By Richard Black
Environment correspondent, BBC News website
At the heart of the idea is a simple black painted box...
A cheap solar cooker has won first prize in a contest for green ideas.
The Kyoto Box is made from cardboard and can be used for sterilising water or boiling or baking food.
The Kenyan-based inventor hopes it can make solar cooking widespread in the developing world, supplanting the use of wood which is driving deforestation.
Other finalists in the $75,000 (£51,000) competition included a device for streamlining lorries, and a ceiling tile that cools hot rooms.
Organised by Forum for the Future, the sustainable development charity founded by Jonathan Porritt, the competition aims to support concepts that have "moved off the drawing board and demonstrated their feasibility" for reducing greenhouse gas emissions, but have not gained corporate backing.
"The Kyoto Box has the potential to transform millions of lives and is a model of scalable, sustainable innovation," said Peter Madden, the forum's chief executive.
It is made from two cardboard boxes, which use reflective foil and black paint to maximise absorption of solar energy.
Covering the cooking pot with a transparent cover retains heat and water, and temperatures inside the pot can reach at least 80C.
As many as two billion people in the world use firewood as their primary fuel.
The idea of cooking using the Sun's rays has been around for centuries, and a number of organisations including Solar Cookers International are already supporting their manufacture and distribution in the developing world.
Reducing reliance on firewood reduces deforestation, but also improves the health and wellbeing of villagers who do not have to trek for miles collecting the increasingly scarce wood nor spend hours inhaling wood smoke, a major cause of respiratory disease.
What impressed the judges about the Kyoto Box was the potential for production to be scaled up significantly in a number of developing countries.
"It's really the mass manufacturing aspect," said Jon Bohmer, who founded the company Kyoto Energy in Kenya.
"We can take existing factories like cardboard factories and begin to make thousands and thousands of the cookers each month," he told BBC News.
"So far, solar cooking has been a DIY project with people making them on their own in slums and so on; but this could be the Volkswagen, you might say."
An evaporating tile was another of the competition's finalists
Mr Bohmer hopes to gain funding from the international carbon market.
By demonstrating that using the Kyoto Box reduces greenhouse gas emissions, he can gain "carbon credits" from western countries and companies.
"With as many people as there are in the developing world today, they can't just cook using trees - they'll finish off all the trees," he said.
Other innovations reaching the competition's final included
- a feed additive for livestock, derived from garlic, which can cut methane emissions from cows and sheep by at least 5%
- an indoor cooling system that uses a building's exhaust air to evaporate water held inside hollow tiles
- a giant microwave oven that turns wood into charcoal
- an aerodynamic cover for lorry wheels that reduces drag and thus fuel use
The Climate Change Challenge competition was also supported by the Financial Times newspaper and technology company HP.