Abstract A model for the simulation of photovoltaic d.c. solar pumping plants is presented. The model also includes simple meteorological data simulations. The computations are based on an energy balance at the pump input and take into account the effect of meteorological data on the array efficiency and the effect of the configuration instantaneous state on the subsystems efficiency. The results allow explanation of the morning/afternoon dissymmetry of the flow and show that the price of a cubic meter of water can be optimized to improve the benefit/cost ratio. The dissymmetry and the variation of the cubic meter price are explained as follows: small-sized plants are affected by the threshold effect of the pump, and large-sized plants work under a higher manometric head in the afternoon.