Solar collectors have come a long way since the early experiments with radiators working in reverse, painted black! Nowadays the panels contain sophisticated materials that absorb and retain more heat, but essentially the principle is the same: heat from the sun (even on a cloudy day) is absorbed and transferred to a working fluid, usually a water/glycol mix. This fluid is then piped to a coil in your hot water tank to heat your domestic hot water. Collectors come in two types - flat plate and evacuated tube. Flat plate collectors can be integrated into the roof in a similar way to a 'velux' window or sit slightly proud; evacuated tube collectors are more efficient and take up less roof space.

A typical system comprises collectors, usually sited on a south-facing roof, a twin coil cylinder (one coil for the solar system and one for a conventional boiler) and a control station. The cylinder will usually fit inside an airing cupboard and can be unvented (supplies mains-pressure hot water) or vented. Integrating solar with combi boilers can be problematic and usually require the use of a cylinder.

Energy-saving installations attract a reduced rate of VAT at 5%.