The solar cooker only works for a few hours in the middle of a sunny day, but not at night or in the mornings when people actually want to cook. Working better means working at night. Climate Healers, an international development technology organization, issued a design challenge last year after their traditional solar cookers failed to catch on in mountain villages in Rajasthan, India.

The challenge was to design a low cost stored energy solar cook stove that could store solar energy without requiring manual interventions from the user. The energy should be stored for at least an 18 hour period and should then be delivered at the users’ control to cook their traditional meals at the times that they choose, which may not necessarily be when the sun is out. People should be able to cook indoors, sitting down. The stove top temperature should be about 200ºC, with heat delivered at approximately 1 KW to the cook surface.

Three US university teams accepted the challenge in early 2011. Later that year, dozens of Indian university teams entered their proposals into the Shaastra Social Innovation Challenge at the Indian Institute of Technology, Madras. Engineering For Change has published the finalists’ papers online. The ten designs follow different strategies, using materials such as sand, aluminum cans, rice husks, water, salt, straw, or olive oil to store solar heat.

Find all the papers at Engineering For Change. Via Makeshift.

“The objective of this project is to create a solar cooker out of local invasive species and waste materials. We want to create a device that can pasteurize water and be an alternative to the use of fossil fuels for cooking food.”

“The structure of the parabolic solar cooker will be made from the canes, or stems, of the locally invasive Himalaya blackberry. Canes will be harvested and dethorned so they can be woven into a parabolic basket shape. The Himalaya blackberry canes form parabolic curves, so when they dry and stiffen they will maintain the sturdy parabolic shape of the basket.”

“To give the parabolic cooker its necessary reflective surface, we gathered around 300 tin can lids to line the inside of the basket. We punched holes in the can lids so we could string them together in lines of 8-10 lids each. Then we tied these lengths of can lids to the basket using either hemp twine or twist ties. Since there were still many spaces on the basket uncovered by can lids, we gathered a bunch of large can lids and attached those individually to the basket.”

Read more: Parabolic basket and tin can solar cooker. More DIY-posts. Previously: The bright future of solar powered factories.

Solare Brücke is an organisation that promotes the distribution of solar thermal technology, both in developing countries and in the first world. They offer detailed construction manuals, which can all be downloaded for free.

One example is the Scheffler-Reflector (see the picture on the right): “To make cooking simple and comfortable the cooking-place should not have to be moved, even better: it should be inside the house and the concentrating reflector outside in the sun. The best solution was a eccentric, flexible parabolic reflector which rotates around an axis parallel to earth-axis, synchronous with the sun. Additionally the reflector is adjusted to the seasons by flexing it in a simple way.”

The Scheffler-Reflector can be built in steel or aluminium, and there are additional manuals available for the mechanical tracking system, a stove and a baking oven. There are also plans for a solar tunnel dryer and a smaller solar cooker.  Find all manuals at Solare Brücke. Thanks to Eric Blair. Related: The bright future of solar powered factories.