You use hot water at home every day when you take a shower, run a load of laundry, or wash your dishes. Solar water heating systems use the sun’s energy to heat the water in your home.
Solar hot water (also known as solar water heating) is an alternative to conventional water heating systems, including tank-less coil water heaters, gas water heaters, electric water heaters, or heat pump water heaters (all of which use either gas, oil, or electricity to power them.) We have used solar energy to heat water for centuries, but not until the 1980s did solar hot water companies begin to take off, making solar hot water a viable option for property owners.
Roof mount solar hot water systems are also referred to as ‘close-coupled’ systems.
These comprise a water tank attached to solar collectors sitting on the roof. The water from the tank is flows into the panels, where it heats before it goes back up into the tank.
Most homeowners who have heat pumps use them to heat and cool their homes. But a heat pump also can be used to heat water — either as stand-alone water heating system, or as combination water heating and space conditioning system.
You can purchase a stand-alone heat pump water heating system as an integrated unit with a built-in water storage tank and back-up resistance heating elements.
The panels in a solar thermal system are known as “collectors,” and are typically installed on a rooftop. These collectors are different from the photovoltaic solar panels you’re probably familiar with, because instead of generating electricity, they generate heat. Sunshine (or “solar radiation”) passes through a collector’s glass covering and strikes a component called an absorber plate, which has a coating designed to capture solar energy and convert it to heat. This generated heat is transferred to a “transfer fluid” (either antifreeze or potable water) contained in small pipes in the plate.
Collectors come in different sizes. The size and number of collectors you’ll install depends on how much sunshine your roof gets and how much hot water you use in your home. They are also made in two styles: flat plate and evacuated tube. Flat plate collectors are generally less expensive, but can capture less sunlight and are less efficient in colder conditions. Evacuated tube collectors take up less space on your roof, but are heavier and more fragile.
Most solar hot water systems have a controller system that ensure the water in the storage tank doesn’t get too hot. Controller systems can also prevent cold water from being cycled through the system when it’s extremely cold outside and the transfer fluid isn’t being warmed sufficiently.