Accurate hourly photovoltaic (PV) output data are useful for engineering design, cost-effectiveness evaluation, rate design, system operation, transmission planning, risk management, and policy analysis. However, a large sample of hourly metered PV data is seldom available, and engineering simulation is often the only practical means to obtain hourly PV output. Based on an analysis of net energy metering (NEM) funded by the California Public Utilities Commission (CPUC), this paper presents statistically adjusted engineering (SAE) modeling of metered output of 327 roof-top PV installations in California for the 12-month period of January December 2008. The key findings are: (a) the metered PV output is on an average 80-90% of simulated performance; and (b) the simulated data have useful information for accurately predicting metered PV performance. Plausible causes for (a) include incomplete input data for PV simulation, occasional failures in metered data recording, and less than ideal conditions for PV performance in the real world. (C) 2010 Elsevier Ltd. All rights reserved.