A photovoltaic (PV) powered water pumping system with water storage facility is being investigated with respect to some technical, meteorological, and operational conditions. The impacts of the pump efficiency, the electrical efficiency of the driving system, solar intensity, ambient air temperature, minimum and maximum water storage, and load variation on the PV generator size were studied. The study used a computer program based on the optimal sizing method investigated by the author. The system under consideration is intended to be used initially at Giza, Egypt (30 deg. longitude, 30 deg. latitude). The results showed that changing the pump efficiency from 20° to 35° will reduce the generator size from 15 to 8.6 kW peak, while changing the electrical efficiency of the pump drive system from 55° to 90° will change the generator peak power from 15.5 to 10 kW. Changing the minimum storage capacity from 250 m3to 2,500 m3will reduce the generator size from 10.84 to 10 kW, while changing the maximum storage capacity from 250 to 2,500 m3will increase the generator size from 10 to 10.84 kW peak. Changing the location from north Egypt to south will lead to generator size deviation of about 23 ° due to change in ambient air temperature and solar intensity. Finally, the study showed that for load variation from 0 to ±75° from the mean yearly load the increase in generator size will reach 30° with the minimum value at ±27.5° load variation.