Today testing a Compound Parabolic Concentrator of Solar Energy

Dear Fellow Public Inventors,

I apologize for not posting more.  Although this blog has been silent, I have in fact been making excellent progress.  As you may recall I have joined ATX Hackerspace here in Austin.  In addition to a space and some valuable tools, such as a CNC laser, cutters, they have a wonderful community of brilliant hackers.

As I mentioned previously, I have mothballed the Merfluke, and have begun working on a Solar Cooker, a preliminary design of which was posted in the blog.

I'm very happy to have formed a friendly partnership with Elliot Hallmark, who is interested in solar power and very knowledgeable about the mathematics of them.  Also, he knows how to use the laser cutter, a really fabulous Tom-Swift type tool capable of cutting 1/4" inch hardwood plywood.  Below you can find some snapshots of our current design, which Elliot cut from plywood with the laser cutter.

This shape is the famous "Compound Parabolic Concentrator" pioneered by Roland Winston.  The entrance pupil is 1 foot square (144 square inches), and the exit pupil is 3" square (9 square inches).  If we have perfect reflectance, this should provide a flux concentration of 16 suns!  That is, it should be as if 16 suns were shining on the exit pupil.  This should in theory be enough to cook something.

I have cut the reflectors out of sheet aluminum.  It is unclear to us if this will be an adequate reflector or not.

Elliot and I seem to be harmoniously agreeing to use "Agile" development processes.  I personally give my hero Kent Beck credit for a lot of this, but Wikispeed and others are apparently using the same ideas.

Kent's motto is "Do the simplest thing that can possibly work."  Elliot and I are trying to do that.  We are know of course that 1 square foot of sunlight won't let you cook more than a hard-boiled egg, but we are starting with a miniature model before we build the full-on West Texas hog roast model!

We so far have identified 3 modules that we can change independently: the reflector panels, the CPC (pictured here in plywood with paper panels) and the oven box, which mates to the CPC via a 3"x3" square aperture.  Kent's approach to going fast is to "take baby steps as fast as you can".  These three modules allow us to independently improve our reflectance, our collector, and our oven.

Our oven is a cardboard box with a meat thermometer jammed into it.  Today is a mostly sunny day in Austin.  Our hope is to glue the other 3 aluminum panels in place (we're using hot melt glue for now) and see if 1) we can get anywhere close to 16 suns of brightness (I'd settle for 8!) and 2) can we reach a stagnation temperature of 200 or 300 degrees F in the cardboard box.

Note that a big part of what I proposed was vandal-proofing and convenience, and we aren't addressing those things yet, because until we can cook an egg there is no point in it.

Finally, let me say: you are all invited to help!  Elliot and I make a great team, I think---I'm providing the funding, and the metal-working skill, and Elliot has done the math and cut the wood, but there is plenty of room for others to contribute.  In particular, we will, if successful, eventually need an artist to help us make it attractive, a microprocessor guy to build the temperature monitoring, mechanical engineers to make a smoothly and safely operating oven that food an be taken in and out of, and test chefs!  So don't be shy---send me email and work together with us!