Solar water heaters vary in design, efficiency, capacity and price, but they all replace a good chunk of the gas or electricity used to heat water with clean, free sunlight. The three basic designs all have a way to collect heat, a tank to store hot water, backup heating for when your system cant keep up and a circulation system.

Batch collector water heaters heat water in tubes or pipes, usually painted black to collect more of the suns heat. Cold water can be mixed in periodically to keep water from getting too hot. These heaters are best suited for warmer climates. Where freezing might be an issue, theyll need to be drained during cold months to avoid damage to the system.

Flat-plate collectors rely on a metal plate, often painted black, to soak up the suns heat. Heat travels from the plate to water-filled tubes. The water cycles through heating tubes to and from the storage tank, keeping the stored water hot.

Evacuated tube collectors are the most efficient models out there. Water is heated in a tube thats surrounded by a larger, vacuum-sealed glass tube. Very little heat is lost because theres no air between the heating liquid and the outside world.

Solar water heaters can heat water directly or indirectly. In indirect heaters, the...