Solar thermal traps the energy carried in daylight to heat hot water. Direct sunlight intensifies this effect. The three key technologies for doing this are evacuated tubes, unglazed collectors and flat plate collectors, but they mostly all work on the same simple principle; water from the cold supply provides the water which is used to travel to the solar collector which, using the suns energy, heats up the water. From here it travels back into a cylinder to be stored as hot water.
Domestic systems dominate the UK solar thermal market, but solar thermal has an important role to play in commercial heating and it can even deliver district and heating for industrial processes. For industrial processes solar thermal can deliver temperatures over 200 degrees centigrade!
For householders, solar thermal means an abundant supply of hot water in your hot water tank. Solar thermal can extend the life span of your boiler, because for most of the year your boiler will be used little. From March to September, solar will provide most of your water heating needs and then it will make a lower contribution during the winter months.
Solar thermal can work even on small roofs because it requires less space than solar PV. Solar thermal systems are also more affordable.
There are solar thermal systems which can be used for air heating (or cooling) but these are not yet common in the UK. The biggest misconception is that solar thermal can meet your domestic central heating requirements! If designed and sized accordingly, a solar thermal system can provide a contribution to your space heating (ideally through an under-floor heating system working at lower temperatures than traditional wall mounted radiators). However, you would need a hot water cylinder of around 600 litres minimum (preferably 1200-1500 litres) and a far greater collector area on your roof.
Today over 200GW of solar thermal are installed globally – thats double the current capacity of solar PV. 90% of Israeli households now rely on solar thermal for their hot water and solar thermal is common place in many EU homes.