The energy balance of photovoltaic (PV) cells is modelled based on climate variables. Module temperature change is shown to be in a non-steady state with respect to time. Theoretical expressions model the energy transfer processes involved: short wave radiation, long wave radiation, convection and electrical energy production. The combined modal is found to agree well with the response of the measured model temperature to transient changes In irradiance. It is found that the most precise fit to measured data is obtained by fitting the value of the forced convection coefficient for module convection. The fitted values of this coefficient were found to br within the range predicted by previous authors. Though the model is found to be accurate to within 6 K of measured temperature values 95% of the time in cloudy conditions, best accuracy is obtained in clear and overcast conditions when irradiance is subject to less fluctuation. (C) 2001 Elsevier Science Ltd. All rights reserved.