If you didn’t have readily available access to electricity or natural gas, how would you heat food? In many areas of the world, this means burning biomass directly, whether through wood, coal, dung, or other available materials. Besides potential negative atmospheric effects, and ecosystem damage from over-harvesting of wood, cooking with biomass, especially indoors, can present serious health consequences.
If all of that wasn’t enough, the time spent collecting fuel to burn, or the expense of simply buying it, can have a serious economic impact on the people that cook this way.
On the other hand, the sun continuously beams a vast amount of energy to the earth. The challenge, of course, is collecting it and using it efficiently, a challenge which Chris Pickering, who lives in Melbourne, Australia, decided to take on with his solar oven.
According to the project writeup, the oven he made has been tested to be able to reach a temperature of 266 degrees Fahrenheit. However, Pickering has since obtained a better thermometer and clocked a temperature of 300 degrees inside! A couple of sausages are seen cooking on his site, but with this expanded capability, he hopes to even cook a pizza with it.
It’s really an amazing thing that by concentrating the sun’s power using a relatively small fixture, this kind of temperature can be attained. Besides focusing the beam via an octagonal structure that sort of resembles an old record player, Pickering also added a mass to absorb heat energy in the form of several lengths of rebar attached together.
This mass is important to keep the temperature from dropping dramatically if the sun’s light is lost temporarily via cloud cover or poor aim. The mass also affects the amount of time it takes to preheat the oven. With the rebar installed, it takes about 30 minutes, though if you were to substitute a smaller mas, like a cast iron pan, this time would be reduced significantly.
The build is designed to be easy to make, using cardboard, aluminum, and recycled wood for the base. You can see some of the steps, as well as pictures of the Sketchup CAD model in the gallery above, but more information is available on his website. He tried to made his design easy to replicate, and according to him:
I spent a few summers teaching teenagers how to build scale model buildings on behalf of Games Workshop back in the early 2000’s, so I have a reasonable idea of what’s too easy or too hard for beginners to build. The octagonal design is rather simple – since each layer starts with 4 rectangles, and is them connected by 4 more identical shapes.
Even if you screw up the measurements a little on the more difficult triangles and trapezoid pieces – your solar array will still end up being symmetrical as long as you trace your pieces from the first one you cut.
This is just a prototype design, but I’ll stick with these easy-to-build principles on all future versions.
One thing that could have been a challenge, but did work was the fact that this oven just barely fit through his door to get outside. He advises building it slightly smaller if you have undersized doors. Perhaps you could instead build it outside or in a garage, where Pickering stores his.
Longevity is a question I had about this design, and he reports that thought the octagonal design is quite sturdy, if it was left out in the rain on a windy day, it would probably be destroyed quickly. As this is a prototype, he’d like to make this design out of more durable materials, perhaps in such a way that it could be left outdoors all the time, or in a configuration that could be folded away for easy storage.
A version using sheet metal came into my mind while looking at this project, but Pickering doesn’t see that as a good solution for those currently using biomass to cook out of necessity. According to him:
Sheet metal wouldn’t work too well unless is was aluminum, since that won’t rust – but is very expensive. Low income families also don’t really have access to sheet metal tools and materials – but I do plan on doing a version with reflectors crafted from aluminum cans riveted to plywood.
He definitely brings up a good point given his goals with this project, though a derivative project using more expensive materials is a tempting idea. Be sure to check out the video below of him showing off his build!