There are two types of solar water heaters on the market
FPC (flat plate collector) system: the flat plate collector system is a metal system. They consist of an insulated metal box covered with armoured glass. There is a layer of copper on the metal box, which can absorb heat well.The copper plate is also coated with a black coating to improve heat absorption.The metal box contains copper tubes arranged vertically and connected by two horizontal copper tubes (called header) at the top and bottom. Cold water enters the collector (golden box) from the bottom pipe and then rises into the vertical pipe. It is heated in a vertical pipe. As the water is heated, it becomes lighter (hot water is lighter than cold water), and the water rises and is collected into the storage tank through a top horizontal pipe (or header). Now you can use the water.