Effects of synchronous irradiance monitoring and correction of current–voltage curves on the outdoor performance measurements of photovoltaic modules

Precise outdoor measurement of the current–voltage (I–V) curves of photovoltaic (PV) modules is desired for many applications such as low-cost onsite performance measurement, monitoring, and diagnosis. Conventional outdoor measurement technologies have a problem in that their precision is low when the solar irradiance is unstable, hence, limiting the opportunity of precise measurement only on clear sunny days. The purpose of this study is to investigate an outdoor measurement procedure, that can improve both the measurement opportunity and precision. Fast I–V curve measurements within 0.2 s and synchronous measurement of irradiance using a PV module irradiance sensor very effectively improved the precision. A small standard deviation (σ) of the module's maximum output power (P max) in the range of 0.7–0.9% is demonstrated, based on the basis of a 6 month experiment, that mainly includes partly sunny days and cloudy days, during which the solar irradiance is unstable. The σ was further improved to 0.3–0.5% by correcting the curves for the small variation of irradiance. This indicates that the procedure of this study enables much more reproducible I–V curve measurements than a conventional usual procedure under various climatic conditions. Factors that affect measurement results are discussed, to further improve the precision.