How can you be sure your energy supplier is green?

In the complex area of green energy, not all suppliers are equally green, says Faith Glasgow

Are you one of the many concerned about global climate change and keen to be green - so long as it doesn't take too much time, cost too much money, or involve accosting strangers with collecting boxes? If so, the good news is that it's very simple, and not a great deal more expensive, to switch your electricity supplier to one offering a "Green Tariff" that uses renewable energy, from sources such as wind power, biomass (burning crops or wood), small hydro-electric schemes, landfill gases and solar power.

Are you one of the many concerned about global climate change and keen to be green - so long as it doesn't take too much time, cost too much money, or involve accosting strangers with collecting boxes? If so, the good news is that it's very simple, and not a great deal more expensive, to switch your electricity supplier to one offering a "Green Tariff" that uses renewable energy, from sources such as wind power, biomass (burning crops or wood), small hydro-electric schemes, landfill gases and solar power.

The familiar environmental argument is that, unlike the elderly and inefficient coal-burning power stations, renewable energy sources do not release greenhouse gases into the atmosphere. Furthermore, they help to conserve the earth's limited supply of fossil fuels.

The flip-side for consumers is that smaller scale power stations and environmental soundness are bound to mean higher energy bills. Green tariff prices vary between suppliers, and also according to other factors such as where you live, but Friends of the Earth estimates they cost on average around £50 a year extra on an average family bill in London. Good Energy Ltd (formerly known as Unit[e]) reckons there's a 5-10 per cent premium over energy from conventional sources.

However, the green power scene is a complex area, with green tariffs available both from mainstream regional electricity companies and from specialist eco-suppliers. The trouble is that not all are equally green in practice, and it's not straightforward for consumers to find out the source of the power they are paying for. It could therefore be a mistake, in terms of helping the environment, simply to switch to the first scheme you come across.

So how does it work, and which suppliers are the cleanest and greenest?

Let's be clear, first of all: subscribing to a green tariff does not mean that the electricity coming into your home actually comes from renewable sources. A green supplier will buy some or all of the energy it requires for its customers from small power stations harnessing wind or water power around the country, rather than from the huge stations burning fossil fuel - but it's all fed into the National Grid.

Juliet Davenport, chief executive of Good Energy, explains: "It's all about matching needs, so the green energy we buy matches the amount our customers use over the year. We're like a marketplace - we provide the place for people to bring their power to, and then sell it on to consumers."

In fact, whether or not you request it, suppliers are now obliged by law to buy or generate 3 per cent of green electricity for every unit sold to customers, and that minimum is scheduled to increase to 15 per cent by 2015. In signing up to a green tariff, consumers can boost demand for green energy over and above the government's stipulated level, which in turn means more wind farms, small hydro stations and other innovative technologies will be developed to meet it.

But how can you be sure your energy is green, and, crucially, that it's additional to the green power the supplier has to provide anyway? It's not easy, because although every unit produced comes with a certificate of proof of its green source, companies can trade certificates to meet their quota. "You can request an audit of the product, which will detail where it came from and any other claims about it," suggests Ms Davenport. "It's also worth getting the company's environmental report, which may show, for example, how renewable sources are selected or how it behaves in a wider environmental context."

Friends of the Earth has examined the market carefully and drawn up its own guide to green electricity tariffs. It recommends only those suppliers which sell just green electricity, and which buy a full unit of green electricity for every unit bought by the customers, and which don't sell on all their certificates of proof of greenness. (Reducing the number of certificates in circulation means that other companies have to source some renewable energy themselves, instead of just buying in certificates.)

Only four suppliers get FoE's thumbs up - Eco Energy (from Northern Ireland Electricity), RSPB Energy (from Scottish and Southern Energy plc), and two dedicated green companies, Ecotricity Tariff and Good Energy. Others that fail to make the grade may supply less than a unit of green energy for every unit of electricity bought by customers, or fall down on their certification.

But it's all hideously complicated for weary consumers. "The government position on green energy is under review and we should find out more this summer," explains Ms Davenport. "We want to see real transparency in the market and we are talking to the regulator, Ofgem, about setting up a scheme to try to make it clearer for customers." An ideal solution, she believes, would be for all electricity bills - green or otherwise - to include details of the supplier's power sources.

Northern Ireland Electricity: www.nie.co.uk (NI only)

Scottish & Southern Energy: www.scottish-southern.co.uk

Friends of the Earth: www.foe.co.uk

Good Energy: www.good-energy.co.uk

Ecotricity: www.ecotricity.co.uk

GREEN ENERGY: WHENCE IT COMES, WHAT IT COSTS

* Good Energy

Only sells energy from renewable sources. A quarter of the energy comes from small hydro-electric plants, most of the balance from wind farmsand some from customers who produce electricity from solar panels in their roofs.

* Ecotricity

This supplier owns a number of multiple wind-power generators around the country. It sells on its renewable energy certificates to other companies to help them meet their green energy quota, but it uses the profits to build more wind farms and turbines.

* Eco Energy

This tariff, from Northern Ireland Electricity, allows customers to choose whether some or all of their electricity should be matched by energy from a wind farm in Northern Ireland.

* RSPB Energy

Scottish and Southern Energy pay a donation of £10-£20 to the RSPB's

climate-related schemes if you switch to this option, and a further £5 per year thereafter. All the electricity bought comes from green suppliers.