System Yield and Performance
The use of appropriate performance parameters facilitates the comparison of grid-connected Photovoltaic (PV) systems that may differ with respect to design, technology, or geographic location. Four performance parameters that define the overall system performance are final PV system yield, reference yield, performance ratio, and PV for Utility Scale Applications rating. The Photovoltaics for Utility Scale Applications (PVUSA) rating method uses a regression model and system performance and meteorological data to calculate power at PVUSA test conditions (PTC), where PTC are defined as 1000 W/m plane-of-array irradiance, 20°C ambient temperature, and 1 m/s wind speed. PTC differ from standard test conditions (STC) in that its test conditions of ambient temperature and wind speed will result in a cell temperature of about 50°C, instead of the 25°C for STC. The difference between the nameplate direct current (DC) power rating and the system PVUSA rating is an indication of the total system losses associated with converting DC module energy into actual current energy.