A mathematical model for making quantitative and qualitative predictions regarding the performance of water-cooled photovoltaic/thermal collectors integrated with a building domestic hot water preparation system has been developed. A genetic algorithm has been applied to the model in order to simultaneously find optimal design parameters affecting photovoltaic/thermal collectors' feasibility. For all formulated problems, Pareto optimal sets of conflicting solutions are obtained giving the designer information on the trade-off relationships between solutions. (C) 2014 Elsevier B.V. All rights reserved.