C-band dish solar furnace

C-band dish solar furnace
Canning Tomatoes with the sun

Back in the 60's I was given a nice rugged parabolic dish, and had covered it with mirrors. It works pretty well. I have reached aluminum melting temperatures, and run a steam engine.
Old radar dishes are not readily available but old C band dishes are.
Start with an old C-band satellite dish. Cut Bathroom mirror tile into 2" or 3" inch squares.
Glue tiles to dish with silicone rubber,then glue aluminum foil to the back with a thin coating of silicone to seal out moisture, and protect the mirrors back.The small gap between the mirrors will allow eventual total curing of the silicone, but it takes several months for a full cure. The layer of aluminum foil stops the degradation of the mirrors rear surfaces. My dish has been outdoors for over 30 years and the mirrors are still like new.
The horizontal and vertical drives are run by a sun tracking servo amp that keeps it pointed at the sun.
A schematic of the basic tracker is available on the downloads page:Simple Tracker schematic
This generic servo will operate on 12-24VDC, and will run dc motors over the same voltage range. The power transistors need to be mounted on a good heatsink with electrical isolation between the collectors and the heatsink. The servo gain pot will want to be tuned for best accuracy of tracking without oscillation.
The sensing photo detectors are mounted at + and - 45 degrees to form a half bridge.The + of one detector connecting to the - of the other. This "shorted" connection forms a current bridge where the two photo diode currents cancel when evenly illuminated, and change polarity and amplitude of output when unbalanced. The idea is to have the servo always drive the dish to the null point.
I Canned some tomatoes this morning. The 8 quarts of water and tomatoes reached boiling in 6 minutes, but then it was boiling too fast. I had to drape news papers over the mirrors to turn down the heat. I will need to make an adjustable shade for the thing, so I can adjust the boil to a slow steady one. Tracker worked well.I need a steam engine for the thing, and I could make some electricity or pump water.
More information on this project:
Plugging into the sun blog