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Specific energy yield of low-power amorphous silicon and crystalline silicon photovoltaic modules in a simulated off-grid, battery-based system
Some amorphous silicon (a-Si) photovoltaic (PV) manufacturers claim that their power ratings at standard test conditions (STC) understate the performance of their modules because of a-Si technology’s ability to achieve 10-15% higher energy yield per rated peak power (WP) than crystalline silicon (c-Si) technology. I tested this claim in a simulated off-grid, battery-based system through a 12-month study of the energy yield of five a-Si and five c-Si PV modules with ratings between 14 to 20 WP. The test was conducted in Arcata California, with a climate characterized by mild, rainy winters and dryer, often foggy, summers. The specific energy yield (energy yield per tested WP) of the different types of modules was correlated to temperature, insolation, and clearness index (C.I.) data and compared between the groups and between individual modules. The a-Si group outperformed the c-Si group in specific energy yield (Wh/WP) over the 12-month period by 2.7%. While it was statistically difficult to isolate the effects of temperature and C.I. on specific energy yield, the results indicated that the a-Si group’s higher specific energy yield is due more to better performance in higher temperatures rather than in low C.I. conditions. Two reasons that may account for a lower difference in specific energy yield than reported in previous studies are Arcata’s mild climate and the absence of a maximum power point tracker in the system. Both the best and worst performing individual modules were a-Si, which illustrates that individual module quality can outweigh any improved performance of a-Si technology.