Energy SystemsProcessing & Food Preservation

Solar Tyre Cooker


Sketch showing the solar tyre cooker

With relatively inexpensive materials and easy to construct, a solar tyre cooker can be a very useful device for many of the poor people in the world. In many African countries people walk long distances to collect firewood to cook their food, or spend up to 50% of their income buying wood or charcoal. The materials needed to make this solar oven are very cheap and fairly easy to get hold of, making this a great way to cook food that saves fuel wood and money. This can also be useful as an off the grid cooking device.

What you need

An old tyre, a glass square big enough to cover it, a black pot, silver foil, newspaper, tape, cardboard, something to weigh the glass down… and some sun!


Materials needed to construct solar tyre cooker

Construction Steps

Step 1: Place the cardboard on the ground, making sure that it is flat. This acts as extra insulation for the oven.


Flat cardboard at the bottom

Step 2: Put the tyre onto the cardboard. Check that there are no gaps between them. The tyre absorbs heat from the sun.


Tyre on top of cardboard

Step 3: Add newspaper all around the inside and the base of the tyre. The newspaper traps air and adds more insulation.


Newspaper as insulation material

Step 4: Put a base of silver foil inside the tyre to reflect the heat.


Silver foil to reflect heat

Step 5: Add a long length of silver foil all around the sides and inside of the tyre. This acts as your main solar reflector (like a mirror).


Silver foil lining

Try to make sure that there are no gaps. Then tape the ends together.

Step 6: Tape the edges of the square of glass to avoid accidents. A circular piece of glass will be even safer.


A clean glass sheet

Step 7: Place a black pot into the middle of the tyre; using a black lid is even better. Try a stew without much water content at first.


A black pot with pumpkin and rice stew

Step 8: Put the glass on top of the tyre, ensuring there are no gaps. Add some weights to avoid heat leaking out of the oven.


Glass sheet on top of tyre

Step 9: Make sure that your oven is in full sun with no shadows. Leave it for about 3-5 hours, depending on the strength of the sun and what you are cooking.


Leave it in sun

Check your food to see if it is cooked. Try not to let too much heat escape – be careful, it may be very hot. Then taste it!


Enjoy the cooked food

How it Works:

Solar radiation enters through the glass and the UV light is trapped inside the oven. Light reflects off the silver foil and warms the heat-absorbing black pot. Heat is kept in the oven by the newspaper and cardboard insulation. The black tyre absorbs the heat and heats up the whole cooker. Additionally it adds extra insulation to the whole device.

Under strong sunlight the temperatures inside the tyre rises up to 100ºC within 2-3 hours. Individuals who have tested this device have been able to boil water in two hours. On a cloudy day the temperature rise is less and one may have to leave the pot in the sun for longer.

Watch these two video’s below to get a better understanding of the solar tyre cooker.

A bit of concern:

Though the simplicity in construction of a solar tyre cooker may naturally draw an individual to give it a try, there may be some concern about using tyres for cooking food. Tyres are known for off-gassing and leaching of toxic chemicals when exposed to natural elements. Most of the off-gassing happens during the first year of usage and typically a tyre is discarded after 3-5 years. The level of off-gassing and leaching of chemicals may have reduced in used tyres, but still the process continues at a slower rate (4). This aspect needs to be further investigated.

References:

Ravindra Krishnamurthy

Ravindra Krishnamurthy is a freelance science writer covering science, tech, the environment, health, food, and culture.

4 Comments

  1. Are you sure it is UV light that heats the food? I thought it was the infrared radiation and visible light.

  2. Wouldn’t a black material be better at creating heat than a reflecting one? The former turns visible light into infrared radiation, which can’t pass the glass well, the latter just reflects the energy back in the same wavelength which can pass the glass.

    This spring, I built myself what was supposed to be a mini cold frame so my salad seedlings wouldn’t die when I put them out for the day to soak up some sunlight. (The weather was still freezing in the night, so planting them out wasn’t an option.) The construction consisted of a shoebox-sized box made of 4 cm thick styrofoam (used by pharmacies and laboratories to receive shippings that need constant refrigeration; afterwards they often land in the trash), covered on the inside with a dark grey plastic trash bag, a pane of transparent plastic on top (less insulating than glass), and a brick inside for thermal mass. Plus a digital thermomenter to test the thing. On a sunny day in early March (outside temperature maybe 10-15°C), that thing reached 60°C in less than 20 minutes, and fried my salad seedlings – literally while I had my back turned for a moment. I didn’t keep the box closed after that, but I’m sure I could have cooked something in it given some more time.
    Note: I live on the same lattitude as Calgary, Canada, so the sun still stands rather low in March.

    Currently (late May), I’m measuring 60°C in the open, 10 cm in front of a south-facing wood wall painted dark brown. The temperature on our brown roof tiles regularly reaches 40-50°C on sunny days. But the general air temperature is just 25-27°C on those days.
    On the other hand, I have south-facing roof windows right beside the measuring point of the above mentioned roof thermometer, and the cloth shades on the indoor side of the window glass are painted silver on the outside-facing side, precisely so it won’t get so hot in here. If I remember to close the windows so the 40-50°C air from the roof doesn’t blow in, it stays below 26°C in this room. If I don’t put down the silver shades, it easily gets above 30°C on sunny days. (AC isn’t really done in my country. The rest of the house doesn’t have south-facing windows, but thick brick walls and heavy outside rolling shutters made of metal or wood for almost all windows, which are much better for insulation than indoor shades. So the rest of the house stays around 21-23°C even in the summer.)

    1. Yes Vivi, the container needs to be black so that maximum amount of sunlight is absorbed. The intention of putting reflecting surface like aluminium foil is to gather more sunlight and concentrate it towards the central black colored cooking vessel.

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