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Updated: 19 Apr 2022

Differences between green energy suppliers

Energy companies take different approaches to selling renewable energy - find out which is best for you.
Sarah Ingrams

Around 60% of energy companies only sell tariffs with 100% renewable electricity, and around 60% of customers are with those firms, according to a report from energy consultancy Cornwall Insight, commissioned by Which? (published in June 2021).

But companies have different approaches to providing their renewable electricity. So if you have a clear idea of what you want from a green tariff, check carefully that you’ll get what you're after – it’s not always easy to tell at a glance. 

In October 2021, we asked more than 40 energy companies to tell us specifics about the green electricity and gas they sell to homes, and 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 made Good Energy our first Eco Provider for energy.

Can I get 100% renewable electricity to my home?

Electricity pylons with trees and houses

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. On average, our electricity is 40% from renewable sources. This is the standard fuel mix of the National Grid. 

Average UK fuel mix

  1. Renewables - 40.3%
  2. Natural gas - 38.2%
  3. Nuclear - 16.1%
  4. Coal - 2.7%
  5. Other fuels - 2.7%

Source: Department for Business, Energy and Industrial Strategy's UK fuel mix, for 1 April 2020 to 31 March 2021. 

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?

Pouring boiling water from an electric kettle

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

It’s not clear to customers either – when we asked more than 3,600 people to choose from a list of definitions for renewable energy tariffs, a third said that they didn’t know*.

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.

Signing a contract

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.

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

Woman looking confused comparing green energy tariffs

There are four 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 our 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?

REGO certificates cost just £1.45 per customer per year in 2020, according to consultancy Baringa. Prices have risen since January 2021 but they're still relatively cheap. 

So it doesn’t cost an energy company very much to be able to say it sells renewable electricity. That’s how some of the cheapest tariffs on sale in the past offered '100% renewable electricity'.

However, Cornwall Insight says that REGOs ‘do not represent an investible revenue stream for the generating party’. 

It tends to cost more to buy 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.

But with energy prices rising since autumn 2021, cheap deals are few and far between.

Two employees in high-vis working at a wind turbine

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. These companies are:

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

Some companies let you ‘top-up’ your tariff, which essentially means you pay more for additional green features. This could be increasing the proportion of renewable electricity you pay for or adding green gas or carbon offset.

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

Coal-fired power station

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 a Guarantee of Origin - GoO) certificates are and how it uses them?
  • Does the company have direct links to fossil fuels? Some energy firms generate renewable power and also own gas power stations or invest in oil.

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

Even so, it’s often hard to tell what a company is really doing to support renewable electricity. So, in July and August 2021, we asked 49 energy suppliers to tell us exactly how they sourced their renewable electricity. 

Read our energy company reviews to find out which suppliers generate renewable power, which buy it directly from renewable sources, and which simply purchase certificates. 

Other sustainable features of energy companies

Woman planting tree saplings

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 time-of-use tariffs 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.

*Online survey of 3,622 members of the general public in September 2020.