Adventures in Cooking - Building and Using a Simple Box Solar Cooker
By Vic Hanson
I don't remember for sure exactly how this project got started but I was over at Brad and Gina Shaw's house here in Cotahuasi, Peru, where we work as missionaries. Brad was talking about trying to make solar cookers to help the people here. One of our church members was looking for a new burro to replace his mother's burro that had died. She needed the burro to haul firewood for cooking. Because Cotahuasi is a large village and a majority of people still use wood cooking fires, the nearby sources of firewood have been depleted. It takes her a full day every week to go and get a week's worth of firewood. Without a burro, she would have to go oftener and bring back less wood each time; only what she could carry on her back. Our area usually gets eight to nine months of sunshine a year so solar seems like a good option for a supplemental cooking source. Brad also mentioned the need for more fuel-efficient wood stoves, rather than just a fire on the ground with three stones to support the pot.
Brad had seen a large parabolic solar cooker in Tomepampa, a village about 20 minutes away. He suggested we go look at it so we hopped in the car and went right away. The cooker wasn't at the home where he had previously seen it, but they told us where it currently was and we were able to go and look at it. It was about five feet in diameter, made of shiny sheet metal attached to a framework of angle iron and a parabolic dish made of one-inch wide metal bars. We were told that it cooked quite rapidly and worked well, so we took measurements and lots of pictures to guide us in making one. However we knew it wouldn't be an immediate solution to the mother's problem because the shiny metal wasn't available here in Cotahuasi.
That evening I did some research on the Web to learn as much as possible about solar cookers and hopefully find some plans for building one. I did see a photo of one that looked very similar to the one we saw, but there were no plans for making it. One of the best sites I found was that of Solar Cookers International, based in Sacramento, CA. Their website is included below, they have many different types of cookers and the plans to make them available as downloadable PDF files. I was anxious to make one right away, rather than waiting until after my next trip to Arequipa where I could hopefully find the materials for the large one we had looked at.
They had smaller parabolic ones, some of them using an umbrella for the parabolic form, others required building your own out of cardboard or wood. The plans that caught my eye were for a box cooker, lined on the inside with aluminum foil and using a piece of glass on top to trap the heat inside of the box. That appeared to be the easiest to build with the limited materials I had available, especially as I could see a large box on a pile of stuff on the other side of the room from where I was sitting at the computer. I excitedly went through the list of materials to see what else was needed. I soon found a big problem; I didn't have any aluminum foil. They didn't recommend using glass mirrors, which I knew I could get in Cotahuasi, and aluminum foil wasn't available. The mission of Solar Cookers International is to promote solar cooking in third world and developing nations, where many people are still dependent on wood fires. The plans had a section on substitute materials that could be used in areas that don't have access to all of the normally used items. Instead of aluminum foil, it said that aluminized polyester film (MylarŪ) could be used, although I didn't notice the warning until after I had built the cooker. It said not to use it on the inside of a box cooker because it could melt and give off fumes, but neither of those has been a problem.
I knew I had seen some material like that somewhere in my house so I started searching around. I soon found it! Every morning I have a half of a small bag of Angel Zuck Cereal for breakfast. It is available in larger bags but they are more expensive per gram than the smaller ones, as is often the case here in Peru. They are "plastic" bags but the inside is a shiny reflective surface, just like the Mylar balloons that are so popular. I dug through my garbage for as many as I could find there, and then emptied a few more bags into a plastic container to come up with what looked like enough to line the inside of the box. I buy the cereal by the case and now I had an empty cardboard box as well as the empty bags. About this time I came up with the exciting idea of packaging everything needed to make the solar cooker, along with instructions, inside the large cereal box. Then you could give the whole box to a needy family, they could eat the cereal and then make the solar cooker!
I soon realized that this wouldn't work as you need two boxes, and one has to be larger than the other, along with a piece of glass too big to fit into the cereal box. So I went and got the first box I had seen, it had contained panetone, which is a Peruvian fruitcake, popular at Christmas time. The boxes weren't quite as big as recommended, but the cereal box would fit perfectly inside the panetone box, leaving room to put the necessary insulation between the boxes. It was now late and I needed to get to bed, but I could hardly wait until morning to start building the cooker.
I had everything I needed now except the glass and the adhesive to attach the shiny plastic to the box. Still trying to make it as simple as possible, so that those with limited resources could duplicate it, I checked the substitution list and was reminded that you could make a paste from flour and water. I started on the construction and all was going well. I used crumbled up newspaper and cardboard scraps to insulate the airspace between the boxes, although it says you can use dry plant fibers, feathers or wool, items most people here would have, but I didn't. When it came time to attach the plastic foil, I mixed up some flour and water paste and attempted to glue the foil onto the inside of the box. But as the directions also stated, it can be hard to get it to stick. The flour paste didn't hold it at all so I had to go buy some glue at the stationery store. That worked better but still didn't hold the edges well, plus there were lots of bumps and wrinkles in the foil. The directions also said not to use tape on the inside of the box, but I had some high temperature shiny foil tape that I had bought in the U.S. so I used that. I use the tape to make ultra light backpacking stoves out of aluminum soda cans (search the web for "Pepsi can stoves" if you are interested). I did feel bad about using something that I didn't think was available here, but I just saw a similar tape at the new Maestro (Ace Hardware) Home Center in Arequipa.
The only thing left now was to make the lid for the cooker, which takes another piece of cardboard, that came from one of my storage boxes (originally my kitchen stove box). I have a friend who used to have a hardware store here; he came by while I was working on the cooker. He said he would be gone all day but he still had some glass and would cut me a piece when he got home in the evening. However he never showed up and didn't answer my phone messages. After a few days I gave up and went to the glass shop to get a piece there. The owner was out of town and the shop was closed. It was about two weeks later before he got back and I finally found the store open to get the glass. Finally I finished the cooker, but it was too late in the day to try it out. I was very eager to test it the next day but then we had a couple of unusual cloudy days during our normally sunny dry season.
At last the time arrived, a beautiful sunny day. I decided to keep it simple for the first try and just made plain white rice. I put too much water in it so it was quite sticky, but it worked! It was time for the real test - pot roast. The beef here is not hung and cured, so it is normally very tough. A crock-pot slow cooker works the best for making a pot roast, taking about eight hours on low. It was a perfect test for a solar slow cooker. On my first try, the weather turned cloudy after about 4 hours so I had to finish it in the oven. Then I was busy (and there were a few more cloudy days) so I couldn't try it again for a couple of weeks. It also isn't possible to buy roast beef here every day. It is usually only available a few times a week, early in the morning (6 or 7 am) on the day they butcher. I stopped at the meat market and the owner said they would have some early in the morning so I asked them to hold two kilos of boneless beef for me until I got there.
In the morning, after getting the beef and peeling carrots and potatoes, it was 10:30 before I set the cooker out in the sun. I turned the box every two hours or so to keep it aimed at the sun, and brought it in at 4:30 when the sun went behind the mountain (a disadvantage to living in a canyon - late sunrises and early sunsets). It smelled so good and it looked done, just like in the crock-pot. The taste test confirmed success, all was cooked and the beef was fairly tender. On my second try a few weeks later I set the box out in the sun to preheat while I was cutting up the veggies, and then browned the meat in a fry pan like the crock-pot recipe book says, to give it a head start. Again it was good, but not falling apart tender like eight hours in the crock-pot. Looks like I will have to get up earlier next time and have it ready by 9:00 when the sun hits my cooking area.
Besides making a larger, parabolic cooker, I plan on experimenting with more efficient wood burning stoves as well.
If you are interested in making your own box solar cooker, or the "Cookit" a simpler panel cooker, you can download the file SOLAR COOKERS How to make, use and enjoy 10th Edition, 2004 at http://www.solarcookers.org/
Vic Hanson is the founder of Adventure Cotahuasi Tours, which offers pre-planned and custom adventure travel tours in Cotahuasi Canyon and other areas of Peru.
If you are interested in your own adventure in Peru, check us out!
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