Solar water heaters also called solar domestic hot water systems — can be a cost-effective way to generate hot water for your home. They can be used in any climate, and the fuel they use — sunshine — is free.
How They Work

Solar water heating systems include storage tanks and solar collectors. There are two types of solar water heating systems: active, which have circulating pumps and controls, and passive, which don’t.
Active Solar Water Heating Systems

There are two types of active solar water heating systems:

Direct circulation systems
Pumps circulate household water through the collectors and into the home. They work well in climates where it rarely freezes.
Indirect circulation systems
Pumps circulate a non-freezing, heat-transfer fluid through the collectors and a heat exchanger. This heats the water that then flows into the home. They are popular in climates prone to freezing temperatures.