In this paper an energy balance model and simulation results are presented for a generic combined photovoltaic (PV) solar thermal (ST) system that incorporates phase change material (PCM). This is a promising integration of technology because the PV converts visible and ultra-violet parts of the solar spectrum, the ST utilises infra-red parts of the spectrum and waste heat from the PV, and the PCM reduces the temperature of the PV which increases PV efficiency. Parameters that are investigated cover PCM physical and thermal properties and water flow schemes. By including an appropriate PCM in an optimised system, the PV output can be increased by typically 9% with an average water temperature rise of 20 degrees C. Although any increase in PV performance has an associated decrease in ST performance, a practical and worthwhile compromise can still be achieved. This paper demonstrates that there is considerable scope for experimental realisation of the combined PV/ST/PCM system particularly if this is coupled with the development of PCMs with tuneable melting points and high thermal conductivity. (C) 2011 Elsevier Ltd. All rights reserved.