This paper presents theoretical and experimental analysis of the performance of a photovoltaic system supplying DC loads and controlled by either a cuk or a sepic converter.  The nonlinear mathematical model of the system is obtained, considering all operation modes of both converters. A fairly detailed nonlinear simulation was built to assess the performance when system is supplying constant and dynamic loads. Simulation and experimental results are presented illustrating both the steady state and the starting characteristics of the system. The relation between solar irradiation level and the duty ratio for both steady–state and run-up for the cuk and sepic converters have also been given to ensure maximum energy utilization. The results are presented in a comparative form which clearly illustrates that the cuk converter operates over a wider range of irradiation levels. The results also show that with a proper design of photovoltaic generator and careful selection of the dc-dc converter, the performance of a particular application can be optimized by controlling the converter duty ratio.