This product is designed to help you heat your pool without the need for costly electricity. Our solar powered pool heaters use the power of the sun to provide a reliable and efficient way to keep your pool warm. With no need for wiring or installation, these heaters are easy to use and
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.