SUN SOLUTIONS

Solar Water Heating

Background
Though civilizations have long sought to capture the sun's rays for uses ranging from weapons to cooking, the first solar water heating collector appears to have been built in the 18th Century by a Swiss scientist named Horace Benedict de Saussure. It was simply a wooden box with a glass top and a black base. By trapping solar energy, the collector reached a temperature of 190 degrees Fahrenheit.

 The U.S. solar water and space heating industry currently incorporates approximately 30 companies involved in the manufacturing of solar collectors and generate $65 million in annual sales. Today, more than one million homes in our country alone use state-of-the-art solar equipment to heat water for household use, and over three hundred thousand families use simple solar collectors to heat the water in their swimming pools. Solar collectors are a common sight on homes and buildings throughout much of the developed world, and many Third World countries use simple solar collectors as their only source of hot water.

The Technology
Solar energy refers to the use of the sun's rays rather than electricity, oil, kerosene or natural gas to provide heat for a wide variety of uses. Solar thermal systems collect the sun's heat and either direct it for use (such as heating water or producing steam for power), or store it for later use. Recent scientific and engineering advances, coupled with dramatic improvements in the quality of materials and design, have made the United States a world leader in the development and application of solar heat technologies.

 The main component of a solar system is the collector, which absorbs the radiant energy of the sun and changes it into heat energy. Most solar domestic hot water systems use flat-plate collectors. These collectors are typically mounted on the roof of a building, usually oriented due south, though they can also be ground-mounted. One or two collectors are used in typical systems, depending on the climate and the amount of demand for hot water.

 The other major part of the system is a storage tank. Though conventional electric tanks can be modified for solar service, specially designed, sized and super-insulated solar tanks are available. The tanks should be large enough to provide one day's hot water demand--approximately 20 gallons per day per adult and 15 gallons per day per child.

 During cloudy weather and periods of excessive hot-water use, backup heating can be used. An electric element, located in the upper portion of a solar tank or in a converted electric heater, will come on when the collectors are not providing enough hot water.

Types of Systems
There are several different types of flat-plate collectors used in solar water heating systems. In general, they fall into one of three categories:

Active Systems use a pump to circulate the water or other fluid from the collector, where it is heated by the sun, to the storage tank, where the water is kept hot until is needed.

 Integral Collector Systems (ICS), also called "batch" or "breadbox" water heaters, combine the collector and the storage tank into one. The sun shining on the collector strikes the storage tank directly, heating the water.

 Thermosyphon Systems use a separate storage tank located above the collector. Liquid warmed in the collector rises naturally to the tank where it is kept until needed. A major benefit of these systems is that they require no moving parts.

As part of the above systems, an FDA-approved antifreeze is often utilized in areas where the temperature falls below freezing in the winter. These systems drain the collectors or recirculate warm water through them in freezing weather.

 The ICS and thermosyphon systems are often called "passive" solar water heaters because they do not use pumps to move the heater water. All three types of solar systems work well.

 Other types of solar collectors are used for different purposes. For example, unglazed flat-plate liquid collectors are usually used for swimming pool heating. Air-type collectors are used for space heating, allowing the sun to heat the air in the collectors. The air is then vented into the home by a fan.

Economics
Solar water heaters can be more economical over the life of the system than heating water with electricity, fuel oil or propane gas. In sunbelt states, solar systems can easily provide faster paybacks and rates of return on investment of 10 or 11 percent or more. Just about every part of the country will find solar systems paying for themselves during the system's lifetime.

 Savings are even greater in new construction, where builders can install solar equipment without having to first purchase conventional water heating equipment, thus saving on both installation costs and some of the equipment costs "up-front."

 The cost of a solar system varies widely, depending upon the materials of the various components and services offered by the seller. Currently, average prices for an installed, active-solar system range from $2,500 to $3,500 for a single family home with four occupants. Compared with the cost of a conventional electric, fuel oil or gas heater, this represents a significantly higher initial investment.

 However, to make an accurate economic comparison, the cost of the fuel for a conventional heater over its lifetime must also be considered. For example, a solar system might cost $3,000 with the local utility offering a $300 rebate (many utility companies around the United States offer incentives to customers purchasing solar equipment). Because nearly half of the states have a state tax credit for solar equipment, assume that the credit in your state gives another $600 deduction. The total system cost is thus $2,100. Based on recent energy costs, a family of four might save an average of $40 per month, or $480 per year on water heating costs. Their savings will pay back the cost of the system in about 4-1/2 years. Considering that the systems last approximately 20 years, the savings over the remaining 15-1/2 years would be cash in the pocket. Future increases in utility rates would make the savings with solar even bigger.

The Sun Solutions brochure also contains information on solar pool heating, solar electricity, solar thermal power, passive solar energy and energy conservation. If you'd like to view the entire document,click here.

This document was developed by:

Solar Energy Research and Education Foundation
Solar Energy Industries Association
1616 H Street NW, #800
Washington, DC 20006
Phone: (202) 628 - 7745
Fax: (202) 628 - 7779