DIY: Solar Cooker

Every time I go out in the sun, and get some sun burn, I wonder why we (I) don’t use the solar energy? and this lead me to a frugal way to harness this energy and get some ‘ Do It Yourself’ satisfaction. So here is a solar cooker that I made and cooked ..err..under cooked some rice and veggies. Along with the making of the cooker, sharing some fun troubleshooting methods.

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My solar cooker at work

Material for making the cooker: a big cardboard box (1no.), scissors, cardboard cutter, aluminium foil, black color, brush, masking tape, acrylic sheet, scale, and pencil.

Material for troubleshooting: a sock (washed and cleaned), a shampoo bottle, a broom with long handle, clothes drying rack.

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Material for making a solar cooker

I had a big movers box 2ft x2ft x 1.5ft (600x600x450mm) that I opened for making a prototype for one of my design projects.

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reusing cardboard from my previous design project

I reused that piece of cardboard to make two boxes that would fit into one another such that there is at least 1 inch (25.4mm) gap between the walls of the two boxes. In this gap an insulating material is added, polystyrene (Styrofoam or Thermocol) are used but I wanted the cooker to be eco-friendly, so I used left over cardboard pieces and inserted them in the gap. To make sure the insulation stays in place I used masking tape to stick them to the walls of the larger box. The larger box has a flap that can close the box.

Dimensions of the large box came out to be 23 inch x 13 inch x 6 inch and for the smaller one 18 inch x 9 inch x 6.5 inch(for mm multiply by 25.4, that’s lot of math;))

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Large box with a flap and insulation.

I glued the aluminium foil to the vertical walls of the small box and painted its base with black color. The foil will help reflect the sunlight on to the cooking pan and the black base to help heat absorption.

 

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Small box with black painted base and aluminium foil vertical walls 

I then glued aluminium foil to the flap of the large box which will be the main reflector and then placed the smaller box in the larger one. I then glued aluminium foil over the gap between the two boxes. However as height of my inside box was 0.5 inch more than the outer one, the foil had a slope. Ideally it should be flat or slope inwards. Mine sloped outwards and I suspected that it won’t be good for reflection or insulation.

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The cooker is ready without the acrylic sheet.

With all enthusiasm I wanted to test if it works and hence I placed a steel pan to cook some rice in it but had no glass or acrylic sheet to use as a cover. I rummaged through my book shelf and found an acrylic certificate holder which I split into two and placed over the box. This transparent cover would help to trap the heat inside and that will cook the food!

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Rice being cooked.

I placed the rice in the cooker, covered with an acrylic sheet, adjusted the angle of the reflector flap (flap of the large box) and set it in the sun at 1:30 p.m…..came back at 2:30 p.m. to find that the flap has covered the box, thanks to the wind. At 2:30 I again adjusted the flap angle, this time supported it with a shampoo bottle in front and the building wall at the back. At 5:30 hoping to see a nice steaming rice I checked the cooker and nothing was visible as the water vapor gathered on the acrylic sheet. To my disappointment the rice was as it is, however hot water was the saving grace.

Next day I was determined to complete my testing but probably sun god didn’t want to ruin my faith in my design so soon and hence for the next 12 days he didn’t show up :(.

Finally it was a clear sky on Tuesday 29th May temperature was 24 degree Celsius (75 deg F) and I set out the cooker at 2:00 p.m. This time wanted to steam some guar (cluster beans).

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Guar (cluster beans) being cooked, this time with all trouble shooting in place. The cooking pan covered with a glass lid to avoid water vapor collection on the acrylic sheet, a sock to block a gap between the acrylic sheet and the box, shampoo bottle to maintain the flap angle in front, a long broom stick at the back of the flap (see the green stick) to prevent the flap from falling behind. 

I also placed a thermometer inside the box to see the temperature rise, in case the beans don’t cook.

20180529_135448Thermometer in the box: Humidity 42% temperature 30 deg Celsius at 3:00 p.m.

At around 5:00 p.m. the thermometer was stuck at 88 degree Celsius (190 deg F)and intensity of  the sun was going down.

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The under cooked beans 😦

Finally at 5:30 with no change in temperature I took of the beans. The beans were under cooked but the water was hot enough to dip a tea bag.

Still waiting for the Sun to be intense as my cooker looks promising. It raised the temperature from 24 to 88 deg Celsius, though not enough for cooking the cluster beans but good enough to make a guar flavored tea 😉

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