The effect of capacitance on high-efficiency photovoltaic modules: a review of testing methods and related uncertainties

Abstract

Abstract The effect of solar cell capacitance in the electrical characterization of photovoltaic (PV) modules at Standard Test Conditions (STC) is known since the 1990s. With the efficiency of solar modules increasing in the years, the corresponding measurement artefact has been generally resolved with long pulse simulators, from few milliseconds in the 2000 s and up to hundred milliseconds nowadays. With the last improvements in module technology, with the growing interest in n-type silicon and silicon heterojunction, and with the increasing wafer and cell sizes, it is demonstrated that even 100 ms simulators are no longer enough for accurate direct I–V measurements. The need for continuous simulators is therefore becoming more frequent even for accurate measurement of commercial size modules. This work summarizes the basic physics behind the effect of capacitance on the electrical characterization of silicon PV modules, with the simplest approach of a single diode capacitive model and with examples from high efficiency modules commercially available. It reviews eight measurement methods to mitigate the effect for accurate electrical characterization at STC; finally, it presents a novel and comprehensive analysis of the uncertainty contribution to the maximum power and open-circuit voltage determination of these measurement methods. The paper is a review of the best practices in advanced testing laboratories of silicon PV modules nowadays, and it represents a contribution addressed to metrologists, researchers and module manufacturers.