Hi,
I have come up with a design for a cheap solar thermal collector. I have posted it on this site:-
http://openfarmtech.org/forum/discussion/196/a-two-lens-design-for-a-cheap-solar-thermal-collectorThe system shown in the first attached diagram can be used as a concentrating solar thermal system. The object is to achieve a concentration ration of 100:1 to run a stirling engine using as little expensive materials as possible.
• It uses a transparent plastic or glass spherical container that act like a spot lens when filled with water. The lens focuses a large amount of sunlight at its focus.
• The focus of this lens would be a small spot, just like a parabolic dish. We have to place another small spherical water lens controlled by a microprocessor close to this focus.
• The combination of a large and a small spherical lens would be used to focus light at a single spot. The effective concentration ratio would be very large.
• Since the focus lies below the lens, one needs to take care that the lens is placed at a sufficient elevation so that there is enough room for the small lens and the striling engine to move throughout the day and still focus light on the engine.
• This system acts as a cheaper alternative to expensive dish-sterling systems.
The weight of the larger lens could be a concern, since it is a large sphere filled with water. In order to reduce the weight, the following design shown in the second diagram can be used.
Two concentric transparent spheres with water filled in the space between them can be used as a lens. It will significantly reduce the weight.
Advantages of the lens collector over the Dish Collector:-
• It eliminates the need for a reflective glass surface completely. The highly reflective glasses used in the contemporary designs are very expensive and represent a significant part of the development cost. This design could bring down the cost significantly.
• In the Dish collector, it is required that the entire dish has to track the movement of the sun continuously. This requires giant heliostats, motors etc. But in the lens collector, only the small lens and the stirling engine has to be adjusted according to the movement of the sun. It requires cheap microprocessors and small motors that can be programmed easily.
• The round shape of the lens and its weight provide better protection against strong winds than the large dish shape.
• The lenses can be filled with sea water, since it is not corrosive to plastic. So a vast unutilized resource can be used to generate electricity. There is no need to use fresh water for this purpose.