You can make parabolic solar heaters in either trough or disk shapes. While troughs are ideal for heating water through lengths of pipe, disk or dish parabolic heaters are effective for using the heat of the sun to heat a single item, boil a kettle of water, or cook food with the power of the sun. You can make your own solar disk heater from cardboard, paper or a thin wood veneer. You can also use an old satellite dish, as it is already in the parabolic shape needed.
Cut a piece of cardboard to a size of 10 by 10 inches to make a parabolic disk with a 1.3-inch focal length and 8-inch diameter. The focal length is the distance from the centre of the disk that will generate the most heat. You can also scale these dimensions to make a larger or smaller solar heater.
Draw three circles from the centre of the sheet using a pencil tied to a string and tacking an end of the string in the centre of the circle at 3/4 inches, 2.5 inches, 4 inches and 5.25 inches.
Draw 16 lines from the centre of the sheet using a protractor and a metal ruler, each at 22.5-degrees apart.
Cut each spoke in the circle to the centre using a pair of scissors. This will give you 16 wedge-shaped pieces. Keep them in place after you have cut them so they are still in a circle.
Begin overlapping the wedges by selecting one wedge and placing its two neighbours over the top of it so their edges touch. The seam between the two top wedges should be in the centre of the middle piece. The middle piece should be completely covered by the two top pieces.
Work around the circle, placing the next wedge below the last placed wedge. Then place the next wedge above that wedge, until every piece is either covering or is being covered by two other wedges.
Remove each top piece, paint white glue to its underside, then glue it to the two pieces below. Allow the glue to dry.
Trim off the protruding corners from the rim of the disk with scissors to make it round.
Punch a hole in each piece as close to the tip as possible using the tip of your scissors. Connect the wedges together by lining up the holes and inserting a brass paper fastener through the holes
Fan out the wedges so the edges touch, pressing them down. Tape them together using transparent packing tape on the outside of the dish. The base of your parabolic dish is now complete.
Cut a rectangle shape from a piece of aluminium foil 3 inches wide and 8 inches long using scissors and a metal ruler. (This is 3 inches longer than the radius of your dish.)
Cut the foil diagonally along the longest length, using scissors and a metal ruler, to make two wedge shaped pieces.
Mix epoxy with white glue in equal portions.
Brush the glue mixture onto the dullest side of the aluminium foil and then place it in the dish, with the point of the wedge in the centre, and the widest edge wrapped around the rim of the dish.
Prop up your dish in the sunlight using a couple pieces of 2-by-4s or other spare lumber. Then place a piece of wood in the focal point of the dish, 1.3 inches from the centre, to test the heat generated from your solar heater.
Parabolic reflectors can be dangerous. Do not construct your dish in direct sunlight. Burns or blindness could result. Never place your hand in the centre of the dish. Never leave your solar heater unattended.
Tips and warnings
- Parabolic reflectors can be dangerous. Do not construct your dish in direct sunlight. Burns or blindness could result. Never place your hand in the centre of the dish. Never leave your solar heater unattended.