A flat plate solar water heater is a type of solar thermal system that uses flat solar collectors, typically made of metal or glass, to absorb solar energy and convert it into heat. The heat is then transferred to water or a fluid that is circulated through the solar collectors and stored in an insulated storage tank. Flat plate solar water heaters are often used for residential and commercial hot water systems, and can be used in both active and passive systems. In an active system, a pump is used to circulate the fluid between the solar collectors and the storage tank, while in a passive system, the fluid is circulated through the solar collectors and the storage tank through natural convection. Flat plate solar water heaters are typically more efficient than other types of solar water heaters and can be used in a variety of climates.