In early April 2010 I made my first attempt at building a solar cooker & tested it in Death Valley, California. My aim was to build a functioning cooker for minimal cost that required no specialist tools to assemble.
Solar cooker components
- Cast iron pan ($10)
- Reflective car windscreen shade ($5)
- Gaffer tape ($3 roll, only used 6 inches)
- Turkey roasting bag ($2.50 for 6)
- Aluminium cooking foil ($1.50 for 50 metres, used about half a metre)
- Cardboard (free)
Tools / equipment
- Car key (used to cut through windscreen shade)
- Thermometer used to test internal oven temperature
- Beer - to drink while watching the cooker do it's stuff
Solar cooker construction theory
The reflective shade directs solar radiation (sunlight) onto the cast iron pan which, being black, absorbs heat. The turkey roasting bag helps to retain the collected heat - like a greenhouse. So, the heat inside the bag should steadily rise as long as the cooker is pointing towards the sun.
The initial build
The initial build can be seen in the main picture above. It took all of 10 minutes to put together. The windscreen shade had slits ripped into it with a car key to make it easy to shape into a rough parabola. Gaffer tape was used to hold the parabola in shape and a sheet of cardboard covered in aluminium foil was taped to the bottom of the parabola.
Then I filled the pan with cold water, popped the thermometer into the pan and placed it in the roasting bag which was sealed using a twist tie that came with the roasting bags. This was then placed on the floor of the cooker.
The cooker was angled to the sun. After a short while I made some high tech modifications - 2 large stones were place on the floor of the cooker to stop it wobbling around & I modified the top part of the parabola to reflect more light onto the pan. The mods can be seen in the photo below - I think they lend a certain 22nd Century whizz to the whole affair.
Death Valley in early April should be renamed Quite Pleasant Valley. I had it in my head that the temperatures would be around 30C to 40C and they actually were the week before I got there. However, when I arrived the temperatures were in the mid to upper 20s.
The cooker was first pointed at the sun at 4pm. This isn't ideal, as the sun is pretty low in the sky at that point - I think it would have been better to start mid morning and cook from 11am to 3pm.
That said, the results were good. Within half an hour the internal temperature of the oven was 140 Fahrenheit (60 Celsius) and after an hour it was up to 180 Fahrenheit (82 Celsius). It peaked, briefly at 190 Fahrenheit (88 Celsius) before tailing off as the sun got lower in the sky. With results like that I'm confident that starting earlier in the day would have allowed time for proper slow cooking of food.
The photo below shows steam and condensation gathering in the pan as it began to accumulate heat. The temperature was about 160F at the time.
You can build a serviceable solar cooker for low outlay that will work in warm, not hot, sunny conditions.
I'm going to play with this design and others to see whether one could be built to work in the UK - I'm thinking that the cooking area will need to be well insulated and that another black metal heat sink will be needed to achieve decent temperatures.
I'm also returning to Death Valley in August when the temperatures will be extremely high and I will repeat this experiment then.