PV module energy rating: opportunities and limitations

This article sheds new light on photovoltaic (PV) module rating according to predicted yield rather than power measured at standard testing conditions (STC). We calculate module performance ratios (MPR) for measured characteristics of eight different module types and compare them with a reference MPR calculated with typical crystalline silicon characteristics. In place of the not yet existing standardized weather data, we use commercially available weather data for three different locations. The reference MPR for the three locations were 95.5%, 94.6%, and 91.0%, respectively, with differences to the other module types of +/- 8% at maximum. MPR was calculated with reference to nominal power, and-following IEC 61853 -without consideration of potential degradation. The strongest contribution to the initial differences between the module types was due to differences in irradiance dependency. Standard uncertainties for all initial MPR values were calculated and range from 1.8% to 3.0%, including STC power uncertainty. We propose a module rating method that indicates whether a module type's performance is significantly above, below, or essentially equal to the reference. The method evaluates the MPR difference between module type and reference, taking uncertainty into account. Significant differences were only found between modules with obviously different characteristics, but not between the crystalline silicon module types under scrutiny. As the uncertainty analysis did not cover degradation and influences due to the use of not standardized weather data, a sensitivity analysis was performed. Long-term degradation can change the comparative energy rating significantly, whereas the selection of tilt angle and assumptions regarding module operating temperature did not have a strong effect. Copyright (C) 2015 John Wiley & Sons, Ltd.