Solar thermal systems use free heat from the sun to warm domestic hot water and can also supply your heating system. An ordinary boiler can be used to make the water hotter, or as a back-up to provide hot water when solar energy is unavailable. The system works by having solar panels called collectors usually fitted to the roof. These collect and convert the solar radiation into heat which is then transferred through pipes to a hot water cylinder. This system does not demand direct sunshine to operate so it will work all year round.
There are two types of panels, the flat plate panel and the vacuum tube panel. The flat plate panels are often preferred for looks over the tube collector. The vacuum tube panels consist of glass tubes in which the solar radiation is converted into heat. Mirrors behind the tubes concentrate the sun’s rays and the vacuum in the tubes allows almost no heat to escape. Because of this they are more efficient in the autumn, winter and spring than the flat plate panels.

Solar thermal can be used for heating systems (space heating). It is most effective for low temperature systems such as under floor heating. This can be achieved by installing more collectors on the roof and using a larger capacity thermal store instead of a normal solar hot water cylinder.
The biggest benefit of using solar thermal in conjunction with an underfloor heating system is the reduced energy bills. Once a solar thermal system is installed it has an extremely low running cost over its lifetime, so you can enjoy paying less for energy. This also means reducing your home’s carbon dioxide production and being able to rely less on utility providers.
Maintenance costs for solar water heating systems are generally very low. Most solar water heating systems come with a five-year or ten-year warranty and require little maintenance.

Via Science