The No-Tech Solar Oven - By Nev Sweeney

solar oven I love the idea of using the sun's energy directly, no pollution, no waste and no (energy) cost, it's fun to experiment with to dry or cook food or generate electricity and helps you become more independent from the power grid. A couple of years ago I became interested in solar cookers, the obvious answer for when you have no fuel to cook your meals with, you want to increase your level of self sufficiency, do something good for the planet or you just want save money. It was one of those ideas that was just so good!

After a quick trip around the net I found www.solarcooking.org with plenty of low or no tech plans for building solar ovens and after some consideration I decided I wanted to build solar box cooker, this is basically one cardboard box inside another, with a clear panel to let the sun in (construction details to follow). It was mind bogglingly, cheap and easy to build, real alternative technology ...............and it worked like a heap of crap!

I made it as per instructions, tried to cook a number of dishes using several different food containers and the best that I could do was attain 60°C and that was in full sun! (editors note and Nev lives in Australia!) All it would do was warm the food and after a full day in the sun I still had do most of the cooking in the gas oven.

solar oven insulator boxes The principle or theory that I was working on was that the inside box was insulated by then outside box and the inside box was then lined with aluminium foil to reflect the sunlight back onto the cooking pot once it had made it through the clear panel. So much for that theory! So I put it away in the shed and forgot about it for a while.

After doing some more searching on the net I solar oven showing the matt black steel plate found a small footnote on another website where a Guy who had been experimenting on his own account said that the secret was to have thin walled, matt black painted cooking pots and a matt black steel panel in the bottom to absorb the heat. This heat was then passed on to the cooking pot, in direct contact with it by conduction. This was exciting stuff and sounded like a serviceable new theory, but would it work?

Well, I put in a matt black steel panel and bugger me, it did! All of a sudden I could get up to 90°C and was able to cook an aluminium billy full of spuds perfectly in less than two hours. This technology made sense and worked fine if you set it up right. So before I get too carried away, here is how I made the no-tech solar oven -

Construction details

Get hold of a large cardboard box, a smaller cardboard box (one which allows at least an inch of dead space all around once it is inserted in the larger box) a Glad or equivalent oven bag, some aluminium foil, PVA glue and the steel plate with some matt black paint.
Centre the bottom of the smaller box over the top of the larger one and, using a Stanley knife or equivalent, cut a hole in the top of the larger box so that the smaller one can slide into the larger one.
Now line the larger box with aluminium foil, shiny side out. This can most easily be done by getting hold of some PVA glue and a paint brush and painting the glue onto the cardboard and then smoothing on the foil. If the glue is a bit thick to use a brush, thin it down by mixing in a bit of water.
Cut the corners of the top of the smaller box into flaps and fold them out so that they support the smaller box centrally in the larger box. If you are going to insert insulation this should be done before the flaps are glued into place, locking the smaller box into the larger one. The insulation could be crumpled newspaper, straw, wool, polystyrene beads or what-have-you, anything that provides insulating dead-air spaces.
The smaller box may now be lined with aluminium foil, also shiny side out.
Once the inner and outer box are assembled and glued, the lid can be made by placing a flat piece of cardboard over the top of the double box and cutting it to leave a 25mm edge all around. The line where the box sits can then be scored and the ends cut to form flaps, the flaps are then folded down and around at the corners and glued, forming a tray shaped lid. This lid then has a three sided cut to put in the top of it to form a large flap the size of the inner box and then tape an oven bag over the hole to form a clear window to let the sun in.
The bottom of the flap should also be lined with aluminium foil to act as a mirror to reflect sunlight into the oven. A Z-shaped piece of wire is then inserted in the edge of the flap and the top of the box to keep the flap open at the right angle to act as a reflector.
To finish off the oven cut a piece of sheet metal to fit the bottom of the inner box, and hit it with some non-toxic matt black aerosol spray. Install the plate and your ready to cook!

All it took was a couple of hours work and very little outlay (mostly for the oven bag) and I had raised my level of self sufficientish a notch! Well worth a go.....if I can do it, anyone can.

Nev