What a Green Tariff Actually Buys
The residual mix, beside the average
The residual mix is the electricity left after renewable certificates have been claimed by suppliers. It is the mix assigned to supply with no green claim. The chart compares it with the national average.
Disclosure period 2025/26 · 1 Apr 2025 to 31 Mar 2026
What the electricity nobody claimed is actually made of
Across the United Kingdom, electricity supplied over this period was counted as 48.0% renewable. Once every renewable certificate had been allocated to a supplier selling a green tariff, what was left for everybody else in Great Britain was 10.8% renewable. That leftover is the residual mix, and it is what your electricity is counted as if your supplier makes no green claim.
| Fuel | Residual mixGB · no green claim | EveryoneUK average | Difference |
|---|---|---|---|
| Natural gas | 65.3% | 31.4% | +33.9 pts |
| Coal | 11.4% | 4.7% | +6.7 pts |
| Renewables | 10.8% | 48.0% | −37.2 pts |
| Nuclear | 7.1% | 13.7% | −6.6 pts |
| Other fuels | 5.4% | 2.2% | +3.2 pts |
The residual mix covers GB because Fuel Mix Disclosure is a Great Britain supply licence condition; the average covers the UK. Part of the difference between the columns is that change of boundary, not only the certificate accounting.
Carbon intensity by fuel
Averaged over everything the United Kingdom generated, 147 grams of CO₂ per kilowatt hour in 2025. These are generation emissions only — not the fuel supply chain, and not imports.
- Other fuels969 g/kWh
- Coal2024 figure — none published for this year921 g/kWh
- Natural gas365 g/kWh
- Nuclear0 g/kWh
- Renewables0 g/kWh
Where a fuel shows an earlier year, the publisher gave no figure for this one — for coal, because no coal-fired electricity was generated in the United Kingdom at all — and directs that the earlier value be used. It is shown with the year it belongs to rather than restated as this year’s.
- Transmission and distribution losses 2025/26
- ×1.1098
- Every kilowatt hour that reaches a meter needs about 11% more generated, because that much is lost in the wires on the way.
- High-level radioactive waste
- 0.006 g/kWh
- Published alongside the carbon figures, across all United Kingdom generation rather than nuclear alone.
This is not the generation mix published in DUKES or Energy Trends. It is compiled on an attribute basis, over electricity supplied rather than generated, with imports allocated using the European Attribute Mix — so it is a different measurement of the same year and the two will not agree.
DESNZ replaces this table each August rather than adding to it, so only the current disclosure period is published. This page will build a history from 2025/26 onwards as each new period lands.
Contains public sector information licensed under the Open Government Licence v3.0 Fuel mix disclosure data table · Open Government Licence v3.0
How a certificate makes electricity green
Each megawatt hour of eligible renewable generation earns a Renewable Energy Guarantee of Origin (REGO). A supplier can redeem enough REGOs to cover customer use and describe that supply as renewable. The certificates can be bought separately from the electricity.
This means two tariffs can carry the same renewable label while one is backed by owned generation or long-term contracts and the other by separately bought certificates.
Ofgem publishes who redeemed certificates and when. See who redeems Britain’s renewable certificates for the latest register figures.
What this does and does not tell you
The residual mix does not describe the electricity physically reaching a home. It shows how unclaimed electricity is accounted for. If the backing of a tariff matters to you, ask whether the supplier owns generation or has long-term contracts with named projects.
To use electricity when the forecast grid mix is cleaner, see when to use electricity in your region.
Why this disagrees with the generation mix
The residual mix is an accounting measure for electricity supplied and includes imports using the European Attribute Mix. Generation data measures what British power stations produced, so the percentages will not match. This is also why coal can appear in the residual mix when no British coal station generated electricity.
For what was physically on the grid, see Britain’s electricity right now.
Frequently asked questions
What is the residual fuel mix?
It is the fuel mix assigned to every unit of electricity that no supplier has claimed as renewable. Suppliers selling green tariffs retire renewable certificates covering their customers’ usage, and those units are removed from the national pool. The residual mix is what is left in the pool afterwards, and it is the mix your supply is counted as if your tariff makes no green claim.
Does a green tariff mean renewable electricity reaches my home?
No, and no supplier can make that true. There is one grid and the electrons in your wires come from whatever was generating nearby at that moment. What a green tariff buys is a certificate — a Renewable Energy Guarantee of Origin — for each unit you use, retired on your behalf so nobody else can count it. That is an accounting claim about the national total, not a physical claim about your supply.
Is buying a green tariff pointless, then?
Not pointless, but weaker than the marketing suggests. Certificates can be bought separately from the electricity itself and cost a small fraction of a bill, so a supplier can source entirely from gas and still sell a "100% renewable" tariff. Tariffs backed by the supplier’s own generation, or by long-term contracts with specific wind and solar farms, do more than ones backed by bought-in certificates — and the difference is not visible in the label.
Why is there more coal in the residual mix than Britain burns?
Because of imports. Electricity arriving through the interconnectors is counted using the European Attribute Mix, which is far more coal-heavy than Britain’s own generation — and Britain’s own generation included no coal at all. That import share lands in the residual mix and lifts its coal figure well above anything actually burned here. DESNZ states the European figure in the notes to each release, and it moves: 38% coal in 2024, 32% in 2025.
Where do these numbers come from?
The Department for Energy Security and Net Zero publishes them once a year as the Fuel Mix Disclosure data table, under the Electricity (Fuel Mix Disclosure) Regulations 2005. It is the same table suppliers are required to use when they tell you what their own fuel mix was. It is published under the Open Government Licence.
