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The performance of photovoltaic (PV) modules is generally rated under standard test conditions (STC). However, the performance of thin-film photovoltaic modules is not unique even under STC, because of the “metastability”. The effects of the light soaking and thermal annealing shall be incorporated into an appropriate energy rating standard. In this study, the change in I–V characteristics of thin-film PV modules caused by the metastability was examined by repeated indoor measurements in addition to round-robin outdoor measurements. The investigated thin-film modules were copper indium gallium (di)selenide (CIGS), a-Si : H, and a-Si : H/µc-Si : H (tandem) modules. The increase in the performance of the CIGS module between the initial and final indoor measurements was approximately 8%. Because of light-induced degradation, the indoor performance of the a-Si : H and a-Si : H/µc-Si : H modules decreased by approximately 35% and 20%, respectively. The performance was improved by about 4–6% under high temperature conditions after the initial degradation. The results suggest that the performance of thin-film silicon modules can seasonally vary by approximately 4–6% only due to thermal annealing and light soaking effects. The effect of solar spectrum enhanced the outdoor performance of the a-Si : H module by about 10% under low air mass conditions, although that of the a-Si : H/µc-Si : H modules showed a little increase. The currents of these a-Si : H/µc-Si : H modules may be limited by the bottom cells. Therefore, it is required to optimize the effect of solar spectrum in addition to the effects of light soaking and thermal annealing, in order to achieve the best performance for thin-film silicon tandem modules. Copyright © 2013 John Wiley & Sons, Ltd.

Photovoltaic (PV) systems have become popular globally as an important candidate in the establishment of low-carbon electrical and civil systems. Since the early 1990s, globally, many PV systems have been installed, and their performance parameters such as annual yield, performance ratio, and system losses have been monitored in order to understand their basic characteristics; these data also help in the development of these systems and in analyzing their reliability. In Japan, the performance of residential PV systems was evaluated and reported. However, these evaluations were carried out using older systems, and the current status and the performance trend for each installation year have not been sufficiently evaluated and discussed. Therefore, this report aims to provide a macroscopic evaluation of the performance trends of PV systems by using the monitoring data of systems that were installed between the year 2000 and the year 2007. As a result of the evaluation, we have concluded that the performance ratio of these systems improved to an average of 0.72 until fiscal year 2000 and to 0.78 after fiscal year 2001. For investigating the factors behind this increase in performance ratio, we have focused on characteristics of the actual system capacity (capacity of each PV module measured at the point of shipment) and inverter efficiency. Copyright © 2010 John Wiley & Sons, Ltd.

The performance of six photovoltaic (PV) modules composed of polycrystalline silicon (pc-Si), amorphous silicon (a-Si), and hydrogenated amorphous silicon/crystalline silicon (a-Si:H/c-Si) modules was investigated at eight locations in Japan from August 2007 to December 2008. In addition, solar irradiance, solar spectrum, and module temperature were simultaneously measured in these round-robin measurements. In this study, we evaluate quantitatively the effects of module temperature and solar spectrum on the performance of the PV modules as thermal factor (TF) and spectral factor (SF), respectively. Furthermore, we investigate the variation in module performance, which is converted into module performance under standard test conditions (STC) using the TF and SF. In the case of the pc-Si modules, the variations in performance ratio under STC (PRSTC) for these modules range from 0.056 to 0.074 through the round-robin measurements. The TF indicates that the contribution of module temperature to the variation in performance is large, between about 15 and 20%. However, the SF suggests that the contribution of solar spectrum is quite small, less than 3%. In the case of the a-Si modules, the contribution of module temperature is about 8%. The performance is largely influenced by solar spectrum, more than 12% at its maximum. Consequently, the variations in the corrected PRSTC of the a-Si modules are between 0.117 and 0.141. These large variations may result from the effects of thermal annealing and light soaking. The variation in PRSTC of the a-Si:H/c-Si module is similar to that of the pc-Si modules. Copyright © 2010 John Wiley & Sons, Ltd.

In order to disseminate Photovoltaic (PV) technologies into the energy network, the cost down is not only important, but also improving the performance of the PV system is significant issues. Long-term reliability is one of the most important issues in terms of PV system performance. Previous researches were mainly focused on the reliability of PV modules, but the PV system is composed of a power conditioner, wiring, junction box, and so on. To improve the reliability of PV systems, it is important to accumulate trouble cases focused on all components of PV system. In this paper, we aim at evaluation of the reliability for the PV system on the early stages of PV system's lifetime by using large number of Japanese PV systems' data from the field Test in Japan. New Energy and Industrial Technology Development Organization has been running the “Field test project in Japan” from 1992. In this project, PV system users have cooperated with the collection of monitoring data and reported on the information of maintenance and certain failures of PV systems for 4 years after installation of PV system. Using those reports each year of installation, we evaluated reliability of PV systems by means of parameters such as Mean Time Between Failure, Mean Time To Repair, and the suspension time of PV system. As a result, the main trouble of PV systems was related power conditioner, and a few trouble of PV module was caused by typhoon. Moreover, the trend of the failure rate before FY 2000 of installation was demonstrated as the trend of initial failure in “bathtub curve;” however, the trend of its after FY 2001 of installation was indicated as the accidental failure in “bathtub curve.” Further, the operator simply forgot to restart the power conditioner after maintenance or suspensions of PV system in many trouble cases, and the user did not notice that it had been suspended for a while. These trouble cases can be avoidable easily through the effective alarm such as error message of power conditioner systems with monitoring systems. Thereby, monitoring with the evaluation method of PV systems is one of the important technologies due to the long-term reliability and stable operation. Copyright © 2010 John Wiley & Sons, Ltd.

Here, we present the results of evaluation of solar energy potential and photovoltaic (PV) module performance from actual data measured over a period of more than 2 years in the Gobi Desert of Mongolia. To allow estimation of solar energy potentials and durability of PV systems in the Gobi Desert area, a data acquisition system, including crystalline silicon (c-Si), polycrystalline silicon (p-Si) modules, and two sets of precision pyranometers, thermometers, and anemometer, was installed at Sainshand City in October 2002. This system measures 23 parameters, including solar irradiation and meteorological parameters, every 10 min. High output gain was observed due to operation at extremely low ambient temperatures and the module performance ratios (PRs) were high (>1·0) in winter. In summary, the present study showed that a PV module with a high temperature coefficient, such as crystalline silicon, is advantageous for use in the Gobi Desert area. Copyright © 2006 John Wiley & Sons, Ltd.

Under the auspices of the New Sunshine Program and continuous RD 975 h in 2000, 982 h in 2001 and 975 h in 2002, and the mean value of the performance ratio was over 70%; 73·3% in 2000, 71·8% in 2001 and 72·5% in 2001. Copyright © 2004 John Wiley & Sons, Ltd.

The performance of photovoltaic modules is influenced by solar spectrum even under the same solar irradiance conditions. Spectral factor (SF) is a useful index indicating the ratio of available solar irradiance between actual solar spectrums and the standard AM1·5-G spectrum. In this study, the influence of solar spectrum on photovoltaic performance in cloudy weather as well as in fine weather is quantitatively evaluated as the reciprocal of SF (SF−1). In the cases of fine weather, the SF−1 suggests that solar spectrum has little influence (within a few %) on the performance of pc-Si, a-Si:H/sc-Si, and copper indium gallium (di)selenide modules, because of the “offset effect”. The performance of a-Si:H modules and the top layers of a-Si:H/µc-Si:H modules can vary by more than ± 10% under the extreme conditions in Japan. The seasonal and locational variations in the SF−1 of the bottom layers are about ± several %. A negative correlation is shown between the top and bottom layers, indicating that the performance of a-Si:H/µc-Si:H modules does not exceed the performance, at which the currents of the top and bottom layers are balanced, by the influence of solar spectrum. In the cases of cloudy weather, the SF−1 of the pc-Si, a-Si:H/sc-Si, and copper indium gallium (di)selenide modules is generally higher, suggesting favorable for performance than that in fine weather. Much higher SF−1 than that in fine weather is shown by the a-Si:H module and the top layer of the a-Si:H/µc-Si:H module. The SF−1 of the bottom layer neither simply depend on season nor on location. Copyright © 2011 John Wiley & Sons, Ltd.