Indirect Measurement of Photovoltaic Module Temperature Using Open-Circuit Voltage Under Variable Irradiance

Abstract

The operating temperature of a photovoltaic module strongly affects its electrical performance, while direct temperature measurements may be influenced by sensor placement, thermal resistance, and measurement delay. This paper investigates the use of open-circuit voltage for estimating the temperature of a photovoltaic module under varying irradiance conditions. Two standard-based approaches, derived from IEC 60904-5 and EN 50530, are compared with a proposed empirical model in which the temperature sensitivity of the open-circuit voltage is allowed to vary with irradiance. The experimental study was carried out using a water-cooled 10 W polycrystalline PV module. A total of 135 I–V characteristics were measured at 15 irradiance levels between 72 and 834 W/m2 and at nine module temperatures between 30 and 70 °C. The parameters of all investigated models were identified from the experimental data, and their temperature estimation performance was evaluated over the complete measurement range. The standard-based methods provided satisfactory results mainly at medium and high irradiance levels, whereas their accuracy decreased at low irradiance. The proposed model accounted for the irradiance dependence of the open-circuit voltage temperature sensitivity and reduced the estimation error over the investigated operating range. The obtained RMSE was 0.26 °C, with a mean absolute error of 0.21 °C and a maximum absolute error of 0.82 °C. These results indicate that the proposed approach can provide a simple method for indirect PV module temperature estimation in monitoring and control applications.