Paper ovens for the poor

If something that cost £10 suddenly went up to £10,000, we would all start to use cheaper materials, claims chemical engineer Tim Eiloart. A statement of the obvious perhaps. But in a world where raw materials such as wood are becoming increasingly rare through environmental abuse, he has a point. Eiloart’s new project is to […]

If something that cost £10 suddenly went up to £10,000, we would all start to use cheaper materials, claims chemical engineer Tim Eiloart.

A statement of the obvious perhaps. But in a world where raw materials such as wood are becoming increasingly rare through environmental abuse, he has a point.

Eiloart’s new project is to design cheap, solar-powered, paper cookers for the Third World. He argues that cost is relative. In poor countries such as Tanzania it is just as difficult to sell something for £1 as for £100, he says. Technology needs to be tailored to what people can afford.

The cooker is the latest of more than 1,000 different projects undertaken by The Sunseed Trust.

A solar cooker starts with a hemisphere of papier-mache, 72cm across. The size is sufficient to cook a meal for a family of three. A catering size cooker 1m across, big enough for eight people, is also under development. Ideally, the cooker will have a working life up to three years.

A second layer of papier-mache forms the outside wall of the cooker. Between the two is a 5mm insulation layer made from straw, grass, or spots of mud trapping air. A clear polythene cover prevents draughts from cooling the cooker. Like a tiny greenhouse, sun enters the vessel and the infra red energy is trapped inside as heat.

The trick is to keep the cooker as flat as possible so that heat does not rise to the top but is concentrated on the pot which stands on a foil surface, blackened to absorb energy. In Morocco where they bake pitta bread, there is a demand for an extremely flat cooker 4in high, says Eiloart.

A pot of rice takes three hours to cook at 85 95 C. Although slow, the time taken to gather firewood can be offset. And a family-size solar cooker saves the environment half a tonne of wood a year.

Eiloart started the charity in 1982 after quitting Cambridge Consultants which invented, among other things, the Stanley knife and the round teabag. The high-tech international engineering consultancy owes its beginnings to Eiloart, who founded the business in 1960.

He left, he says, because he wanted to help the poor. The Trust’s low-tech mission is to find and spread new ways to help people in poverty on degraded lands.

It has nine staff and up to 25 volunteers who pay £50 to £100 a week each for the experience. Research is carried out in the south-east of Spain which has the driest climate in Europe and is the most akin to desert conditions.

Paper, when converted to papier mache pulp mixed with varnish, dries to a solid which, weight for weight, is stronger than steel in tension and compression. It is, in effect, a composite. Eiloart describes the material as a wet mass of tiny fibres long, thin, hollow tubes which, as they dry out, pull together through capillary action with tremendous force. It can be repaired easily.

For termites, however, papier-mache provides a good meal. Anyone who thinks they can make papier-mache ‘repulsive’ to termites should contact Eiloart. Solutions must be cheap but materials must also be available in the Third World, from local manufacture. For example, instead of polyester which does last longer, the cooker ‘lid’ which captures the sun’s rays is made from polythene film that is produced in poor countries.

The plan is for solar cookers to be made locally by village craftsmen at a target cost of 50p each. An existing design being distributed free by aid workers costs £4 and is made in a factory in California. It would have a vital role sterilising drinking water.

Eiloart is also looking for a better glue. Flour mixed with water in a 1% solution is used to bind the paper. But flaking (delamination) can be a problem.