Performance analysis of photovoltaic installations in a Solar America City

We present our findings from a recent analysis of monitoring data collected on over 480 residential and commercial PV installations in Austin, Texas between 2005 and 2008. These systems were installed under a city rebate program administered by the city-owned electric utility, Austin Energy, and recognized under the Solar America initiative. The majority of these systems were residential installations with rated power under 4kW. In conjunction with the utility, we have undertaken an analysis of the accumulated data in order to quantify long-term performance. The primary analysis goals were to statistically compare the output of existing installations to predictions based on the PVWatts calculator developed by the National Renewable Energy Laboratory (NREL), and to identify trends linking underperforming or over-performing installations. In addition, we wished to establish a simple methodology for the utility to use in assessing the long-term performance of residential and commercial PV installations.