Solar water heaters operate in one of two ways: either as a direct system or as an indirect system. A direct system warms water by circulating it via pipes through rooftop solar collectors. An indirect system, also known as a closed-loop system, relies on a non-freezing heat transfer liquid. The liquid is heated in the solar collectors and returns through pipes to a storage tank, where a heat exchanger inside the tank transfers the heat to the water. Most systems rely on electric pumps to move water (or a transfer liquid) between the storage tank and the rooftop solar collectors. In general, solar water heaters can be used anywhere as long as your roof gets direct sunlight for most of the day. The rooftop collectors should face south. A direct system makes sense in warm climates where temperatures don’t fall below freezing. The non-freezing liquid used in an indirect system makes it better suited for cold climates.
You’ll need to retain your conventional water heater as a back-up at night, on cloudy days, or anytime your family needs more hot water than your system can produce. An average person uses about 15 to 20 gallons of water per day, so a family of four would likely need an 80-gallon water heater tank.