Solar water heating is a cost-effective and environmentally friendly way to heat your home's water. This system uses the sun's energy to heat water, which is then stored in a tank for later use. Solar water heating systems are easy to install and maintain, and can save you money on
From Wikipedia
Solar water heating (SWH) is heating water by sunlight, using a solar thermal collector. A variety of configurations are available at varying cost to provide solutions in different climates and latitudes. SWHs are widely used for residential and some industrial applications.