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Applications of Solar Thermal Technology
By Adrian Greetham

Solar thermal technology has a variety of domestic, commercial and industrial applications. They range in scale from simple cooking techniques, to large scale industrial power generation.

Cooking

There are two main types of solar thermal cooking technologies, direct solar concentrators and solar ovens.

Direct solar concentrators

Direct solar concentrators use reflectors to focus the suns rays onto a cooking container, achieving temperatures as high as 350°C. The reflectors used vary in design, with disc, flat plate and parabolic trough the most common types. They all require direct sunlight to operate and thus are most commonly used in countries where overcast days are rare.

Solar ovens

Solar ovens basically comprise of an insulated, internally reflective box with a transparent lid. Pots are placed within the box and can be heated to temperatures between 50 and 100°C. Although the temperatures are significantly lower than those achieved using direct solar concentrators, this system does have the advantage of being able to operate on overcast days.

Water heating

Domestic water heating is the most common use of solar thermal energy. In these systems solar energy is collected via solar panels and used to provide a significant portion of the total energy requirement for water heating within a home. This results in dramatically reduced conventional energy bills, particularly during the summer months.

These systems operate by either heating water directly within the solar collectors or by heating a transfer fluid that is then used to heat water via a heat exchange system. The water is moved from the collectors to a water tank either passively using thermodynamics or actively with an electric pump system.

There are two main types of solar collector, flat panel and vacuum tube. Flat panel collectors are cheap but inefficient whereas vacuum tube based collectors are more efficient but more costly.

Room heating, cooling and ventilation

Solar thermal technology can be used for both heating and ventilating rooms.

Room heating

Room heating is achieved by using materials of high thermal mass such as concrete, water or stone to store solar energy during the day, which can then be released when room temperatures drop.

Room cooling

It may seem odd that the suns heat can be used to actually cool air spaces but it is in fact true. There are multiple methods of solar air cooling one example being an absorption refrigerator. This works by using a source of heat (the sun) to drive a cooling system.

Ventilation

One example of a solar thermal ventilation system is the solar chimney. Solar chimneys use solar energy to heat air within them causing an up draft and therefore circulating air throughout a building.

Power generation

Solar energy can be used to generate electricity. This is achieved by using solar energy to drive steam or gas turbines. To reach the extreme temperatures required for efficient conversion to electricity, solar radiation must be concentrated by lenses or mirrors. This is known as concentrated solar power. As the sun moves throughout the day the lenses or mirrors used to concentrate the sunlight must also move to ensure that the solar radiation is focused in the correct position.

There are a variety of methods for concentrating the suns radiation and tracking the sun:

Solar towers

These consist of a central tower which houses a receiver for the solar radiation and an array of flat mirrors that reflect sun light onto the receiver. The mirrors are movable so that they can track the sun to maintain focus upon the receiver.

Parabolic trough

This is a curved reflective trough which reflects sunlight onto a pipe which contains a heat transfer fluid. The pipe is positioned above the reflectors and runs parallel to them. The trough can be tilted so that it can follow the position of the sun and maintain the focus of the suns radiation on the pipe. This design is less efficient than the solar tower system described above as the temperatures reached are lower.

Dishes

Dish systems use a large, reflective dish to focus light on a receiver that is positioned above the dish. The parabolic dish is movable so that it can track the suns position and maintain optimal focus.

Solar Energy Solution install solar panels for solar water heating across the UK.

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