Heating

Solar Thermal

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

Solar Collectors

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 to absorb and retain heat better than ordinary black paint. Absorber plates are normally made of metal, typically copper or aluminum. The sides and bottom of the collector may be insulated to minimize heat loss.

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

Passive Solar Heating

Passive solar heating is the absorption of solar energy in a building which reduces the energy required to warm the habitable areas. This contributes 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. 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.

In solar hot water systems, sunlight reduces the amount of electricity or gas required to heat a hot water supply, thereby reducing fuel costs. Commercial or industrial solar water heating systems are most cost effective in facilities with water heating systems, such as laundries or kitchens, which require large quantities of hot water. Solar thermal space heating may be advantageous in off-grid buildings or where the grid electricity supply is unreliable.

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Power Generation

Electricity Generation

Solar thermal energy can be collected on a large scale and used to heat a transfer fluid. This fluid can then power a steam turbine that generates electricity. Sunlight may be collected using huge mirror arrays focused on a receiver at the top of a tower. At the opposite extreme, it 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.

The solar thermal electricity generation system is the most commercially attractive. This system uses parabolic reflectors to warm 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.

Applications

Lighting

Concept of Operation

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