The technique of energetic optimization is employed to investigate the optimal performance of an irreversible hybrid air-conditioning/heat pumping system consisting of a vapor compression refrigerator cascaded with a solar-driven absorption refrigerator. To get closer to a real system, the effect of internal irreversibilities on the performance of the hybrid system is considered. The optimal operating temperature of the solar collector and the maximum overall coefficient of performance (COP) of the cooling and heating modes of the system are derived. The results obtained here have more realistic meaning than those of reversible thermodynamics for the optimal design and operation of practical solar-driven hybrid systems. (C) 2001 Elsevier Science Ltd. All rights reserved.