Actual issues on power measurement of photovoltaic modules

By Paul Grunow, Cofounder, PI Berlin AG; Alexander Preiss, PV-Outdoor Laboratory, PI Berlin AG, University of Technology Berlin; Michael Schoppa, Head of the PV-testing Laboratory, PI Berlin AG; Stefan Krauter, PI Berlin AG, University of Technology Berlin, University of Applied Sciences Biberach

Power measurements of PV reference modules can, at standard testing conditions (STC), show tolerance deviations of up to ±3%, greatly affecting the maximum power output and thereby lowering the overall energy yield of the installation. Despite some existing technical problems, there is an urgent need on the part of the photovoltaic community to achieve more accuracy in power measurements in respect to the ever-growing production volumes. Some approaches being undertaken to carry out high-quality power measurements are addressed in this paper. The deviation from an ideal simulator performance are shown and discussed for two types of simulators, with reference to the most relevant parameters: irradiance level, deviation from homogeneity, spectral mismatch and temporal stability.