Solarbuzz is concerned mostly with solar photovoltaics - the direct conversion of sunlight to electricity. However, there are other important applications of solar energy relating to solar generation of heat, referred to as "solar thermal".

In the simplest solar thermal application, a discrete solar collector gathers solar radiation to heat air or water for domestic, commercial or industrial use. The solar panel is usually a flat plate collector that consists of a metal box with a glass or plastic cover and a black absorber plate at the bottom.

Absorber plates are usually painted with selective coatings that absorb and retain heat better than ordinary black paint. They are normally made of metal, typically copper or aluminium, because it is a good conductor of heat. Copper is more expensive, but it is a better conductor and is less prone to corrosion than aluminium. The sides and bottom of the collector are usually insulated to minimize heat loss.

In locations with average available solar energy, flat plate collectors are sized at approximately 0.5 to 1 square foot per gallon of daily hot water use. Evacuated tube collectors have absorber plates that are metal strips running down the center of each tube.

Convective heat losses are reduced by virtue of the vacuum in the tube. For swimming pool heating, plastic or rubber are used to make low-temperature absorber plates.

The solar collector is usually mounted on the roof and is connected to a circuit containing water with propylene glycol anti-freeze added, if necessary. The heated liquid flows around the circuit, either under the action of a pump to warm the main hot water tank, or by a thermo-syphoning action to warm a solar water storage tank that then feeds the hot water tank.

Pool systems pump the water directly through the solar collectors. Because water in the pool is usually kept at about 80°F, collectors for pool heating systems may not have glazing or insulation.

They also do not need to be protected against freezing because swimming pools are generally used only in warm weather or can be drained easily when it's cold.

Passive solar heating is the absorption of solar energy in a building to reduce the energy required to warm the habitable areas (i.e. to contribute to space heating).

Air is normally used to circulate and distribute the collected energy, generally without the use of pumps or fans. The collector may be an integral part of the building, perhaps designed as part of an architectural feature that provides light and heat.

Indeed, the air flow generated can be used as a means of ventilating the building, or even cooling it by drawing in cooler air to replace upwardly moving solar heated air.

Search our Companies by Country and Region to find the solar thermal company nearest you.

In solar hot water systems, sunlight reduces the amount of electricity or gas required to heat your hot water supply, so it cuts your fuel bills. Residential buildings benefit most where hot water demand is highest e.g. a large family or a big laundry load.

Commercial or industrial solar water heating systems are most cost effective in facilities with water heating systems that are expensive to operate, or in operations such as laundries or kitchens that require large quantities of hot water. Solar thermal space heating may advantageous in off-grid buildings, or in cases where the grid electricity supply is unreliable.

According to the Federal Energy Management Program Solar Water Heating Technology Alert, flat plate water heating systems range in price from about $2,000 to $4,000 installed for residential systems (for 40 to 80 gallons per day usage), and $2,000 to $50,000 for commercial systems (for 40 to 1700 gallons per day usage). Their chart below compares the percentage of water heating energy that solar can provide in various cities for a 48 square-foot flat plate solar hot water system based on average water usage for four persons.

Source: http://www.pnl.gov/techguide/16.htm

Solar thermal energy can be collected at large scale and used to heat a transfer fluid that can then power a steam turbine to generate electricity. Sunlight may be collected using huge mirror arrays focussed on to a receiver at the top of a tower or, at the other extreme, may be based on the temperature gradient produced when sunlight impinges on a "solar pond" (a large salty lake) and heats the water at its base.

Most commercially attractive is the solar thermal electricity generation system originally developed by Luz, which uses parabolic reflectors to warm a heat-transfer oil running through a pipe at the focus of the reflector. This heated oil is used to raise steam to power a turbine.