Solar water heaters can be used to heat swimming pools and spas.

In a solar pool-heating system, the existing pool filtration system pumps pool water through the solar collector, and the collected heat is transferred directly to the pool water. Solar pool-heating collectors operate just slightly warmer than the surrounding air temperature and typically use inexpensive, unglazed, low-temperature collectors made from specially formulated plastic materials. Glazed (glass-covered) solar collectors are not typically used in pool-heating applications, except for indoor pools, hot tubs, or spas in colder climates. In some cases, unglazed copper or copper-aluminum solar collectors are used.

In residential applications where the goal is usually to extend the swimming season into spring and fall, heating a swimming pool with solar energy requires a solar collector that is 50% to 100% of the surface area of the pool. In general, adding more square footage lengthens the swimming season and allows owners to use the pool in colder weather. A pool cover or blanket significantly reduces heat loss in a cost-effective manner and helps maintain warm temperatures for long periods.

A solar pool-heating system costs between $2,000 and $10,000 to buy and install, depending on size. Costs run between $7 – $12 per square foot depending on system design and collection type. This provides a return on investment between 1.5 and 7 years, depending on the cost of the auxiliary energy being displaced.

Maintenance of solar pool-heating systems is minimal. The systems are pre-engineered and can be sized for any pool by simply adding additional solar panels to obtain an adequate solar collector area.

The only moving part on a solar pool-heating system is the diverting valve. This valve controls when the water circulates through the collector loop. If the collector temperature is sufficiently higher than the temperature of the water in the pool, water is diverted from the filter systems through the collector loop. The water bypasses the solar collectors during the night or cloudy periods. Some smaller systems are operated manually or with timers. Larger systems are operated by electronic sensors and controls.

Here’s a look at some things we can expect in the future from solar technologies.

All our buildings will feature energy-efficient design, construction, and materials as well as renewable energy technologies. In effect, each building will both conserve energy and produce its own supply, to be one of a new generation of cost-effective “zero-energy buildings” that have no net annual need for nonrenewable energy.

In photovoltaic research and development, there will be more breakthroughs in new materials, cell designs, and novel approaches to product development. In a solar future, your mode of transportation—and even the clothes you wear—could produce clean, safe electric power.

With today’s technology roadmaps to lead the way, concentrating solar power will be fully competitive with conventional power-generating technologies within a decade. Concentrating solar power, or solar thermal electricity, could harness enough of the sun’s energy to provide large-scale, domestically secure, and environmentally friendly electricity, especially in the southwestern United States.

The enormous solar power potential of the Southwest—comparable in scale to the huge hydropower resource of the Northwest—will be realized. A desert area 10 miles by 15 miles could provide 20,000 megawatts of power, and the electricity needs of the entire United States could theoretically be met by a photovoltaic array within an area 100 miles on a side.

Within 10 years, photovoltaic power will be competitive in price with traditional sources of electricity.

Solar electricity will be used in an electrolysis process that separates the hydrogen and oxygen in water so the hydrogen can be used in fuel cells for transportation and in buildings.

Just as solar energy can heat the water for a building, it can also heat and cool the air.

Space Heating

A solar space-heating system can consist of a passive system, an active system, or a combination of both. Passive systems are typically less costly and less complex than active systems. However, when retrofitting a building, active systems might be the only option for obtaining solar energy.

Passive Solar Space Heating

Passive solar space heating takes advantage of warmth from the sun through design features, such as large south-facing windows, and materials in the floors or walls that absorb warmth during the day and release that warmth at night when it is needed most. A sunspace or greenhouse is a good example of a passive system for solar space heating.

Passive solar design systems usually have one of three designs:

• Direct gain (the simplest system) stores and slowly releases heat energy collected from the sun shining directly into the building and warming materials such as tile or concrete. Care must be taken to avoid overheating the space.
• Indirect gain (similar to direct gain) uses materials that hold, store, and release heat; the material is located between the sun and living space (typically the wall).
• Isolated gain collects solar energy remote from the location of the primary living area. For example, a sunroom attached to a house collects warmer air that flows naturally to the rest of the house.

For more information about passive solar space heating, visit the EERE Passive Solar Heating, Cooling, and Daylighting page.

Active Solar Space Heating

Active solar space-heating systems consist of collectors that collect and absorb solar radiation combined with electric fans or pumps to transfer and distribute that solar heat. Active systems also generally have an energy-storage system to provide heat when the sun is not shining. The two basic types of active solar space-heating systems use either liquid or air as the heat-transfer medium in their solar energy collectors.

Liquid-based systems heat water or an antifreeze solution in a hydronic collector. Air-based systems heat air in an air collector. Air-based solar heating systems usually employ an air-to-water heat exchanger to supply heat to the domestic hot water system, making the system useful in the summertime. Both of these systems collect and absorb solar radiation, then transfer the solar heat directly to the interior space or to a storage system, from which the heat is distributed. An auxiliary or backup system provides heat when storage is discharged. Liquid systems are more often used when storage is included.

Here is a summary of the many different types of active solar space-heating systems:

Medium-temperature solar collectors are generally used for solar space heating. Solar space heating systems operate in much the same way as indirect solar water-heating systems, but they have a larger collector area, larger storage units, and more complex control systems. They are also usually configured to provide solar water heating and typically provide 30% to 70% of the residential heating, or combined heating and hot water, requirements. Active solar space-heating systems require more sophisticated design, installation, and maintenance techniques.

• A very economical, but specialized space heating system is based upon use of transpired air collectors, mounted as an exterior cladding on a south-facing wall. These systems are used for ventilation preheating. This system heats only outdoor air. These collectors are unglazed, and a blower or fan is used to draw air through perforations in the wall to deliver ventilation air into the building. Solar ventilation air preheating systems are generally used in commercial and industrial applications that require large quantities of ventilation air, including: a) buildings that require much outdoor ventilation, such as warehouses, large manufacturing plants, and airplane maintenance hangars; b) crop drying; and c) pre-heatingof boiler combustion air.

Space Cooling

Cooling and refrigeration can be accomplished using thermally activated cooling systems (TACS) driven by solar energy. These systems can provide year-round utilization of collected solar heat, thereby significantly increasing the cost effectiveness and energy contribution of solar installations. These systems are sized to provide 30% to 60% of building cooling requirements using solar, with the remainder usually dependent on TACS fueled by natural gas. The TACS available for solar-driven cooling include absorption systems and desiccant systems. Generally, solar cooling is not used because of the high initial costs of TACS and the solar fields needed to drive them.

• Solar absorption systems use the thermal energy from a solar collector to separate a binary mixture of an absorbent and a refrigerant fluid. The refrigerant is condensed, throttled, and evaporated to yield a cooling effect, which is then re-absorbed to continue the cycle. Double-effect absorption systems (which use the heat twice in series) are about twice as efficient as single-effect systems, but require significantly higher input temperatures. Because of the high temperature requirements of absorption cooling systems, evacuated-tube or concentrating collectors are typically used.
• Solar desiccant systems use thermal energy from the solar collector to regenerate dessicants that dry ambient air; they then use that dry air in indirect and/or direct evaporative stages to provide cooled air to the load. The solar heat is used to regenerate the desiccant, driving off the absorbed water. Some systems use flat-plate collectors at intermediate temperatures.

Thirty some years ago, just after I first started building houses, a friend (another builder) and I took on a solar hot water franchise as a side line to home building. We thought solar heating was cool and avant-garde, and that everyone else would too.

Boy, were we wrong! We couldn’t give solar heating away. People thought that the solar collectors were ugly and no one wanted those ugly contraptions on their roofs. Besides, electricity and gas were cheap, plentiful and we would never run out of either.

My, how times and thinking about things change.

Here’s the scoop from the NAHB Research Center:

“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.

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 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 $3,500installed 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.

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

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. Buy water heater with payday advance service