Octopus Energy, Ecotricity and Good Energy have come top in the latest Which? annual rankings of energy firm green credentials, while E and Outfox the Market finished bottom.

The top three earned the Which? Eco Provider endorsement and scored full marks for buying and selling renewable power and their greenhouse gas emissions.

The consumer champion’s analysis involved asking the providers a series of questions about sustainability practices and their answers were assessed with a points-based scoring system.

Which? also gave points to providers that supplied green gas and offered time of use products (TOU) and above average rates for solar export.

Time of use products charge different rates for electricity at different times of the day or on different days.

Solar export is the process of selling excess electricity generated by solar panels to the national grid. 

Ecotricity and Good Energy have been named Eco Providers for four years in a row while Octopus Energy makes the list for the second year running.

Octopus, which scored 90 per cent, generates renewable power from solar, onshore and offshore wind, and also buys it directly from generators. It has a choice of flexible tariffs as well as one of the more generous rates for solar export. 

The energy provider also installs a range of low-carbon technology for customers and says that it has made it possible for customers to install and run a heat pump for a similar cost to a gas boiler. 

Meanwhile, Ecotricity, which scored 85 per cent, generates electricity from wind and solar power and invests profits into building more renewable generation. It has built 24 wind parks (74 turbines) since 1995 and recently completed two new solar parks.

Ecotricity is one of only four firms that sells green gas (biomethane). Unlike other firms that scored top points, it does not yet offer a solar export tariff. 

Good Energy also scored 85 per cent on the consumer champion’s list of sustainable providers for 2024.

It buys enough electricity from renewable generators to cover all its customers’ usage, matching over 90 per cent of it on a half-hourly basis.

The company buys much of its electricity from small-scale generators which are not supported by government subsidies, meaning it supports generators which might not otherwise exist.

Of the gas the provider sells, 10 per cent is green and its solar export rates are among the more generous. 

Which? included 17 energy suppliers in the assessment. Bottom of the table were E (Gas & Electricity) and Outfox the Market which both scored 0 points.

They do not generate renewable power, sell less of it than average, do not sell green gas, offer no time-of-use products, a below-average rate for exporting solar power, do not install low-carbon measures and could not provide greenhouse gas emissions data.

The other three providers near the bottom of the table were Utility Warehouse, Utilita and Rebel Energy. Utility Warehouse scored 15 per cent. All of its points were earned in the consumer champion’s greenhouse gas emissions section. 

Meanwhile, Utilita was joint-fourth from the bottom, gaining points for TOU and solar export products, for low carbon installations and greenhouse gas emissions. It scored a total of 35 per cent, the same as Rebel Energy.

Rebel Energy got four points (out of seven) for buying and selling renewable power and three points for its greenhouse gas emissions.

Ultimately, the most impactful way for households to cut their carbon footprint is to use less gas and electricity.

Consumers can use Which?’s new home energy planning service to explore the money-saving efficiency improvements they could make.

Emily Seymour, Which? Energy Editor, said: “We know from our research that many consumers want to make sustainable choices and play their part in reducing carbon emissions. 

“Which? research shows some energy firms are doing much more than others when it comes to sustainability - with the top-ranked providers leading the way in areas like generating renewable power and helping customers cut their greenhouse gas emissions.

“Choosing one of Which?’s Eco Providers offers reassurance that your energy supplier has impressive green credentials. You can also use Which?’s new home energy planning service to explore the improvements you could make to cut your own carbon footprint and make your home warmer and more energy efficient this winter.”