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Solar Devices: Low Cost, Large, Variable Focus Solar Concentrator

Client

UROP Program at the Mechanical Engineering Department, M.I.T.

Problem

One of the major problems associated with the use of solar energy is the cost of collectors. In the case of concentrator collectors the problem is even more serious. Besides that, variable focus solar concentrators do not exist. An attempt was made here to produce a concentrator of low cost and reasonably good optical characteristics.

Solution

For most applications where ideal optical characteristics are not essential, a rigid solid surface is hardly justifiable economically. In those cases reflecting films are more attractive. The only problem remaining is the cost of the frame. In the case of a concentrator mirror, the advantages of such a surface could justify the frame cost.

The concept of this film concentrator could not be simpler. A film of reflecting Mylar was attached to a steel dish of flat circular rim although not necessarily well made otherwise. The whole system was well sealed and in between was evacuated with a small vacuum pump. The surface of the taut Mylar film was depressed in a reasonably good optical shape. Only the boundaries showed imperfections. No focal temperatures were measured, but on a clear day wood would burn at the focus almost instantly. The focus could easily be varied by merely changing the pressure differential across the film surface. there may be some applications for this simple approach.

Picture of the Low Cost, Large, Variable Focus Solar Concentrator