A simple constrained optimization method is proposed. The objective function is the electrical output power, and the constraints are the current-voltage characteristic and the energy balance at the level of a series-parallel PV module. The influence of latitude and climate on PV module shape is significant. Optimized modules operating in warmer climates consist of a higher number of PV cells in series and a lower number of strings of PV cells than those operating in colder climates. Also, the ratio between the length and the width of an optimized PV module is over unitary at high latitudes and under unitary at low latitudes. The optimum PV module shape depends significantly on the quality of the PV cells. (c) 2005 Elsevier Ltd. All rights reserved.