Efficient Solar Cooker Presented by: Viraj Trivedi CEPT MTM-AM3411

The Problem Half the world’s people must burn wood or dried dung to cook their food. Wood cut for cooking purposes contributes to the 16 million hectares of forest destroyed annually. Half the world’s population is exposed to indoor air pollution, mainly the result of burning solid fuels for cooking and heating. Conventional Solar Cooker don’t work in evening and cloudy weather.

“I’d put my money on the sun and solar energy. What a source of power “I’d put my money on the sun and solar energy. What a source of power! I hope we don’t have to wait ‘til oil and coal run out before we tackle that.” Thomas Edison

Overview Types of cookers Principles of solar cooker design Temperature Cooking time Impact Energy storing materials

Types of solar ovens Box Cooker Panel Cooker Solar Funnel Cooker Parabolic Cooker - not recommended

Box cooker Among easiest and most popular to build and use Lid of a cardboard box reflects light onto pots under glass Advantage of slow, even cooking of large quantities of food

Panel Cooker Sunlight is reflected off of multiple panels onto a pot under a glass lid or in a bag Can be built quickly and at low cost Many different varieties

Solar Funnel Cooker Safe, inexpensive and easy to use Concentrates sunlight into a dark pot in a plastic bag Combines best of parabolic and box cookers Anyone can make one

Parabolic Cooker Highly focused light and high temperatures Cooks nearly as fast as a conventional oven Costly and complicated to make and use – have to turn frequently to follow the sun Potentially hazardous-not recommended

The basic principles - C.A.R.E.S. Collect the light Absorb the light Retain the heat Ease and Efficiency Safety

C: Collect the Light Collect the sunlight using reflectors with an approximately 400 square inch opening (20x20) Easy way to measure: the minimum opening of the cooker needs to be the diameter of an adult’s arm Reflective surface materials include: aluminum, Mylar, aluminized Mylar of any thickness, aluminum or chromium paint (Note: mirror like reflectors can lead to eye damage)

A: Absorb the light Absorb the light – paint the pot matte black or another dark color to absorb the heat Pots can also be elevated by a wire base or posts, allowing the bottom of the pots to collect sunlight

R: Retain the Heat Retain the heat – hot vessels lose their heat to the air quickly so they need to be covered Cover with plastic, glass, Plexiglas, or tempered glass A tight lid will trap steam and speed up cooking Ex: Canning jars work like inexpensive pressure cookers

R: Retain the Heat A note on plastics Oven bags are the best way to retain heat. They are sold in most large U.S. grocery stores, although they may be hard to find in other places (Reynolds© bags work well) If you can’t find oven bags, an alternate solution is transparent High Density Polyethylene bags (HDPE) Prevent the HDPE bags from touching the pots or jars, as they may melt Avoid polyethylene – it melts too easily Good plastic may be the most difficult material to find, and may require extra planning, possibly including importing the oven bags

E: Ease and Efficiency Ease – simplicity of everyday use Funnel and box cookers are the easiest to use – they don’t have to be turned to follow the sun Efficiency - how fast the cooker heats food Parabolic cookers focus light to a point (most efficient) causing dangerous conditions Funnel cookers focus light across a broader area down the center of the cooker (efficient but not dangerous)

S: Safety Safety – Avoid highly focused light such as that in the parabolic cooker. It can damage eyes and start fires Always exercise caution with cookers. Sunglasses are useful when looking into a cooker Cooking pots are hot and should be treated as though they were on a stove-top

Temperatures Sunny Day: heats from 130-145°C (265-300°F) Cloudy Day: heats from 95-105°C (200-220°F) Hot enough to pasteurize water (at least 65-70°C for 20 minutes) Hot enough to fully cook meats, breads, grains, vegetables, etc. Kills disease-causing bacteria

Impact Expect solar ovens to replace 60% of fuel needs in most places The other 40% of the time, due to rough weather or special types of food, traditional methods can still be used Doesn’t replace fire as a way to heat homes

Approximate Cooking Times Vegetables: 1.5 hrs Rice/wheat: 1.5-2 hrs Beans: 2-3 hrs Meats: 1-3 hrs Bread: 1-1.5 hrs

Solar Energy Storing Materials Thermal mass system-  materials with high specific heat capacities such as water, earth and stone. Phase change materials- paraffin wax and Glauber's salt Molten salts Pumped-storage hydroelectricity Natural zeolites Modified Carbon Nanotubes

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