Tetsuyuki Ishii

A Methodology for Estimating the Effect of Solar Spectrum on Photovoltaic Module Performance by Using Average Photon Energy and a Water Absorption Band

Various photovoltaic (PV) technologies are commercially available today. The effect of solar spectrum on the performance of PV modules should be evaluated quantitatively in order to estimate the module performance with high accuracy and precision. Average photon energy (APE) has been frequently applied to evaluate the effect of solar spectrum. The purpose of this study is to enhance the precision and accuracy by introducing other indexes. In this study, we select solar spectra, the integrated spectral irradiance (ISI) and APE of which are equivalent to those of the standard AM1.5G spectrum. There is a slight difference in shape, although the shapes are approximately similar. We introduce one more index, which defines the spectral irradiance at the atmospheric window or the depth of the water absorption band. The introduction would further improve the accuracy and precision of the evaluation of the effect of solar spectrum.

Time-dependent changes in copper indium gallium (di)selenide and cadmium telluride photovoltaic modules due to outdoor exposure

The performance of photovoltaic (PV) modules deteriorates with time due to outdoor exposure. We investigated the time-dependent changes in PV modules and evaluated the amount of power generated during their lifetime. Once a year, the exposed modules were removed and measured under standard test conditions using a solar simulator. Their outputs were measured indoors and normalized to nominal values. In addition, the relationship between the indoor measurement and the energy yield for thin-film PV modules will be reported. In CIGS PV modules, the normalized maximum power (P MAX) and performance ratio (PR) differ with the type of module. The P MAX and PR of CdTe PV modules significantly decrease after outdoor exposure for three years. These results help to determine the characteristics of the time-dependent changes in the P MAX of PV modules due to outdoor exposure.

Development of a practical method of estimating electric power from various photovoltaic technologies with high precision

The purpose of this study is to develop a method of estimating the electric power from various photovoltaic technologies with high precision. The actual outdoor performance of eight kinds (12 types) of photovoltaic (PV) modules has been measured since January 2012 in order to verify the precision of the method. Using ambient climatic datasets including solar irradiance, module temperature, and solar spectrum, the performance of these PV modules is corrected to the performance under standard test conditions (STC), which should be constant ideally. The results indicate that the performance of bulk crystalline silicon (c-Si) and copper indium gallium diselenide (CIGS) PV modules can be estimated with high precision (approximately less than ±2%). However, the estimation precision of thin-film Si and cadmium telluride (CdTe) PV modules is low because of the initial light-induced degradation and seasonal variation due to metastability.