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Summer time is often for me a time to relax in the garden with a book and cold drinks. But sometimes it is also the time to experiment with other techniques then electronics. And as I was intrigued by some stories I read about solar ovens I decided to experiment abit and build one myself.
Solar oven ???
For those not familiar with the name I give a short explanation. A Solar oven is exactly what the name suggests. It is an oven that heats its inside by solar energy. No not the solar panels that create electricity but use the warmth of the sun direct.
The basics are very simple.
Use a carton box. Coat its interior with black paint. Glue aluminium foil to the inside of the lid. And cover the box with some plastic foil.
The black coating absorbs the heat inside the box and the plastic foil makes sure it can not escape. The lid with aluminium foil is used as a reflector to direct the sunlight to the box's inners.
The build.
Coating the box is simple. I used black paper which I glued to the inside. The edges were not totally covered but that's ok for my first prototype. Next I glued aluminium foil to the lid. This is common household aluminium foil. It's only purpose is to reflect the sunlight into the box for extra heat.
The problem was the plastic foil. It just did not want to stick to the sides of the box. And this is a crucial part for the solar oven. The plastic keeps the heat inside the box. It does not have to be airtight but it needs to close the box enough to prevent the major part of the heat to escape.
My 3D printer to the rescue.
On thingiverse I found a kind of bookmarker. 
I already used that as .............a bookmarker. But I imagined I could use this to secure the plastic foil.
The result.
Unfortunately lately the summer weather is not very good. It's raining a lot and that keeps the sun away. However I managed to do a few tests.
I put a small dish into the solar oven and put a mashmellow in. I aimed the lid at the sun in such a way that it reflected the sunlight into the box. After about an hour the dish was hot. Real hot as in burning your fingers hot. The marshmellow had melted. Not in like it got fluid but it melted so much that it was totally soft and sticky.
And guess what ?? It worked with chocolate too. The chocolate just melted nicely, and I could dip some cookies in.
It's also good for defrosting food. And guess what it is environmental friendly cause it does not use any energy when it is build.
Next step
Next step is to put some electronics in. Nothing fancy. Just an ESP with a dallas DS18B20 to measure the temperature inside.
And I need to make some kind of hinge that holds the lid at such an angle that it reflects the sun best. I now used plants for that, but that was just improvising.
A lot of ideas to experiment with. And fun to play with. I just let the sun do its job while I was sitting with a good book and cold drinks.
Have fun
Till next time
Luc Volders