Solar Water Heaters

Fact: Water heating uses 14% of the energy in U.S. homes. When buying a new water heater or upgrading what you have, consider a solar water heater. Using sunshine to heat your water is free, environmentally friendly, and cost competitive in many applications when you account for the total energy costs over the life of the system. You can:

  • Save as much as 50-85% annually on the water heating portion of your utility bill (as compared to electric water heaters).

  • Help utilities avoid producing more than 50 tons of carbon dioxide (greenhouse gas).

Best Features: Solar water heaters are made up of collectors, storage tanks and, if it is an active system (vs. passive), an electric pump to circulate the heat transfer fluid. Most systems use a roof-mounted solar collector, so you will need a south-facing roof with good solar exposure. A typical solar water heating system circulates water or an antifreeze solution through this solar collector where the sun's heat warms the liquid. Take the same care in choosing a solar water heater that you would in purchasing any major appliance.

  • Your best protection is to choose only certified and labeled systems.

  • Choose water if you want the system to circulate between the solar collector and a storage tank in your house, with the latter serving as your hot water source.

  • Select a model with an antifreeze solution if you want the system to circulate it between the collectors and your storage tank, but prefer to get your hot water through multiple water tanks.

Save Money: Water heating is the third largest energy expense in U.S. households. If your water heater is more than 10 years old, its efficiency is probably no higher than 50%. An old water heater can operate for years at very low efficiencies before it finally fails. Replacing this old unit with a solar water heater could save you up to 85% on the heating portion of your utility bill. Check to see if there are any rebate or special financing options available. Here are some tips to help you save money:

  • Buy appliances with low water usage, such as front-loading washing machines and Energy Star® dishwashers.

  • Install water-conserving plumbing fixtures.

  • Insulate the tank and hot water pipes.

  • Lower the thermostat on your water heater to 120°F.

  • Install a heat trap above the water heater to minimize standby losses.

  • Drain a quart of water from your hot water tank every three months to remove sediment that prevents heat transfer and lowers the unit's efficiency.


Find It: A solar water heater is a long-term investment that will save you money and energy for many years. Like other renewable energy systems, solar water heaters minimize the environmental effects of enjoying a comfortable, modern lifestyle. In addition, they provide insurance against energy price increases, help reduce our dependence on foreign oil, and are investments in everyone's future.

You can use the sun's heat to provide your home with hot water, including basic information on the types of systems available and their economic and environmental benefits. Solar water heaters, sometimes called solar domestic hot water systems, may be a good investment for you and your family. Solar water heaters are cost competitive in many applications when you account for the total energy costs over the life of the system. Although the initial cost of solar water heaters is higher than that of conventional water heaters, the fuel (sunshine) is free. Plus, they are environmentally friendly. To take advantage of these heaters, you must have an unshaded, south-facing location (a roof, for example) on your property.

These systems use the sun to heat either water or a heat-transfer fluid, such as a water-glycol antifreeze mixture, in collectors generally mounted on a roof. The heated water is then stored in a tank similar to a conventional gas or electric water tank. Some systems use an electric pump to circulate the fluid through the collectors. Solar Water Heating

Solar water heaters can operate in any climate. Performance varies depending, in part, on how much solar energy is available at the site, but also on how cold the water coming into the system is. The colder the water, the more efficiently the system operates. In almost all climates, you will need a conventional backup system. In fact, many building codes require a conventional water heater as the backup.

First Things First: Local zoning laws or covenants may restrict where you can place your collectors. Check with your city, county, and homeowners association to find out about any restrictions. Before investing in any solar energy system, it is more cost effective to invest in making your home more energy efficient. Taking steps to use less hot water and to lower the temperature of the hot water you use reduces the size and cost of your solar water heater.

Good first steps are installing low-flow showerheads or flow restrictors in shower heads and faucets, insulating your current water heater, and insulating any hot water pipes that pass through unheated areas. If you have no dishwasher, or your dishwasher is equipped with its own automatic water heater, lower the thermostat on your water heater to 120°F (49°C). For more information on ways to use less energy for water heating, see Energy efficient Water Heating.

You'll also want to make sure your site has enough available sunshine to meet your needs efficiently and economically. Your local solar equipment dealer can perform a solar site analysis for you or show you how to do your own. See section Assessing Climate To Improve Solar Design.

Solar Water Heater Basics: Solar water heaters are made up of collectors, storage tanks, and, depending on the system, electric pumps. There are basically three types of collectors: flat-plate, evacuated-tube, and concentrating. A flat-plate collector, the most common type, is an insulated, weather-proofed box containing a dark absorber plate under one or more transparent or translucent covers.

Evacuated-tube collectors are made up of rows of parallel, transparent glass tubes. Each tube consists of a glass outer tube and an inner tube, or absorber, covered with a selective coating that absorbs solar energy well but inhibits radiative heat loss. The air is withdrawn ( "evacuated") from the space between the tubes to form a vacuum, which eliminates conductive and convective heat loss.

Concentrating collectors for residential applications are usually parabolic troughs that use mirrored surfaces to concentrate the sun's energy on an absorber tube (called a receiver) containing a heat-transfer fluid. See section Residential Solar Heating Collectors.

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