A solar water heating system using evacuated tubes installed at the George Washington University in Washington, DC (Photo courtesy of Skyline Innovations)
Solar heating & cooling (SHC) technologies collect the thermal energy from the sun and use this heat to provide hot water, space heating, cooling, and pool heating for residential, commercial, and industrial applications. These technologies displace the need to use electricity or natural gas. Today, Americans across the country are at work manufacturing and installing solar heating and cooling systems that significantly reduce our dependence on imported fuels. We need smart policies to expand this fast‐growing, job‐producing sector.
The U.S. Solar Heating & Cooling Alliance is a division of SEIA focused on growing the solar heating & cooling market through reducing barriers and advocating for policies on the federal, state, and local levels. To learn more about the SHC Alliance, click here.
Did You Know? Solar Heating & Cooling Fast Facts
- Solar water heating systems are affordable for families. The return on investment can be as little as 3-6 years, the lowest of any solar technology. Commercial systems help companies reduce and manage their energy bills, managing long-term costs. Meanwhile, fossil fuel prices fluctuate considerably and are expected to rise significantly over the next decade.
- Water heating, space heating, and space cooling accounted for 72 percent of the energy used in an average household in the U.S. in 2010 ‐ representing a huge market potential for solar heating and cooling technologies!
- In 2010, the U.S. saw 35,464 solar water heating systems and 29,540 solar pool heating systems installed, heating a total of more than 65,000 homes, businesses and pools.
- Three out of four (74 percent) Americans agree, ‘the growth of the solar water heating industry will produce jobs and help the American economy.’ This support is strong across regions of the country and across party lines.
Basics of Solar Water Heating Technology
Solar water heating systems can be installed on most homes in the U.S., and are comprised of three main elements: the solar collector, insulated piping, and a hot water storage tank. Electronic controls can also be included, as well as a freeze protection system for colder climates. The solar collector gathers the heat from solar radiation and transfers the heat to potable water. This heated water flows out of the collector to a hot water tank, and is used as necessary. Auxiliary heating can remain connected to the hot water tank for back‐up if necessary.
In colder climates with the possibility of freezing temperatures, an indirect system is used. An antifreeze solution, such as non-toxic propylene glycol, is heated in the solar collector and circulated to the hot water storage tank via a heat exchanger. The potable water in the storage tank is warmed by the hot, antifreeze‐filled heat exchanger, and the heated water can then be used as necessary, while the cooled glycol is piped back to the solar collector to be heated again.
Another common type of solar water heating system design for cold climates is called “drainback.” This type of solar energy system typically uses water as the heat transfer fluid, and is designed to allow all of the water in the solar collector to “drain back” to a holding tank in a heated portion of the building it is used on. When no sunlight is available for heating, the solar pump turns off and the water flows into the drainback tank by means of gravity.
No matter which type of solar energy system is employed, a properly designed and installed soalr water heating system can be expected to provide a significant percentage (40 to 80 percent) of a building's hot water needs.
How Solar Water Heating Collectors Work
Solar water heating collectors produce heat energy, distinguishing them from photovoltaic (PV) modules which produce electricity. There are several types of collectors: flat plate, evacuated tube, Integral Collector Storage (ICS), thermosiphon, and concentrating. Flat plate collectors are the most common type of collector in the U.S.; copper pipes are affixed to an absorber plate contained in an insulated box that is covered with a tempered glass or polymer coverplate.
Evacuated tube collectors consist of rows of parallel, transparent glass tubes that have been “evacuated” of air, creating a highly efficient heat insulator for the fluid that runs inside the length of the tube. Evacuated tube systems are generally used when higher temperatures or higher volumes of water are needed, as well as for process heating and solar air conditioning systems.