Reflective film is stretched over a 4' diameter dish that has a small raised surface at the face on the circumference, creating a cavity inside. A vacuum is pulled inside the dish with a small hand pump, deforming the film to a concave shape that focuses sunlight to a variable spot of intense heat. Vacuum holds for a minimum of two hours before requiring a few pumps to hold a given focus. The dish requires small adjustments as the sun moves every 5 minutes or so. Automatic tracking is planned for summer of 2017.
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