Last edited: 26 March 2017
A Better Focus Co., Inc. designs and manufactures concentrating solar dishes that can be used for solar cooking, water disinfection, and even steam generation. This is a long-focus dish, app. 4' in diameter, utilizing reflective film to focus to a 3-4" diameter hot spot at a distance of 10-15 feet away. Cooking surfaces (pots, pans, ovens) are mounted to a separate pole.
Theory of Operation
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.
While it is true that long focal length parabolic reflectors such as this one can cause burns or fires if the focal point is directed incorrectly, this model includes a feature in that air escapes slowly from the disk causing it to lose its parabolic shape over 1-2 hours. Its designer states that there is little danger coming in contact with the beam except within a foot or so of the focal point. The provided cover should always be placed over the dish reflective surface when not in use. A pair of sunglasses is provided with each shipment, and are strongly recommended for all observers who look at the focused light on cooking surfaces.