Module temperature dispersion within a large PV array: observations at the Amareleja PV plant

In-field photovoltaic (PV) module and array characterization is becoming increasingly important within the particular framework of quality assurance procedures at large commercial PV plants. In this context, the correct measurement of the module temperature is critical in order to reduce uncertainty and increase repeatability of results. In the case of large PV array characterization, the measurement provided by the sensors may not be representative of the PV array as a whole given the great diversity of operating conditions occurring throughout its surface area. Spatial temperature differences within a PV array of less than 5 K are typically considered in practice. However, the temperature differences observed at a commercial PV plant in Amareleja (Portugal) are more than twice those typically assumed. Such high differences may considerably increase the uncertainty in the determination of the PV array operating temperature and, hence, in its standard test conditions power characterization. This paper quantifies the uncertainty associated with the in-field measurement of the operating temperature of large PV arrays and their individual PV modules as a function of the type, number, and location of the temperature sensors used. Furthermore, the incident irradiance and particular wind speed conditions over the PV array have been clearly identified as the main causes of these temperature differences, showing that the optimum conditions to perform the PV array characterization do not correspond to low wind speed conditions, as recommended by many authors