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Passive Solar Research
Solar Cooking Research
As part of this project, we have been researching solar cooking. We have experimented with various designs, and will continue to post our results as we
learn more. We have built about 7 different designs, and will explain pros and cons below.
This is our most current model, that we have built for Broadened Horizons Farm. It has four reflectors and is large enough to cook for 4-7 people. The exterior of the box and the reflectors are made from 1/4 inch Luan, keeping it lightweight and attractive. The reflective material is heavy duty aluminum foil, and the insulation is recycled cardboard and newspaper. Because we used recycled materials, the cost of materials was only $20 dollars. We have been using this cooker through the winter here in East Tennessee, with good success. We cooked a delicious Thanksgiving turkey, and have been cooking dishes such as cornbread, beans, rice, vegetables, chicken and potatoes, squash, pumpkin pie, bread, etc. During the winter it has reached a temperature of 325 F. The reflectors fold in for easier storage. Initially we only used 1 reflector, then adding 2, before finally settling on 4 reflectors. The improved performance was dramatic with the use of 4 reflectors.
During the summer of 2006, we built a similar but smaller model, and used it to cook around 80% of our food in NW Washington State.
This is the Solar Cooker we used on the sailboat. It is very compact and dense so as to be more stable in wind and chop. The design is somewhat unique in that it uses a black tube as a heat chamber, so you don't need a black cooking container. We did most of our cooking inside canning jars. It is built with aluminum flashing and mirrors as the interior reflectors, a piece of stovepipe painted black as the heat chamber, and foam board as the insulation. We found that it is very diffilcult to use a solar oven on a sailboat when underway, as the boat is always moving making it hard to focus the cooker on the sun. We were able to use it anchor or when tied up to a dock. At first we tried using it with no reflectors, and it would not reach temperaturs above 180 F. We then tried one and two reflectors, and it reached 220 F. With more reflectors it would reach higher temperatures.
These are very powerful collectors that focus the sun’s rays onto one spot, potentially reaching very high temperatures. It needs to be focused often to achieve maximum energy, and you have to be careful not to look at the shiny spot. Dark Sunglasses are recommended when working with these cookers. The one that we made is about as simple as one could get. It is just a piece of aluminum flashing bent around in a half circle, with the dark cooking pot in the center. There is a plastic oven bag (withstands temperatures of 400°F) surrounding the cooking pot to help hold in more heat. This simple contraption reached temperatures of 250°F.
This is a type of cross between a box oven and a parabolic focuser. It is compact and easy to make. This one is modeled after the Bernard Style Cooker, but is made out of Aluminum flashing rather than cardboard and aluminum foil. It uses a heat resistant turkey bag around the black pot to hold in heat, a similar principal to the solar oven model. It reached temperatures over 200°F, with an ambient air temperature around 60°F, during early November, in East Tennessee. It does not need to be focused quite as often as a parabolic cooker, but still needs more care than a box cooker. These are the easiest to build, and a similar model, the Cookit, has been widely built all around the world.
Through this research we have learned a few lessons. There are simple things that make the cookers more effective. The size of the cooker is important, as a certain amount of reflected sunlight is needed to reach cooking temperatures. The more sunlight you can focus on your cooking vessel, the more energy there is to cook with. Raising the cooking pot off the ground a little bit seemed to help (we used little rocks or a rack of some sort). We tried using two bags to increase the amount of trapped heat, but it did not seem to add much benefit. Out of these three different styles, the box cooker was the easiest to use and the parabolic focusing has the most potential for high energy applications. In using the box cooker, it became clear that this device actually make cooking far easier and more convenient than cooking on the stovetop, contrary to what many people might think. The reason for this is that food can not burn and cooks evenly without stirring, so the cooker can be set up and then left to go and do other things. After you finish what you are doing, you come back to the cooker and the food is done, hot, and ready to eat! It saves time and energy, two things in high demand in our modern lifestyles. For more info on solar cooking and free solar cooker plans check out www.solarcooking.org
Solar Tube Shower
(This is an Exerpt from our pilot project to the Gulf of Mexico in 2005 to read more about that trip click HERE.)
When traveling on the sailboat, the simple act of taking a shower becomes an incredible luxury. We carry 40 gallons of fresh water; precious water that has to sustain us for weeks at a time until we get to our next port. Fuel and electricity are also precious commodities, and living aboard really puts a person in touch with how much they use. Having a shower aboard is like having a Jacuzzi on land. How to do this has been a question I have pondered since we began this journey.
Before the trip started, we bought a Sunshower. This is basically a black plastic bag with a tube coming out the bottom. While this helped, it was only 2.5 gallons and didn’t have enough pressure to wash the soap off easily. The nice thing about it is that it can be rolled up and stored out of the way when not in use, an important quality on a 30 ft “island”. It wasn’t nearly enough for the 3 of us, and was rarely used.
After building the 150 gallon solar showers for Four Directions Solidarity Network, I had a 5 ft piece of 4” pvc pipe left over. I also had an extra end cap left, and thought that if I put the cap on one end, a shower head on the other end, and painted it black, we would have a solar shower. It seemed like it would work, so that is what I did. After getting it all assembled and hung in the rigging above my head, I had my first shower, and it worked!
Next came the continued R&D. Our friend Jack, a fellow inventor, wanted to refine it a step further. As a contribution to our project and our hygiene(we had been jumping in the shower on his boat after work to wash off the day’s sweat), he bought all the components for all three of us to have our own solar tube shower. We made a few changes in these new improved models.
First, we started with black tubing, eliminating the need to paint it black. We made them 7 feet, the maximum length that would fit on deck. Every foot equals one gallon of water, so each one holds 7 gallons. Next, we made our own showerhead out of a ½” pvc cap with holes drilled in it. This way we can fill it from either end, depending on the circumstance. We also added a small vent screw in the end so that we didn’t have to open the cap to allow the water to flow freely. After building three of these new and improved solar tube showers, we now had 20 gallons of shower waiting for us. We even got a volunteer to test them on, and they worked great. We have a line tied to both ends, and when we are ready to take a shower we attach the peak halyard to the end of the tube and hoist it up above our heads, securing the other line to the shroud so it stays in position. When we are done, we lower it down and fasten it securely on the deck amidship. When we are underway for extended periods, we can refill them with rainwater, and they take no electricity or fuel to operate. After a long day in the sun at the tiller, being cleansed by fresh water feels so good. Ahhh