Differences between green energy suppliers

Energy companies that offer tariffs with 100% renewable electricity have different approaches to providing it. 

In August 2023, Which? asked UK energy companies to tell us the specifics about the green electricity and gas they sell to homes, as well as other sustainable practices.

We also looked at their websites to see how easy it is for customers to understand what they’re buying and uncover which energy supplier is the greenest. 

As a result, we named 100Green (previously known as GEUK), Ecotricity,  Good Energy and Octopus Energy our Eco Providers for energy for 2023.

All four only sell 100% renewable electricity. 

Can I get 100% renewable electricity to my home?

The source of the electricity that comes by wires to your home at any moment depends on where you live and how much renewable generation is happening across the country at the time. Around 40% of our electricity comes from renewable sources on average.

Average UK fuel mix

1. Renewables - 40.8%
2. Natural gas - 39.3%
3. Nuclear - 13.9%
4. Coal - 3.4%
5. Other fuels - 2.6%

Source: Department for Energy Security and Net Zero's UK fuel mix, for between April 2022 and March 2023.

If you buy a 100% renewable tariff, it does not change the electricity that comes into your home. But it does change what part of the energy market you are paying for.

If you’d like to start generating your own renewable electricity, find out more about solar panels and home energy storage.

What are the rules for renewable energy tariffs?

There is no set definition of what a renewable or green tariff is, and companies take a variety of approaches. 

To make an ‘environmental claim’ about a tariff, an energy company must:

• Show that the environmental gain is because the customer chose the tariff;
• Publish its fuel mix and information about the environmental benefit of the tariff;
• Be able to prove where its renewable energy has come from, by having enough certificates.

To sell a tariff labelled as 100% renewable electricity, an energy firm must buy enough certificates for renewable energy to match what customers on the tariff use over a year.

If a company has bought enough certificates to match all of its customers’ electricity use (on all tariffs), it will be able to say that its overall fuel mix is 100% renewable. These certificates prove that a megawatt hour of renewable electricity has been generated. There are two types:

• Renewable Energy Guarantees of Origin (REGO) if they’re for electricity generated in the UK
• Guarantees of Origin (GoOs) if they’re for electricity generated in the EU (these won't be valid for 2023-24 fuel mixes).

But these certificates don’t prove that the company has generated any renewable electricity itself, nor bought renewable electricity directly from a generator. Providers can buy them without buying the associated renewable electricity.

Different approaches to renewable energy tariffs

There are several different approaches that energy companies take to providing '100% renewable' electricity tariffs. These are:

• Providing renewable power from generators the company operates to meet customer demand;
• Helping customers to buy stakes in renewable generation and matching their consumption to the output (e.g. a customer buys a stake in a wind farm) – this is rare;
• Having a contract or trading deal to take the output of a renewable generator and incorporate it into a tariff;
• Matching customer consumption against renewable output via traded certificates (e.g. Renewable Energy Guarantees of Origin - REGOs).

Many companies use a combination of these, and firms can buy certificates separately from the renewable power. 

The Committee on Climate Change explained that the ability to 'unbundle' REGOs from the power generated 'could mean that the supplier of the green tariff is not actually purchasing renewable electricity but it is simply purchasing the certificate'.

Find out whether your energy company generates renewable electricity, buys it directly from generators or buys renewable energy certificates only with our energy company reviews.

Does green energy cost more?

Energy consultancy Cornwall Insight suggests REGO certificates cost £11.28 in 2022 for the average household bill. 

This is much more than they cost a few years ago. However it doesn't cost a huge amount for an energy company to be able to say it sells renewable electricity. which is how some of the cheapest tariffs on sale in the past offered '100% renewable electricity'.

It tends to cost more to buy your energy from companies that have more direct links to renewable generation. For example, buying renewable electricity directly from a generator on a long-term contract can provide guaranteed revenue and a route to market for the power without the costs of trading on the wholesale market, explains consultancy Baringa.

Many renewable generators receive government subsidies. Some energy firms buy from generators which don't have subsidies, such as smaller generators. This means that they're helping support renewable projects that might not otherwise exist. This can come at an extra cost.

Three energy companies were given exemptions from the price cap on default energy tariffs because they proved to energy regulator Ofgem that they have higher costs because they support renewables, that they support renewables beyond existing subsidies, and that customers have actively chosen to buy them. 

All three applied to Ofgem to be allowed to charge more and their tariffs are typically among the priciest available. 

These companies are:

• 100Green
• Ecotricity
• Good Energy

However with energy prices still high, it's hard to find tariffs that are much cheaper than the price cap. 

Understand the energy price cap and what it means for your bills.

How do you tell if you’re picking a truly green energy company?

Since there is no set definition of what a green or renewable tariff is, it can be tricky to tell. First, be clear about what you want or expect from the company you buy from. Then, look out for the following to help you:

• Does the company say it owns renewable generation, such as solar or wind farms?
• Can you tell if the company buys power (as well as certificates) from generators? Sometimes you’ll be able to find a section where the company asks generators to get in touch about selling power to it.
• Is there a clear explanation of how the company proves that the electricity it sells is 100% renewable? 
• Does the company explain what REGO (or Guarantee of Origin - GoO) certificates are and how it uses them?

Don’t be swayed by environmentally friendly images, designs and phrases if they’re not backed-up with factual information.

Which? Eco Providers for Energy 2023

It’s often hard to tell what a company is really doing behind the scenes to support renewable energy. So, in August 2023, we asked energy suppliers in Great Britain to tell us exactly how they sourced their renewable energy and assessed their transparency and clarity. We found four companies that stood out. 

These are 100Green, Ecotricity, Good Energy and Octopus Energy. 

All scored close to full marks for buying and selling renewable power and also scored highly for generating renewable power or selling green gas.

British Gas missed out because its parent company, Centrica, has a direct relationship with fossil fuels.

Co-op Energy also missed out. However it still scored well for buying and selling renewable power.

The table below details the results of our findings. Swipe or scroll right to see the total score breakdown in full.

How we score energy supplier sustainability

Points were awarded based on the companies' responses, and on information published on their websites, including the annual Fuel Mix Disclosure (FMD).

• Generating renewable power: Points were awarded to those that generate renewable electricity, more where it accounted for a greater proportion of their customers' use. 
• Buying and selling renewable power: Companies were awarded points for buying renewable power directly from generators through PPAs or similar contract arrangements, and additional points according to the percentage of customer supply this accounted for and whether it was from generators which did not receive government subsidies. Companies also gained points for supplying a greater percentage of renewable energy than the fuel mix average, and another point for supplying 100% renewable electricity. A point was deducted for power backed by GoO certifications (which support non-UK produced renewable power). 
• Carbon intense power: Points were deducted for generating electricity from fossil fuels or buying directly from fossil-fuel generators. 
• Green gas: We gave a point for selling green gas, and another one if it it made up more than 5% of gas sold. 
• Time of use (TOU) and SEG (Smart Export Guarantee) tariffs: Firms recieved a point if they offered one or more ToU tariffs. These encourage customers to use energy at less popular times which is when the National Grid has most renewable energy in its mix. We awarded a point to suppliers that had above average SEG rates for domestic generators, such as those with solar panels installed. We calculated this based on responses received.
• Low carbon installations: Suppliers earned points for providing customers with ways to reduce their home's carbon footprint by installing heat pumps, solar panels, battery storage and insulation. 
• Transparency and clarity: Points were awarded for websites with clear, easily-findable information about how their renewable electricity is sourced. Also for sharing with Which? a breakdown of their greenhouse gas emissions data.

Other sustainable features of energy companies

Besides 100% renewable electricity and green gas, companies have other approaches to improving their sustainability including:

• Sustainable accreditation, such as Bcorp or Vegan Society
• Encouraging sustainable behaviour through apps, schemes or including smart thermostats in their tariffs
• Making charitable donations
• Participating in community or charity energy programmes (such as involvement with solar panel community projects)
• Tree-planting.