But, there is something not as popular but works just as well and looks virtually the same. A solar water heater. They have these little tubes that hold liquid and sit out in the sun all day. When they get hot it moves back into the house and the system.
The systems are fairly straightforward. The liquid in the tubes then heats up the water in your tank so you don't have to use the heater. Although for cloudly days most have a backup heater. They also have little controls to keep the water from getting too hot.
It is a very catchy little system, and great if you are just started a home, since it isn't too much more than is already going into the home. It can also be added to a home, but you'd have to look into your current bills to see if the payoff time was okay for you.