Various concepts of combined PV-thermal collectors are possible. These concepts differ in their approach to obtain the maximum yield and it is not easy to say whether the yield of a complicated design will be substantially higher than the yield of a simpler one. In order to obtain a clearer view on the expected yield of the various concepts, nine different designs were evaluated. The channel-below-transparent-PV design gives the best efficiency, but since the annual efficiency of the PV-on-sheet-and-tube design in a solar heating system was only 2% worse while it is easier to manufacture, this design was considered to be a good alternative. (C) 2003 Elsevier Ltd. All rights reserved.