A comparison of the economic viability of photovoltaic and diesel water pumping systems is presented for system sizes in the range 2.8 kWP to 15 kWp, Actual performance data from installed systems are employed for the base case. Sensitivity analysis is carried out to generalize results for other locations and conditions. The effect of system oversizing due to mismatch of water supply and demand patterns on the economic viability of PV water pumping system is illustrated based on real data and three-year operational experience of eight installations. Investment prospects in PV water pumping applications for different selling price scenarios of water have been investigated. (c) 2005 Elsevier Ltd. All rights reserved.