Assessment on the variation of temperature coefficients of photovoltaic modules with solar irradiance

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• Temperature coefficients (TC) of PV modules were evaluated in different irradiances. • TC of V oc varies logarithmically with irradiance for c-Si PV modules. • A novel empirical function is derived to calculate the TC of V oc in any irradiance. • An improved description of PV module behavior under different irradiance is shown. In PV system performance models, the change in temperature coefficients (TC) as a function of solar irradiance ( G ) is usually not calculated. Although the variation of the TC of open circuit voltage ( V oc ) with G is predicted by solar cell theory, most performance models do not account for this behavior. Equations describing the variation of TCs with G are not readily available. The main objective of this paper is to experimentally evaluate the variation of TCs with G of crystalline silicon PV modules. Several I-V curves were measured, with G ranging from 100 to 1000 W/m 2 and module temperature ranging from 25 to 65 °C. A matrix of 50 I-V curves was obtained for each PV module and TCs were calculated for different G values. The TC of the short-circuit current ( I sc ) is practically constant with G , except for two studied half-cell PV modules. The absolute value of TC of maximum power ( P m ) increases for lower irradiance values for most modules tested, but this trend is not seen for two recently manufactured PV modules where a negligible variation with G was obtained. The main result is a new logarithmic function that fits the experimental data and shows a well-defined increase in the modulus of the TC of V oc for low irradiance values. The equation proposed to describe this behavior is a novelty to improve PV device modeling. The results presented here contribute to a better understanding of TCs under varying irradiance, an important aspect of PV module performance.