I (Mike Pool) wanted to make a large solar cooker. I wanted it versatile enough to cook steaks or brown the crust on a large pizza. I started with an anodized aluminum griddle that was on a military surplus website. The griddle weighs 52 pounds and is 23 inches deep and 43 inches wide. The grill, at a comfortable working height of about 36 inches, is supported by an adjustable stand that is normally used for an electric piano or keyboard.
Four square meters of truck mirrors are used to direct sunlight to the bottom of the grill. Sixty seven West Coast truck mirrors are mounted into four frames. 1 3/4 inch square tubing that has 1/2 inch holes spaced one inch apart are used to hold the mirrors. The square tubing is 15 feet (4.5 meters) in length. To prepare each mirror for the frame, take off the hardware that comes with the mirrors. Leave a nut on one end of each mirror. Find about 3 feet of 1/4 inch, 50 psi rubber hose used for fuel lines in automobiles. Cut 1/4 inch segments out of the rubber hose and put one on each end of each mirror. The threaded rod on the mirrors will go though the holes on the square tubing. The rubber hose segments will not. The mirrors can be rotated for aiming and the friction from the rubber will hold the mirrors steady even if it is quite windy. The nut on one end of the mirrors is used to push against one of the rubber segments to adjust the amount of friction available. A 7/16 inch allthread that is 22.5 inches long goes completely through the frame. Three are used on each frame. The three pieces are spaced 4 feet apart with one in the middle of the frame. Nuts are tightened on each end of the allthread until the mirrors are snug in the frame.
The mirrors within each individual frame can be aimed to about the same focal point. Each frame needs to be tilted so that the focal points will meet at the center of the grill. This requires raising the outside rail of the two middle frames with 6 inches of 7/16 inch allthread bolted in on each end and raising the outer rail of the outside frames with a 10 inch segment bolted in. A nut is used on each allthread to make fine adjustments to the angle of the frame. The inside rails of each frame have casters on each end.
Extra spacing is used to keep the mirrors from shadowing the next mirror as you get further from the point where the mirrors lay horizontal in the frame. A space is left open on 3 of the frames for the shadow from the grill. This also allows me to get to the grill to take care of the food.
I start cooking at around 30 minutes before solar noon. I use an Omega HH11 to measure my temperature. The pictures with the pizza are from April 1, 2007. The bottom of the grill has been painted with black bbq paint. Even though the anodized grill is dark, black paint is better still for absorbing heat. With the sun at an azimuth of 178.46 degrees,and an elevation of 59.16 degrees and an ambient temperature of 19 degrees Celsius, the grill reached a temperature of 174.5 degrees Celsius (346.1 degrees Fahrenheit). This was enough to cook a 16 inch pizza in about 30 minutes.
The following is a list of materials and price that I paid:
- Anodized aluminum grill ..... $100
- Adjustable stand ..... $100
- 67 truck mirrors ..... $350
- 8 pieces of 1 3/4 inch square tubing 4.5 meters long (used)..... $24
- 1 19 inch aluminum motorcycle wheel ..... $40
- 1 Special order low iron glass. Tempered, edged smoothed 3/8 of an inch thick, (3 square foot minimum order) ..... $200
- Being able to cook without buying any fuel: PRICELESS!!!
I use glass lids to cover food when cooking on the solar grill. Glass lids will also capture the steam and speed up the cooking process. Frying flatbread and baking small rolls work great on the grill. Frozen corn is one of my favorite things to cook. The corn gets a slight roasting on the grill.I had piece of low iron glass cut to fit an aluminum motorcycle wheel. The motorcycle wheel is 19 inches in diameter. The glass is cut so that the outside edge will rest on the rim of the wheel. Low iron glass will allow more light to pass through than common float glass. The glass is tempered and 3/8 of an inch thick. The glass is used mostly to allow me to watch the cooking process since the mirrors are heating the grill anyway. The iron content gives glass a green color when looking at the edge. Low iron glass has a light green color to it when looking at the edge as can be seen on the picture below.
The spoke holes on the wheel allow moisture to escape when cooking a pizza. Other foods may benefit from holding the steam in. A piece of cloth can be wrapped around the wheel to cover the spoke holes if heat needs to be conserved. I cut a strip out of an automobile windshield reflector . I used a piece of duct tape to hold the two ends together.
When I am not using the grill, I just take the four frames and turn all of the mirrors flat. Then, I lean each frame against a back wall on the house with the mirrors facing the wall. The metal frame on the back of each mirror helps to protect them from the weather.
Solar cooking is fun and is a clean method for cooking food. For developing countries that use wood for cooking their food, the solar cookers are great. However, it is hard for a solar cooker to compete with the low cost of electricity and natural gas in the United States. Government programs may have to be enacted to encourage conservation and alternative energy use, but in the meantime, with a solar cooker, there will be no more empty propane tanks in the middle of a cookout or waiting on the charcoal lighting process. Solar cooking does not contribute to global warming and the energy is free. So go have some fun. Cook with the sun.
See Mike Pool.