The first supermarket powered by tomatoes

Waitrose's Rickmansworth store uses electricity created as a byproduct of warming the large greenhouses needed to grow tomato plants.

Two farms, in Chichester and Stansted, each use a gas-powered turbine engine to heat their greenhouses. Normally, this heat escapes but in this case it powers a second turbine, which feeds electricity directly into the National Grid.

The process also creates carbon dioxide, which is absorbed by the tomato plants to help them grow. Bill Wright, Waitrose's energy and environment manager, said: "For us tomato power is the perfect virtuous circle - farmers get CO2 to use in the ripening process and Waitrose gets an environmentally friendly form of power for our shop."

Despite using gas to power the turbines, Waitrose estimates the system saves around 1,000 tonnes of CO2 each year. "We hope this can be rolled out across more stores," said Mr Wright.

"We have several other tomato growers interested in the system. We are also investing heavily in wind and solar energy and are willing to look at any new technology that comes along."

The gas is bought from electricity company Green Energy.

Chief executive Doug Stewart said: "Electricity from growing tomatoes is extremely positive because it has multiple benefits and no waste - all the heat is used for warming the greenhousesthe CO2 is 'fed' to the plants and the electricity goes to consumers and businesses who want green power. The gas we use to power the initial turbine is also as green as we can make it."

The two companies are working on a second system that is entirely green with gas coming from decaying pigswill and vegetable matter. "We hope to begin using it soon," said Mr Stewart.

Once in the National Grid system, the green electricity travels about 70 miles from Chichester and 50 miles from Stansted. Green Energy is licensed to use the National Grid.