From Eric Kvaalen, Les Essarts-le-Roi, France
Paul Whiteley points out that 75 per cent of the sunlight hitting solar panels is lost as heat, but roof-top solar water heaters convert 95 per cent into hot water. So let’s combine the two! Have a layer of water between the solar panel and a glass plate, as in a solar water heater. The sunlight passes through the glass and water, and some 20 per cent of it is turned into electricity. The rest becomes heat, most of which is captured by the water. Install enough of these versions to provide your hot water, plus some normal panels to obtain more electricity if needed (Letters, 10 January).
