Solar Box Cookers Chris Greacen There's a lot of energy in sunlight - on the order of a thousand watts per square meter. Converting this energy into usable heat takes only an insulated box and a window. It is certainly less round about than burning trees or fossilized plants to cook food. Or worse, burning these fuels in electric power plants which send electricity miles to homes to heat ovens with giant resistors. Building solar box cookers is simple. Just apply a little common sense and go for it. Below are a couple of general designs to get you started - one I built from scrap plywood in a barn near the Home Power office, and Solar Box Cookers International's even simpler design. Home Power's First Cooker Inspired by the solar cooker articles in HP 7 and HP 9, I got fired up about trying to make one. I had no plan, but I knew I wanted the glass to be more or less facing the sun so that light would pass through the glass, not reflect off it, and that I wanted it well insulated. The size of my window pretty much determined the dimensions of everything. The cooker, when finished, was a box of 3/8" plywood with 1" duct insulation on the inside, shiny side facing in. Surrounding the window were four reflective panels: litho sheets stapled to plywood. Litho sheets are great, they are thin steel sheets used by newspapers. We got them for 25¢ for each 2' X 3' sheet. The ink washes off with kerosine, but I enjoyed leaving it making time capsules behind my reflectors. I wondered about using plywood in the cooker, we joked about it being a plywood flavored solar barbecue, but haven't had any problems. We finished at 4 pm, set it out in the sun, and soon the Home Power crew was eating a big pot of solar coos coos and a fried egg. The Solar Box Cooker International design A week later we saw a whole family of solar box cookers set up outside the RETSIE convention in Santa Clara. These units were simpler than mine and cooked great food for convention goers. The oven is essentially two nested cardboard boxes, covered (all except the outside of the outer box) with aluminum foil. There is a dead air space between the boxes a few inches thick created by balls of wadded newspaper. Four foiled cardboard strips bridge the two nested boxes, keeping the hot air from escaping from the dead air space. On top goes a tight fitting cardboard lid with a window glued in with heat resistant glue. Attached to the lid is a single aluminum foiled cardboard reflector propped up with a stick and tightened down with a loop of string. As simple as you can get - and they work - at lunch time they were cooking at a good 250”F, hot enough to bake cake and cook pounds of meat, rice, and vegies. Tips „Use sufficient insulation. Be sure to use a type which will not out- gas. Some insulations were not meant for high temperature and will break down and emit nasty chemicals. Don't use foam. Regular fiberglass insulation works well, just be sure to cover it so you're not eating insulation in your cooked food. „Paint the inside, or at least the bottom, of your box black. „Cook in dark pots with tight fitting lids. Information access „Solar Box Cookers International, 1823 11th Street, Sacramento, CA 95314. (916) 447-8691. This organization stages workshops all over the third world to teach folks about cooking with the sun. They're also working on a way to reliably kill water bacteria with these units. They've got solar cooking info. „Home Power Magazine issues 7 and 9 - each has a bibliography with solar cookbooks, etc. OOPS!!!!!! IN HP12, I got Solar Box Cookers International address & phone number wrong. Their correct address & phone number is: Solar Box Cookers International 1724 11th St. Sacramento, CA 95814 916-444- 6616 By the way, pasteurizing water is possible in a solar box cooker now. KP