This paper presents performance and reliability data from nearly 50,000 photovoltaic (PV) systems totaling 1.7 gigawatts installed capacity in the USA from 2009 to 2012 and their geographic trends. About 90% of the normal systems and about 85% of all systems, including systems with known issues, performed to within 10% or better of expected performance. Although considerable uncertainty may exist due to the nature of the data, hotter climates appear to exhibit some degradation not seen in the more moderate climates. Special causes of underperformance and their impacts are delineated by reliability category. Hardware-related issues are dominated by inverter problems (totaling less than 0.5%) and underperforming modules (totaling less than 0.1%). Furthermore, many reliability categories show a significant decrease in occurrence from year 1 to subsequent years, emphasizing the need for higher-quality installations but also the need for improved standards development. The probability of PV system damage because of hail is below 0.05%. Singular weather events can have a significant impact such as a single lightning strike to a transformer or the impact of a hurricane. However, grid outages are more likely to have a significant impact than PV system damage when extreme weather events occur.
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