A number of recent posts on this list have concerned various schemes to use solar concentrators. This is something I've been fascinated with and have played around with all my life.
I own a company that manufactures, among other things, fresnel lens arrays. Unfortunately, these have been used exclusively for rather trivial decorative purposes. Their main form has been arrays of metallized negative fresnels. This is quite attractive and results in a rather convincing and compelling 3D illusion of a shiny metal ball floating behind the surface of the substrate. You can seen the results of my work on the cover of the latest Guiness Book of World Records. There is a picture of this at: http://www.guinnessworldrecords.com/ The picture, of course, doesn't show the 3D aspect very well. (End of self-promoting commercial) The thing is, it's actually much easier to make a single large fresnel than to make these decorative arrays. What I have in mind is to make not a large single fresnel lens, but a quarter of one. The quarter sections could then be assembled on a light-weight frame into a relatively large solar concentrator. The process I use has a number of advantages over those previously implemented These lenses are made in continuous rolls, rather than pressed as individual parts. Because of a number of other innovations I am able to manufacture and sell this stuff for less than a dollar per square meter. This is roughly 1% of the cost of conventionally manufactured fresnels. Further, these are made on a high tensile strength polyester substrate, allowing thin pieces to be stretched on a frame. The stuff is so cheap it might be less expensive to replace it than to clean it. My largest machine runs film 65 inches wide, meaning four sections assembled together would give you a square 3.3 meters on a side. So you have 10.9 square meters of concentrator area capable of focusing a spot about 3cm at f1. Direct measurement of the type of fresnel I make gives about 80% of the incident sunlight delivered to the focus. Now surely someone could figure out what to do with more than 8kW of concentrated heat in a 3cm spot. The frame structure I have in mind would be a pyramid with cross bars traversing the base to support the quarter sections and the focus would be at the apex. Clearly, this type of frame could be made light-weight and relatively inexpensive. Nevertheless, the fresnel lens would be the least expensive part of the whole thing. My production capacity is really quite large and can be expanded quickly. Unlike reflective concentrators, fresnel lenses can undergo considerable flexing and disortion without seriously affecting their performance. What I would like to know, since there is such a variety of knowledgable people on this list, what would be the best use of 8kW of concentrated solar energy? Thermoelectric? Stirling? Zinc reduction? What? I really don't know what do with this, if anything. M. _______________________________________________ Join Excite! - http://www.excite.com The most personalized portal on the Web!
