In summary, a very simple but accurate procedure to model the photovoltaic water pumping system has been presented. The procedure is applied to the Solar Star 1000 pumping system to arrive at a model that predicts the volume ¯owrate, given the head and the irradiance. The model predicts the ¯owrates to within 8% of the measured values. The deviation, though small, is attributed to ¯uctuations in the solar irradiance and unsteady module temperatues during the measurement