Solar Trade Association.
below is a really handy video explaining the principles of solar thermal hot water production, it is produced by an American company which it why it features their details at the end.
If you have ever left your car parked on a sunny day and returned to it an hour or so later, you will have experienced solar heating as the car will be considerably warmer than the outside temperature.
Solar hot water is carbon free, sustainable and good for the environment.
Solar collectors are usually fastened to the roof, so that they are out of he way and receive the full benefit if the sun. A mixture of water and glycol circulates through the collectors and it is warmed by the sun (in the same way your car was). Collectors can be as simple as an old radiator painted black or as sophisticated as evacuated tubes, the latter are more efficient collectors but more expensive.
Solar thermal systems will not provide all of your hot water throughout the year but 60% and above is a reasonable expectation. The life expectancy of solar panels is well in excess of 20 years.