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Parabolic Solar Reflector and Heat Storage Cooker


Table of Contents

Boiling Point
Front cover of Boiling Point issue 36
Issue 36 (1995) Solar Energy in the Home
ArticleParabolic Solar Reflector and Heat Storage Cooker
AuthorGerhard Jobst


[top] [end]Effective solar cooking

Gaining and retaining the sun's power for cooking - these are the two principles that can generally be employed by solar cookers.

While box-type solar cookers try to use both principles at the same time, the use of one or more haybox cookers together with a powerful parabolic type cooker makes a brilliant combination.

[top] [end]The SK 12 parabolic solar reflector

This is a high-capacity solar cooker. The size and design of its cooking pots are especially adapted for haybox cooking. Once in the haybox the food is cooked further by the retained heat. It can be left unattended and keeps warm for later consumption while the cooker can immediately be used for other cooking or sterilizing water.

[top] [end]Manufacture

Manufacture of the SK 12 is possible by local craft workers using simple cutting, bending and punching tools and utilizing easily available materials throughout, such as strip steel, wire and ordinary nuts and bolts.

With its 1.4 metre diameter mirror the SK 12 is a powerful solar collector, capable of bringing three litres of water to the boil within half an hour, as well as allowing frying. So it is a high-heat cooker, and together with cooking pots of 28 cm in diameter, ie pots of up to 10 litres, it is also a high-capacity cooker which can meet the cooking needs of up to 20 people.

[top] [end]Traditional cooking

'Sitting by the fireside, waiting for the meal to be ready after a hard day's work...' Everybody knows that the family's traditional fireside has more significance than just cooking. Unfortunately only a few are aware of the fact that fuel-saving solar cooking can blend perfectly with fireside traditions if only a simple and comfortable system of ancient origin is used.

[top] [end]Back to our roots

Daily cooking frequently includes a long simmering period which is required for many beans, grains, stews and soups. The amount of fuel needed to complete these cooking processes can be greatly reduced by cooking with retained heat in a heat storage cooker such as a hay box.

[top] [end]The haybox

The haybox is simply a well insulated box or basket lined with a reflective material into which a pot of food previously brought to the boil is placed. The insulation greatly slows the loss of conductive heat, convective heat in the surrounding air is trapped inside the box, and the shiny lining reflects the radiant heat back into the pot.

The food is cooked in one to two hours by the heat retained in the insulated box. This works best when the pot fits snugly into the insulation with no air in between.

[top] [end]Be inventive

Such a box or a basket can easily be made of inexpensive, locally available materials. It can be wooden, or a can-in-a-can, or card board, or any combination. Hay, straw, rushes, feathers, sawdust, rags, wool, shredded paper, etc are all good insulating materials.

Comparison of some normal and parabolic/haybox cooking times
Food Normal cooking times SK 12 Cooking time + time in the haybox
Rice 60 minutes 12 + 55 = 67 minutes
Beetroot 90 minutes 25 + 70 = 95 minutes
Stewed meat 70 minutes 25 + 50 = 75 minutes
Potatoes 45 minutes 20 + 40 = 60 minutes

Principles to be kept in mind are:
  • the insulation should cover all six sides of the box;
  • the box should be airtight;
  • the inner surfaces of the box should be of a heat reflective material such as aluminium foil.

After the food is cooked it keeps hot for many hours.

[top] [end]Haybox cooking is different

There are some adjustments involved in cooking with haybox cookers:
  • less water should be used since it is not boiled away;
  • less spicing is needed since the aroma is not boiled away;
  • cooking must be started earlier to give the food enough time to cook at a lower temperature than on the solar cooker or over the fire;
  • the food should boil for several minutes before being placed in the box. This ensures that all the food is at boiling temperature, not just the water,
  • haybox cookers work best for large quantities (over four litres) as small amounts of food have less thermal mass and cool faster than larger quantities.

[top] [end]Contents: Boiling Point 36: Solar Energy in the Home

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Parameters for a Solar Cooker Programme - The Sunstove Solar Box Cooker - Sunstoves in the Republic of South Africa - Gaining Ground in Solar Box Cooking in Kenya - Solar Cookers - A Cause Worth Promoting - Free Energy from the Sun - A Solar Box Cooker with a Reflecting Lining - The Solar Puddle - A New Water Pasteurization Technique - Renewable Energy - A World Bank View - ESMAP study points toward village-level management of woodfuel resources in Chad - Burning Charcoal Issues - A Dangerous Trade - Saving Wood by Burning Coal - Haitis Domestic Fuel Project - Coal briquetting and clays for Zambian stoves - Improving the three-stone fire - Comparative tests of solar box cookers - Parabolic Solar Reflector and Heat Storage Cooker - An Affordable Parabolic Solar Cooker



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