A thermal model for open-rack mounted photovoltaic modules based on empirical correlations for natural and forced convection

Abstract

This paper proposes a thermal model for calculating the temperature of open-rack mounted photovoltaic (PV) modules taking into account the meteorological conditions, position (i. e. the inclination of one PV module and the angle between its surface and wind direction) and technical characteristics of the PV modules. The present model is valid for the steady-state operation and is based on the energy balance equation in which the forced convection is modelled by the new empirical correlations. The possibility of occurrence of the flow separation along the surfaces of the PV modules is included in these correlations. The effect of the angle between the wind direction and the PV module plane, which is usually ignored in the modelling of forced convection, is also taken into consideration. In this manner, it is possible to estimate the temperature of PV modules more precisely, as well as to determine the power and efficiency which depend on the temperature. For four particular PV modules, it is found that the temperatures, obtained using the proposed thermal model, are in good agreement with the corresponding measured temperatures. Compared with the other models commonly used for thermal analysis of PV modules (SNL and NOCT-based correlations), this model yielded better results. The deviation of the PV module temperature calculated using the proposed thermal model from the measured one is up to 2°C, and the deviations of the PV module temperatures calculated using the SNL and NOCT-based correlations from the measured ones amount up to 5°C and 20°C, respectively, depending on the PV module type and ambient conditions.