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Off Grid Energy Independence
Posted on May 02, 2018 by Dr Peter Harrop

Photovoltaic cooking makes sense

Modern energy harvesting from solar windows to solar roads is about much more than replacing grid electricity: cooking, heating and other high-power activities currently using fossil fuels are now a target too. See the IDTechEx report, Off Grid Zero Emission Electricity 2018-2038.
 
Three billion people still rely on traditional biomass-based cooking. They are vulnerable to health and fire hazards and it increases global warming too. Consequently, solar cooking is of global interest. Unfortunately, solar thermal cookers need direct sunlight, so they are only used outdoors. They are inconvenient, being relatively uncontrollable.
 
At the ICREN conference Barcelona Spain April 28 2018, Prof. M. Rezwan Khan of the United International University Bangladesh described how the indirect route of photovoltaic electric cooking is not so crazy after all. He noted, "With an efficiency of 18-19% for commercially available PV panels, using solar PV for cooking (heating) attracts immediate criticism that it is a highly inefficient way of cooking. Although this argument cannot be ignored, solar PV based cooking has its own merits, both technological and economic, if designed and integrated with PV systems properly. With the falling price of the solar PV, it looks more and more attractive to use solar PV as an energy source for clean cooking. To keep the cooking power low, it is important to keep the heat loss at a minimum level. We have shown that insulation of the stove and the pans are important to keep the energy consumption low for cooking. We have also proposed an insulated resting place for the pans after taking off from the stove so that slow cooking may still continue. If the heat loss is contained properly, it is possible to cook with a low power source less than 500W."
 
His slogan is, "Heat does not cook, it is the temperature that cooks" to attract attention to the fact that retaining temperature inside the cooker and the cooking pan is important for energy efficient cooking. A prototype solar e-cooker was designed, fabricated and tested by cooking different foods. An efficiency of 87% has been achieved in the prototype cooker and the water boiling results are presented. Experimental results are presented to show that cooking is possible using much less energy than we usually think. Indeed, his cost analysis showed that such a cooker can be cost effective, costing less than $10 US per month, in off-grid areas if connected to a properly designed Solar Home System.
 
He added, "It is very inexpensive if no battery is used" though this means only cooking in sunshine. As explained in the IDTechEx report, Battery Elimination in Electronics and Electrical Engineering 2018-2028, compromises on specification like this are now commonplace because of the huge gains in cost, life and reliability of equipment from eliminating electrical energy storage. Some mobile desalinators work when the sun is out: storage is now the clean water not the electricity. There are even solar cars that are only needed in daylight so they have no battery. In other cases, such as wireless building controls, no compromise is needed, just multiple energy harvesting and no energy storage. In the case of cooking, battery back-up is useful as the weather may not be sunny all the time or alternatively, the cooking system could have multi-mode harvesting by adding a river or wind turbine. Very low cost "propeller on a string" devices are now available for dangling in the local stream and unfolding hikers wind turbines can be bought for example. For solar alone, Prof. Khan advises, "Integration with a Solar Home System with a proper sizing of the battery keeps the cooking cost within tolerable limits".
 
 
Images UIA
Dr Peter Harrop

Authored By: Dr Peter Harrop

Chairman

Posted on: May 2nd 2018