What is a Parabolic Solar Concentrator? What is a Parabolic Solar Concentrator?

A parabolic solar concentrator is a curved set of mirrors which focus all incident sunlight onto a single point. These concentrators are used to greatly increase the intensity of sunlight. The concentrated sunlight generates such extreme amounts of heat that it is dangerous. A parabolic solar collector can burn the operator if safety procedures are not followed. These concentrators have a variety of uses. Two of the main uses are solar cooking and concentrated solar power. Solar cooking uses relatively small-scale parabolic reflectors to focus sunlight on water or food. Concentrated solar power uses relatively large-scale reflectors to boil water. The pressure of the steam rotates a turbine, generating alternating-current electricity. This process is more efficient than generating direct current electricity in photovoltaic cells.

Principles

A parabola is a symmetric 2-dimensional curve. It is represented mathematically by the equation y=x^2. Parabolic concentrators are 3-dimensional, but curved in the same manner along their length and width. The concentrators are lined with mirrors or covered with a reflective coating such as mylar or aluminum foil. Of course, using liners with higher reflectivity results in more powerful solar concentrators. When light strikes a reflective surface, it bounces off at the same angle. The parabolic concentrator is curved so that all the light reflects to a single point, regardless of where it strikes the surface of the concentrator. For this reason, increasing the surface area of the concentrator increases its power. The distance between the surface of the concentrator and the point where light concentrates is the focal length. In a shallow parabola, the focus is outside of the reflector rim. In a deep parabola, the focus is inside the reflector rim.

Solar Cooker

Parabolic solar concentrators are commonly used as solar cookers, especially in developing countries. Their suitability and portability has increased over time with gradual changes to the design. Large concentrators make poor cookers because the focal area is too small and moves too rapidly. The best parabolic solar cookers have a focal length between 3 and 9 feet. They first became popular with the 1959 Wisconsin design, a portable solar cooker that could boil 1 liter of water in 20 minutes. Newer collapsible parabolic cookers strongly resemble umbrellas. They are highly portable, making them ideal for camping trips. NGOs and researchers have also constructed large community cookers in cities, towns, and rural villages throughout Asia.

Concentrated Solar Power

In addition to small scale domestic uses, solar concentrators are also used for industrial purposes. Large scale concentrators boil water into steam for heating and industrial processes. The steam can also spin turbines to generate electricity. In a concentrated solar thermal plant, the parabolic reflectors focus the sun's energy onto a length of pipe suspended in the focal point. The pipe may contain water or molten salt. These reflectors are very large and have to cleaned regularly with detergent, deionized water, and a rinsing agent. Large solar farms can take up acres, they are usually located in remote undeveloped parts of arid regions.

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