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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.
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See moreThe 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.
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.
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:
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:
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.
There are several different approaches that energy companies take to providing '100% renewable' electricity tariffs. These are:
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.
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:
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.
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:
Don’t be swayed by environmentally friendly images, designs and phrases if they’re not backed-up with factual information.
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.
Overall % score | Total score (max 20) | Generating renewable power (max 4) | Buying and selling renewable power (max 7) | Generates or buys directly carbon-intense power (max 0) | Sells green gas (max 2) | TOU and SEG rate tariffs (max 2) | Low carbon installations (max 2) | Transparency and clarity (max 3) | |
Good Energy (Eco Provider) | 80% | 16 | 0 | 7 | 0 | 2 | 2 | 2 | 3 |
Octopus Energy* (Eco Provider) | 80% | 16 | 3 | 6 | 0 | 0 | 2 | 2 | 3 |
100 Green (Eco Provider) | 70% | 14 | 0 | 7 | 0 | 2 | 2 | 0 | 3 |
Ecotricity (Eco Provider) | 70% | 14 | 3 | 6 | 0 | 1 | 0 | 1 | 3 |
British Gas** | 70% | 14 | 2 | 4 | 0 | 1 | 2 | 2 | 3 |
Co-op Energy | 65% | 13 | 2 | 6 | 0 | 0 | 0 | 2 | 3 |
Ovo Energy | 60% | 12 | 0 | 5 | 0 | 1 | 1 | 2 | 3 |
*Octopus Energy also supplies Affect Energy, Ebico Living and London Power customers. Ebico Living and London Power customers cannot access its TOU or SEG tariffs.
**British Gas is not an Eco Provider because its parent company, Centrica, has a direct relationship with fossil fuels.
***E.ON Next initially told us it did not generate renewable electricity. However after Which? shared its press release it said that it does actually owns two biomass CHPs (one in Lockerbie and one in Sheffield) as well as a geothermal energy centre in the city of London. E.ON Next also supplies Sainsbury's Energy customers.
Information correct August 2023.
Points were awarded based on the companies' responses, and on information published on their websites, including the annual Fuel Mix Disclosure (FMD).
Besides 100% renewable electricity and green gas, companies have other approaches to improving their sustainability including: