Performance Assessment of PV Modules - Relationship Between STC Rating and Field Performance

PV module field performance can be assessed by annual effective efficiency and module performance ratio. The module specific data may be represented with normalized conversion efficiency as a function of irradiance at the average daylight ambient temperature. We demonstrate how to calculate annual performance ratio and present results for six PV modules at two locations and different tilts. Results are only weakly dependent on the specific location, the tilt angle of the module or normal variations in the spectral distribution. They depend on average annual daylight temperature, but only very weakly on the temperature distribution. The two key module parameters that control the effective efficiency are series resistance and leakage conductance. Effect of their variation is quantitatively determined. Discussion on different approaches for PV module energy rating is given