Food waste to provide green gas for carbon-conscious consumers

Biogas sourced from food waste and sewage is to piped into British homes under a new 'green gas' tariff

Rotting leftovers, wilted salad and even sewage are to provide a new source of "green gas" to heat our homes.

From today, British householders will be able to register for Ecotricity's new tariff to buy green gas – commonly known as biogas – as a way of reducing their carbon footprint and cutting landfill waste. It will be a first for carbon-conscious consumers who have previously only been able to buy "green electricity" from suppliers.

Britain discards about 18 million tonnes of food waste a year, which Ecotricity said could generate enough biogas to heat 700,000 homes. The Conservative Party believes 50% of the UK's natural gas supply could be replaced by biogas .

Dale Vince, the company's founder, said: "We're the real British Gas now. We're kickstarting the market to move Britain from brown to green gas." He said natural gas sourced from countries such as Russia was expected to run out in 15-20 years.

Householders who sign up to Ecotricity's deal will be supplied from January, although initially their gas will come from conventional "brown" natural gas – a percentage of biogas will only be injected into the national grid later in the year. The company, which currently has about 30,000 electricity customers, said it wanted to eventually source 50% of its gas tariff from biogas and would match British Gas on dual-fuel pricing. Vince said he planned to invest about £50m to build two "green gas mills" to make the biogas, but would also look at buying in biogas from other sources, including suppliers in Holland.

Audrey Gallacher, energy expert for the government watchdog Consumer Focus, said she welcomed the idea, but warned that confusion could arise over what the green tariff will initially provide: "Green gas tariffs could be good news for customers who want to buy environmentally friendly energy. However, it must be made clear to any customer signing up that they are investing in creating a demand and supply of energy-efficient fuel for the future."

Biogas is generated in anaerobic digesters, where organic material is fed into tanks where microbes break down the material without oxygen and release methane and carbon dioxide, the main elements of biogas. The biogas can then be used to make electricity or, as Ecotricity plans, processed and injected into the pipes of the national gas network.

The raw material for digesters can come from a variety of sources, including food waste, sewage and farm waste, although Vince ruled out the latter. "We'd probably avoid agriculture waste because we don't want to support factory farming, and a properly run organic farm won't produce excess slurry," he said.

The National Grid said there was no technical reason why Ecotricity's plan wouldn't work and added that it supported using renewable gas to hit carbon-cutting targets. Extra momentum for UK biogas should arrive in 2011, when the government is due to introduce a renewable heat incentive, giving financial assistance to generators of heat from renewable sources, from householders using ground-source heat pumps to companies such as Ecotricity.