A number of bases inside the US have begun to tap into renewable fuel sources including wind and solar energy.
In Montana, Hawaii and Minnesota all petrol must contain 10% ethanol, while Washington state requires petrol and diesel to contain 2% renewable fuel by volume.
On pain of fines, But with the carrot of subsidies, these require that a certain amount of renewable fuel be blended into petroleum-based fuels over the next decade or so.
The UK is trying to remove aviation from the bloc's target on renewable fuels.
But she said an equally important use for the renewable fuels would be to store solar energy so it is available at times of peak demand, and overnight.
Scientists have adapted a process called "gasification" which is already used to clean up dirty materials before they are used to generate electricity or to make renewable fuels.
Friends of the Earth, for example, says the efficiency of stoves is irrelevant if they burn renewable fuels such as dung or wood, as those in poor countries often do.
