Solar thermal systems heat water up to 65°C + using free energy from the sun. Solar can provide domestic hot water, space, process and pool heating. The two most popular types are flat plates and evacuated tubes. Evacuated tubes tend to be more efficient in cold climates or for higher water temperatures, such as Domestic hot-water storage.

In contrast, flat plate collectors tend to be more efficient in mild climates. Solar thermal is an excellent supplement to a heating system with good financial paybacks. Still, it can rarely operate as a standalone energy source and needs the addition of other energy sources and storage systems to provide a complete heating solution.