A transient simulation model, using TRNSYS, for AC photovoltaic (PV) water pumping systems is developed and validated against laboratory and field data. Simulations and analysis were undertaken in this work to: (i) discern the influence of mismatch of pump characteristics and well system characteristics on system performance; (ii) obtain average efficiencies and average performance ratios for system, subsystem and PV array over any period of time and under different operating conditions; (iii) analyze the effect of insolation frequency distribution on system performance and (iv) determining the optimum PV array size considering life cycle cost analyses. Simulation and analyses are illustrated using a real case study and utilizing real field data obtained from a system installed in Jordan. (c) 2005 Elsevier Ltd. All rights reserved.