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Solar Water Heaters

Systems that use the sun to heat either water or a heat-transfer fluid in collectors generally mounted on a roof

Roof-mounted solar water heater collects heat from the sun

Harnessing energy from the sun to heat water is nothing new. Solar water heaters have been commercially available since the 1800s. What's new is how solar water heaters look these days. Most modern solar water heaters mount flush with a home's roof and resemble skylights. Solar water heaters are an environmentally sound way to reduce energy bills.

Solar energy can meet part or all of a home's domestic hot water needs. Geographic location, system design, collector orientation, and collector size will determine how much energy can be provided for domestic hot water heating.

Solar water heaters come in a variety of configurations. Each differs in design, cost, performance, and level of complexity. Most systems have back-up water heating such as electricity or gas. A solar water heating system usually consists of a hot water storage tank, a solar collector that absorbs solar energy, a back-up energy source, and (for forced circulation systems) a pump and controls.

There are two main types of systems: passive and forced circulation. Within each type, there are several configurations. A passive water heater consists of a water tank integrated into or located above a solar collector. In an integrated collector storage (ICS) system, also called batch water heater, the water is heated and stored inside the collector. These systems are suitable only for warm climates where there is no risk of freezing. In a passive system where the storage is separate from the collector, as water in the collector warms, water flows by natural convection through the collector to the storage tank. A forced circulation system requires a pump to move water from the storage tank to the collector. Most solar water heaters in the United States are the forced circulation type.

There are several types of solar collectors. Most consist of a flat copper plate, painted black, that has water tubes attached to the absorber plate. As solar energy falls on the copper plate and is absorbed, the energy is transferred to water flowing in the tubes. The absorber plate is mounted in a casing that has a clear covering and insulation to protect the absorber plate from heat loss. Other collectors include an integrated collector and storage system and the evacuated tube collector. Integral collector and storage systems combine the function of hot water storage and solar energy collection into one unit. Evacuated tube collectors produce higher temperature water and are more complex than flat plate collectors. Evacuated tube collectors consist of a series of tubes that contain a heat pipe to absorb solar energy and transfer it to a liquid medium. The tubes are evacuated (vacuum) so that there is very little heat loss from the tube. Most solar collectors are roof-mounted. Solar water heaters are used for domestic hot water, pool heating and space heating needs.


Energy Efficiency

Solar water heaters can help save on water heating costs by reducing the amount of gas and electricity needed to heat water.

Environmental Performance

By using sunlight to heat water instead of a combustible source or power plant-produced electricity, less pollutants are being introduced into the environment.


Not-so-easy

There are a number of manufacturers of solar water heating systems. Manufacturers can provide information on local dealers and installers. The Solar Rating and Certification Corporation (http://www.solar-rating.org/) provides evaluations of solar collectors and solar hot water systems. The evaluation includes an estimate of the performance of different systems based on the location where the system will be used.

Solar water heating systems may require periodic maintenance and have a relatively high initial cost. The payback period however is different depending on the cost of energy for heating water. In areas where electricity is used for water heating, the payback periods are shorter than for areas that use natural gas for water heating. Care must be taken to guard against freezing of the collector and piping. Solar collectors may have installation limits some communities.


An active, flat plate solar collector system will cost approximately $2,500 to $3,500 installed and produce about 80 to 100 gallons of hot water per day. A passive system will cost about $1,000 to $2,000 installed but will have a lower capacity.


Solar water heaters can save energy costs significantly depending on the climate and system.


Check local building codes to determine codes related to the installation of solar water heaters. The Solar Ratings and Certification Corporation runs a certification program for solar water heating systems.


John Wesley Miller Companies: Armory Park del Sol, Tucson, Arizona

Shea Homes: San Diego, California


An experienced contractor should install solar water heating systems. Usually, a roof penetration is required.


Warranties range from 3 to 10 years, varying on manufacturer.


Solar water heaters save energy and use a renewable resource. By replacing electric energy or fossil fuel use for water heating, environmental carbon emissions associated with water heating are reduced or eliminated. A solar water heating system may result in immediate positive cash flow if the monthly cost of financing the system is less than the net savings. Some states have an incentive program to support the cost of installing renewable energy systems. Check at Database of State Incentives for Renewable Energy (DSIRE) for a listing of these incentives.

Disclaimer: The information on the system, product or material presented herein is provided for informational purposes only. The technical descriptions, details, requirements, and limitations expressed do not constitute an endorsement, approval, or acceptance of the subject matter by the NAHB Research Center. There are no warranties, either expressed or implied, regarding the accuracy or completeness of this information. Full reproduction, without modification, is permissible.