Solar Cooking
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Mike Pool

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 dimensions are about the same area as a large propane grill that you might find at Sears or Home Depot. A stand can be made from one inch aluminum tubing or aluminum angle. The stand need to be 34 to 36 inches tall to put the grill surface at a comfortable working height. I found a stand that is adjustable in height and width that is normally used for an electric piano or keyboard.

A friend who buys scrap metals had some 2 inch square tubing. They were bent, some only slightly though, and were around 15 feet long. The tubing has 1/2 inch holes in each side that are one inch apart. I bought 8 tubes at a low price of $3 each. These will be the frames to hold the mirrors. Mirrors are relatively expensive compared to polished aluminum or mylar. However, I found mirrors that are called West Coast truck mirrors for $5 each. The mirrors are used as side mirrors on trucks. The mirrors already come with a nice metal holder and a threaded rod running through it. The mirrors needed to be mounted into the frame. I took off the washers and nuts that come with each mirror. I left a nut on one end of the mirror. I found some automotive rubber tubing that would just fit over the threaded rod on the mirror. I cut off a segment about 1/4 of an inch and placed on the threaded rod on each end. The rubber will provide friction when adjusting the mirrors. The nut on one end of the mirrors is used to increase the friction on the mirrors when the 2 inch steel tube pieces are pressed against the rubber pieces on the end of each mirror. A 7/16 inch allthread that is 22.5 inches long is used on each end and in the middle of the mirror frames. Nuts are tightened on each end of the allthread until the mirrors are snug in the frame. The mirrors on each frame can be aimed to about the same focal point. I wanted each frame to have a focal point at the center of the grill. This required 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. The inside rails of each frame have casters on each end.

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Pizza and cheese rolls

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. Although possible to turn the cooker to follow the sun, I have not found it necessary. I have 67 mirrors that have the dimensions 15.5 inches by 6 inches each. This gives me 4 square meters of sunlight directed to the bottom of the grill. A space is left 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. Light colored clothing is recommended. Bluejeans can get a little warm while standing behind the grill. At least most of the mirrors are on the south side of the grill.

I start cooking at around 30 minutes before solar noon. Solar noon varies through the year but for my location is around 1:45 in the afternoon. I have used a thermocouple and an Omega HH11 to measure my temperature. The highest reading was 148.5 degrees Celsius (299.3 degrees Fahrenheit) on a sunny day in September. (The pictures are from April 1 2007. I have spay painted the bottom of the grill with a bbq black paint. Even though the anodized aluminum is dark, black paint is better still for absorbing heat.) This was enough to brown the pizza crust on a 16 inch pizza in about 30 minutes. For steaks, the solar cooker works better for thicker pieces. It takes a while to put a dark grill mark on one. I would recommend fillet mignon cut 3 inches thick. I recommend that kind of steak because it does not leave much grease to clean up after. On a day earlier in the summer, I cooked 10 pounds of hamburgers in about one hour. The hamburgers were fine, but I spent 3 hours cleaning the grease spots off of all of the mirrors. Fillet is expensive but a lot easier to clean up after. I use clear pyrex lids that are used for normal cookware and glass domes to cover the food when cooking. This will capture the steam and speed up the cooking. If your are cooking a loaf of bread, just put the shaped dough on the grill and turn a pyrex bread pan upside down over it. It is faster to just make flat bread though. Frozen corn is one of my favorite things to cook. The corn gets a slight roasting on the grill.

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Pizza is cooking!

I had piece of low iron glass cut to fit just inside of the rim of 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 a little more light to pass through than plate glass. Currently, low iron glass is still too expensive and our local glass company had to order it. The glass is tempered and 3/8 of an inch thick and is the thinnest that I could order. I am not sure if you really gain anything over a thinner piece of plate glass. Iron makes glass have 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. 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 a windshield reflector for a car. 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 mirror side pointing towards the house. The metal frames behind each mirror help protect them from dust or the occasional hailstorm we seem to get around here.

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Pizza is done!

Solar cooking is fun and is a clean method for cooking food. For the third world countries that use wood for cooking their food, the solar cookers are great. But it is hard for a solar cooker to compete with the low cost of electricity and especially natural gas for cooking 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 for charcoal to light and get ready. Solar cooking does not contribute to global warming and the energy is free. So go have some fun. Cook with the sun.

Contact

See Mike Pool.