On a sunny day, I can cook our dinner without any fossil fuels, and without heating up the kitchen. I have a solar oven, and it cooks using the sun’s energy directly without going through photo voltaic panels and an inverter, or any electrical appliance. A solar oven catches the light and heat of the sunshine, focusing and trapping the heat around the cooking pot and keeping the pot hot enough for long enough to cook the food.
A few years ago I made my own solar oven using several carboard boxes which fit inside each other (can you still call it concentric if it is a rectangle?). I stuffed between the boxes with shredded paper for insulation, and lined the interior of the cooking chamber with shiny aluminum foil to reflect the light onto the pot. A cake rack elevated the pot off the bottom of the box to let the hot air go underneath. A piece of glass from an old picture frame went on top to let the light through but stop the heat getting out. And a windscreen reflector wrapped around 3 sides of the box, reflecting the light from further out into the box. I supported the reflector by tying it to the upright handles of a wheeled trolley, with the bottom under the boxes, and tied it all on with a ratchet strap. The outer boxes didn’t quite come up to the top of the inner box, so I rolled up some towels to fill the gap and keep that top edge insulated too.
That home made solar oven cooked meat and 12cm diameter (450g Tuna tin) Christmas cakes really well. It didn’t get to much more than 150C even on a very sunny hot summer day, but it cooked things slowly and tenderly, with no risk of burning. After a few years of use, the cardboard began to weaken. The insulating properties decreased a lot when mice gnawed a hole and removed some shredded paper. Even putting a sock in the hole didn’t fix it well enough.
We tried making a wooden box version. It had polystyrene in several compartmented walls, and the box was lined with recut mirrors. The same trolley and reflector and glass top were used from the cardboard box, but the moisture that condensed in the box while the food was cooking posed a major threat to the integrity of the MDF.
So when I heard a good review from a friend, I decided to spend and buy a properly made sun oven. I am very glad I did. It works very well, it far easier to set up and pack away, and so I use it much more regularly. This unit reflects the suns rays into the cooking chamber from opened mirror-like metal sheets. Those sheets fold to make the oven very compact when not in use. The glass door rests against a good seal and the whole box can be tilted to match the angle of the suns rays: low in the morning and evening, so the box is tilted quite a lot, but high sun in the middle of the day, so the box tilts less. The rack is attached to the sides and swings so the pot stays level while the box tilts.
The Food is assembled just as if it were going into a conventional oven, but I find that if I put the food into a black pot with a clear glass lid is best of all. The black pot absorbs the heat, the glass lid lets it in and keeps it in. The pot still needs to be ovenproof! The solar oven gets HOT. In the picture at the top of this post the thermometer is showing 300F ( about 150C). I keep some oven mitts next to the oven while it is cooking. When I need to reposition the oven about lunchtime (to make it face the sun for the afternoon) the pot sometimes slips on the hanging rack. Better to lift the pot out when the oven is being moved, and put it back in – with some protection for my hands! Because the surrounding space is not hot like the kitchen is when the oven is on, it is easy to forget and burn my hands by grabbing the hot handles with unprotected hands.
In the middle of summer it is wonderful to be able to cook without adding heat to the house. Anytime the sun is shining enough to cast a shadow I can cook using the solar oven. I have yet to experiment with baking in the solar oven. I will write more about those adventures when they happen.