Research paper (international conference proceedings) Publisher：MATEC Web of Conferences
© 2016 Owned by the authors, published by EDP Sciences. The temperature of solar cells considerably increases under light-concentrating operations, and the conversion efficiency of solar cells decreases with increasing temperature. It is very important to reduce the cell temperature in concentrator photovoltaic modules. The thermal radiation layers with high thermal emissivity and thermal conductivity was coated on the aluminum samples which is used for the chassis of concentrator photovoltaic and the effect was evaluated under the conditions with wind. The temperature of sample with coating showed lower temperature than that without coating. In the condition with wind, the coated sample with high thermal emissivity and high thermal conductivity showed the lowest temperature due to the effect of thermal radiation and thermal conduction.