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The Sunstove Solar Box Cooker

Boiling Point
Front cover of Boiling Point issue 36
Issue 36 (1995) Solar Energy in the Home
ArticleThe Sunstove Solar Box Cooker
AuthorRichard C Wareham
In the past two years approximately 1,500 Sunstoves have gone out into South Africa and surrounding countries. Figure 1 shows three types of cooker; the one on the right was our first plastic design and was distributed mainly via the Girl Guides Association. This model worked well, and about 900 were sold, but the plastic outer case, only being stapled together, did not stand up well to transport handling.

Therefore we have changed to the centre model in the picture which has a blow-moulded outer shell and is altogether more rugged. To date, more than 600 have been sold. We are trying to keep it affordable for the people who need it the most, and are a non-profit organization. Nevertheless, it may still be out of reach of many people.

Because of this, and hopefully to attract funding for the project, we have designed the model on the left of the photograph which we call our Job-creation unit. This can be made in small communities without expensive equipment. Whether it can be made more cheaply remains to be seen.

Since the 1940s hundreds of different solar cooking units have been designed and tested. The goal was to reduce the traditional use of wood by cooking with solar energy. Most designs failed because - of high cost, short life, scarce materials, assembly problems, difficulty of use, lack of training, high freight costs and duties, etc.
Figure 1: Three types of Sunstove solar cookers
Figure 1: Three types of Sunstove solar cookers
The challenge was to design and build a simple, affordable unit that developed the temperature needed to cook the local foods. Education and training was also needed to gain social acceptance.

The most expensive part of a solar cooker has been the external flat or parabolic reflectors, which become ineffective due to gradual loss of reflectivity, destruction by the wind, and lack of adjustment or focusing. This has made solar cookers without external reflectors the most desirable.

It was interesting that the cost of US$65.00 for material and labour for solar cookers made in Pakistan is the same as the wooden box units being built by several groups in Kenya. This is typical for 'home-made' units. The Sunstove cost in South Africa is US$22.00, including materials, labour, administration, overheads and amortization of moulds and tooling (excluding VAT). We will start manufacturing Sunstoves in the USA for the Caribbean islands and surrounding countries this year. The Minneapolis Foundation will use plastic re-grind for the case and scrap aluminium for the interior which reduces the cost.

[top] [end]Sunstove design, specifications and capabilities

The Sunstove is a practical solar cooker:
  • affordable
  • easy to use
  • no reflectors
  • Iightweight
  • weather resistant.

Its sides were 'winged' out to increase the solar collecting area and to reduce the internal volume to be heated. The sloped internal walls of this 'hot box' reflect, radiate and conduct the sun's energy to the black cooking pots. This creates the effect of an 'enclosed parabolic' cooker that reduces the losses caused by oxidation or stain on the reflectors. Aluminium coloured interior walls are recommended but black metal walls only increase the cooking time by a maximum of 10 per cent. A transparent plastic cover retains the heat absorbed by the black pots.

The Sunstove has an area sufficient to collect the solar energy needed to cook six to eight litres of food. The internal dimensions will accommodate two cooking pots, one six litre and one two litre. The plastic cover is sloped to collect and direct the sun's energy to the black pots thus increasing the temperature and decreasing the cooking time.

The Sunstove rapidly reaches cooking temperatures as high as 125°C and will easily pasteurize water or milk. Cooking time will vary according to local conditions, i.e. hours of sunshine, quantity and type of food, time of day, latitude, etc.
The Sunstove 'Point it towards the sun and enjoy your food!
The Sunstove 'Point it towards the sun and enjoy your food!
Overloading the cookers with food can increase the heat and time required for cooking past the capabilities of the unit. The cooker needs to be protected from wind and animals.

'Point it toward the sun and enjoy your food!'

NOTE: The Sunstove was designed for mass production.

Tooling was purchased in 1992 in Africa and production of the Sun- stove started in 1993. Labour, materials and overheads cost under US$25.00 per unit.

[top] [end]General Information

  • Black pots with a cover and no plastic handles.
  • Small pots for small quantities.
  • Start cooking when you can see your shadow.
  • Best cooking between 10.00 am and 3.00 pm.
  • Stir only when absolutely necessary.
  • Stirring cools the food and slows the cooking.
  • The Sunstove will cook when the sun shines for more than 30 minutes each hour.
  • When the sun does not shine, use the wood you saved when the sun did shine.

The Sunstove is designed to cook for a family of six. That is one pot holding 20 cups (five litres) of your basic food plus a small pot with one to two litres (four to eight cups) of vegetables, stew or dip. Each litre of food will take from half to one hour to cook.

Point it towards the sun. For maximum heat and energy adjust to the sun every two hours. Place the Sunstove in an area protected from the wind and animals.

[top] [end]Typical cooking times

Vegetables, potatoes, mealie meal, rice, millet, chicken pieces, fish take up to three hours.

Meats, dried peas and beans, large portions of food take up to four hours.

[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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Page created: 16 August 2007; Last edited: 05 September 2008; Version: 2
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