Journal of Japan Solar Energy Society
Online ISSN : 2433-5592
Print ISSN : 0388-9564
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Research paper
  • Yugo TANAKA, Atsushi AKISAWA, Masayuki NAKAYAMA
    2020 Volume 46 Issue 3 Pages 71-76
    Published: May 31, 2020
    Released: June 06, 2020
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    This study proposes a photovoltaic(PV) module which is in the shape of triangular pyramids consisting of flat mirrors and PV cells. The mirrors provide not only solar concentration but also sun tracking function even though the module is fixed. It is expected to have the effects of increasing solar collection on to the cells and reducing installation area because the modules will be set on the ground without any space between them. The objectives of this study are to evaluate the performance of the proposed module in terms of annual solar collection and to derive appropriate design of the pyramid shape. Ray-tracing simmulation was employed to analyze the effect of the triangular pyramid design. Two kinds of index were defined, that is, solar collection per cell area and that per installation area. The results show that it is possible to find out the design cases to increase both indexes compared with a conventional PV panel setting. It is also found that there is pareto optimum set which gives the best performances with trade-off relationship between the two indexes. According to the results, the solar collection per cell area can be improved by 25% while that per installation area by 55% at the maximum. The strategies to design appropriate triangular pyramids were derived from the pareto optimum set. Another design strategy was also examined, which enhances the solar collection especially in the morning and late afternoon. Some design cases achieve the improvement in such point of view, which verifies the ability of sun tracking with fixed structure of the proposed module.

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  • Kazuto YUKITA, Katsuhiro ICHIYANAGI, Yasuyuki GOTO, Toshiro MATSUMURA, ...
    2020 Volume 46 Issue 3 Pages 77-84
    Published: May 31, 2020
    Released: June 06, 2020
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    We estimated the distant cloud cover by the all-sky image data for forecasting amount of solar energy for short periods. It is confirmed that the time variation of estimated cloud cover is leading and having similar shape to the observed solar radiation. The main result in this study is as follows. (1) According to the image processing results of the cloud, the JPEG data almost similar to RAW data. Therefore, JPEG data file is small memory capacity, high resolution and it is superior as image data collection file format. (2)The ceilometer observes the cloud cover in π/3 rad around the zenith. To the observed solar radiation, the time variation of estimated cloud cover is similar, but also lagged. (3)We presented the estimating method of distant cloud cover by using saturation level of the all-sky cloud image. To the observed solar radiation, the time variation of estimated-distant cloud cover is similar and leading for several ten minutes from several minute. (4)The data to use for an estimate of distant cloud cover is obtained by all-sky image camera with the GPS timer. Therefore, the presented method will be feasible easily.

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  • Yoshiro IZUMI, Yuzuru UEDA
    2020 Volume 46 Issue 3 Pages 85-93
    Published: May 31, 2020
    Released: June 06, 2020
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    Degradation analysis methods of PV modules using many outdoor Current-Voltage (I-V) curve data are proposed in this paper. The I-V curve data measured under various outdoor conditions are translated to the Standard Test Conditions (STC) by two kinds of translation procedures. Procedure.1 directly translates to the STC by linear interpolation method (LIM) with many reference I-V curves, which are created by I-V curve fittings. Procedure.2 is a combination of procedure1 and translation formula. Characteristic values such as maximum power, short circuit current, open circuit voltage, fill factor, series resistance and shunt resistance are quantitatively evaluated with both methods. Degradation rates of mono crystalline Si and polycrystalline Si modules were analyzed and accuracies were verified by comparing with indoor measurement results. Although open circuit voltage between the two proposed methods were different, the almost same annual degradation rates were obtained.

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  • Satoshi SAWADA, Sanshiro YAMANAKA, Yasuhiro AOYAMA, Yuki NISHIDO, Hiro ...
    2020 Volume 46 Issue 3 Pages 94-102
    Published: May 31, 2020
    Released: June 06, 2020
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    Potential-Induced Degradation can be easily discovered by using EL images. Although it is possible to detect PID from EL images, it is necessary to perform IV measurement again to estimate how much the power of the mega solar is reduced by PID. The authors are investigating a method to quantitatively estimate the power from the EL image. In this study, we evaluated Rsh of the PID module on a cell-by-cell basis and verified that the power could be estimated only by adjusting Rsh. Next, the correlation between the light emission from the EL image and Rsh was examined, and the power was estimated using Rsh estimated from the EL image. As a result, we were able to estimate the power with an error rate of about 3%. In addition, we found that the power can be estimated more easily by binarizing the amount of light emitted from the EL image and estimating Rsh.

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  • Toshiyuki HAMADA, Kenta NAKAMOTO
    2020 Volume 46 Issue 3 Pages 103-108
    Published: May 31, 2020
    Released: June 06, 2020
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    Photovoltaic systems cause electric shock accidents. Accidents have been reported wherein a firefighter who has extinguished a fire in a solar power generation facility has received an electrical shock. Additionally, there is a risk of electrical shock when touching a photovoltaic module scattered by wind. Specifically, rapid shutdown is popular in the USA to prevent electrical shock accidents during firefighting activities. When rapid shutdown is activated, the photovoltaic system enters a low voltage state. However, this rapid shutdown can only prevent electrical shock accidents during firefighting activities. Furthermore, to introduce rapid shutdown in established photovoltaic systems, the power conditioner may have to be replaced. Therefore, in this study, we propose a system that uses an electromagnetic relay to prevent electrical shock accidents and scattering of photovoltaic modules in photovoltaic systems, caused by fire extinguishing activities. The proposed system can be easily introduced into installed photovoltaic systems.

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