P2P Foundation

From a correspondence by Eric Hunting, these suggestions might be useful:

“Suggestions by Eric Hunting:

“Also, with your solar turbine project, are you familiar with pressure-tensioned parabolic mirrors? These have already been employed for solar stirling engines and the design is pretty simple. You basically have a rigid cylinder chamber covered in a reflective thin film mylar membrane and then use a partial vacuum in the chamber to tension the mylar and pull it into the desired parabolic shape. In some designs a clear mylar cover layer is paired with the reflective layer and rigidized with a hoop clamp frame so that increasing the pressure between the membranes can be used to tension them while the clear layer protects the reflective layer from dirt and UV. In both cases changes in ambient air pressure are compensated by using pumps to maintain consistent delta-P. I’ve only seen these used with circular parabolic reflectors but they have been made to quite enormous sizes.

See www.abetterfocus.com/files/Paper0167_stretched_Membrane_R1.pdf

Note in this paper the solution to membrane wrinkling through the use of foam battens.

Also, have you considered the use of super-saturated salt pond solar collectors? These are used both for large scale power generation with conventional municipal steam turbines at mining facilities and for small scale rooftop applications like desiccant recycling in solar-powered air conditioning. One advantage of these for the large scale facilities is that the pond can store heat energy for a long time, allowing the plants to run day and night. But such huge volumes of super-saturated salt water can’t be covered by membranes as with smaller pools and present an environmental hazard.

See www.motherearthnews.com/Modern-Homesteading/1980-05-01/Israels-150-KW-Solar-Pond.aspx

Oh, and have you seen Auroville’s solar kitchen? It’s impressiveL www.auroville.org/society/solarkitchen.htm