Due to the increased interest in the utilization of solar energy, it is essential to enhance the energy collection of solar energy devices. In this paper, a theoretical analysis of the instantaneous, daily, and yearly enhancement in solar energy collection of a tilted flat-plate solar collector augmented by a plane reflector is developed. The shadow effect due to the reflector on the collector is considered in the analysis. A FORTRAN computer program has been constructed based on the analysis in order to study the effect of different operational and design parameters of plane reflector-tilted flat-plate solar collector system on the collector solar energy collection. These parameters include collector-reflector system orientation and tilt angles, collector elongation ratio, and reflector overhang ratio. (C) 2000 Elsevier Science Ltd. All rights reserved.