Q&A: Farm waste in your tank

A Canadian company is getting a multimillion pound investment from Shell which could see UK drivers putting a petrol-bioethanol blend in their tanks in future years. BBC environment correspondent Tim Hirsch looks at the pros and cons of biofuels.

How is this fuel made?

A process converts waste plant material such as wood and straw into sugar, which is then fermented and distilled into a type of alcohol that can be used as fuel.

Why has it been developed?

It has the combined advantages of cleaning up emissions from engines, reducing our dependence on oil and providing farmers with an extra source of income.

What are the environmental benefits, and are there any disadvantages?

Bioethanol produces much less of the gas carbon dioxide, which is one of the principal contributors to the human-induced greenhouse effect, the process linked by many scientists to the accelerated warming of the Earth's atmosphere. The plant material used to make the new fuel absorbs carbon dioxide from the atmosphere as it grows, and also emits slightly less of the gas from the tailpipe when the bioethanol is burned.

Up until now, the principal disadvantage has been cost, but the process now being developed in Canada makes it possible to make ethanol using much less energy - and therefore more cheaply.

Can conventional vehicles use the fuel without problems?

Up to a point. Car manufacturers currently guarantee that a mixture of 10% ethanol to 90% petrol can be put into ordinary engines without affecting performance. This is already widely done in countries including the United States and Brazil. If the ratio of ethanol is increased, adjustments have to be made.

Is bioethanol an alternative to new technologies such as hydrogen fuel cells?

A moot point. Supporters of biofuels say that with the right incentives, they can make a big contribution in the very near future to cutting emissions from vehicles, whereas few expect hydrogen fuel cells to be commercially viable for at least a decade, and probably longer.

However once hydrogen does become viable, it has the great potential of producing no emissions other than water, whereas bioethanol still creates some pollution.

Is the UK Government doing anything to encourage the use of bioethanol?

Gordon Brown announced in this year's budget that biofuels such as ethanol and biodiesel (made from oilseed rape crops) would attract 20p less duty per litre than standard fuels, but there's been criticism from farming groups that this discount should be much greater if these fuels are to make a real contribution to the fight against man-made climate change.