Solar water heating systems use solar panels, called collectors, fitted to your roof. These collect heat from the sun and use it to heat up water which is stored in a hot water cylinder. A boiler or immersion heater can be used as a back up to heat the water further to reach the temperature you want.
There are two types of solar water heating panels:
Larger solar panels can also be arranged to provide some contribution to heating your home as well. However, the amount of heat provided is generally very small and it is not normally considered worth while.