Monday, 23 October 2023 10:16

Solar Oven

The idea
The solar oven is a construction that we completed with a friend in the summer of 2022. The initial idea came after a documentary about a group of people trying to live off grid in France and after a lot of searching (there are many types of solar ovens) we ended up with this particular design. The video we got the inspiration from and followed the steps is this:
The inner chamber measures approximately 80 x 30cm and the overall dimension is approximately 1m x 40cm. The wood is plywood and the glass is fireproof. The insulation is 5cm and is made with stone wool. The black color is tempera.
At a later stage rubbers (flanges) were added internally, around the perimeter of the inner chamber for greater insulation and reflective metal surfaces on the vertical wooden walls, leaving only the base black.
Performance – use
The temperature inside the chamber of a solar oven naturally depends on how much it is exposed to the sun. Its performance is maximized if one can rotate it every now and then following the sun and of course if it is placed in a spot with many hours of sunshine. In my case, the oven is exposed to the sun until around 15.00 to 15.30 (which, especially in the summer, deprives me of several hours of operation). I have also not managed (due to other occupations) to operate it with frequent rotations. So the alternative is to have it placed where it gets the best temperatures at noon (12.00 to 14.00).
So these temperatures are around 120⁰C maximum inside the chamber, which translates to 140 to 150⁰C in the glass pyrex I cook in (it has reached 160⁰C on some summer days). This temperature (which the oven slowly reaches) is maintained from about 11.30 to 15.00 and then begins to drop slowly, maintaining a temperature of about 60-70⁰C until 18.00.
The solar oven has not yet been used on a daily basis. Despite this, it has cooked a variety of dishes, from vegetagles, chickpeas and beans to burgers with fries and cakes. It has also been used for drying carobs (for carob flour) and figs but also for heating already cooked foods.
Problems – Highlights
The cooking process is very slow. I usually put the food in in the morning and take it out in the afternoon. Because the location I have placed it is not optimal, some foods that take a long time (especially legumes) do not always have time to soften completely.
Also, foods usually need a minimum of water because the ingredients release what they have inside them and this does not evaporate. Of course, this is also the reason why they come out juicy and do not burn easily, but on the other hand, it requires attention in preparation because the final dish may turn out to be soupy.
The weight of the solar oven is an issue. Due to its large size and materials (thick wood, glass) it is difficult to move or rotate. Also, its design is such that the entire upper part has to be lifted to get the food in or out, something quite difficult to use.
The large size may also create another problem. In combination with its irregular rotation, it does not have time to heat up evenly (in the corners when there is a shadow it has a different temperature than in the center).
Suggestions - improvements
As I already mentioned, in relation to the original design I have already added rubbers for better insulation and reflective metal surfaces for more light on the food. Other thoughts are of course placing it in a different spot where it will see more sun and maybe on a round structure where it can be rotated more easily. I'd like to try to build a solar tracker sometime in the future that will do this whole process automatically (and the hours I'm away) but maybe the heavy weight of the oven will make it challenging. Finally another idea so as to solve or avoid regular rotation, is to add side mirrors so that I direct the sun towards the chamber even at times (early morning, afternoon) that it is not aligned with the solar oven.

Additional Info

  • Medium: wood, glass, etc
  • Date: 2022-2023

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