Precise Outdoor PV Module Performance Characterization Under Unstable Irradiance

Improvement in the precision of outdoor performance measurements of photovoltaic (PV) modules is investigated under wide ranges of irradiance and temperature conditions. Special care is taken for the measurement on partly sunny days, when the solar irradiance is unstable. Factors to affect the measurement uncertainty are discussed based on the procedure including fast current-voltage (I-V ) curve measurements within 0.2 s, simultaneous irradiance monitoring by a PV reference device designed for outdoor use, and precise module temperature measurement. It is demonstrated that the effect of temporal variation of irradiance on the I-V measurements can be suppressed to within ±0.4% even when the irradiance is unstable, by reducing the measurement time to 0.2 s. It is also shown that the spatial nonuniformity of irradiance within the PV module, and the difference of irradiance between the module and irradiance sensor, are among the residual factors to affect the performance measurements. Both of their impacts on the uncertainty of Pmax are estimated to be within about ±1% and ±2% at the irradiance levels of 1.0 and 0.4 kW/m2, respectively, for the present experimental setup. Other sources of uncertainty are also discussed.

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