The short answer
£1,641
Ofgem price cap
Typical dual-fuel direct-debit, 1 April to 30 June 2026 (Ofgem)
24.67p
Electricity unit rate
Cap rate per kWh, April to June 2026
1 MWh
1 REGO certificate
The unit suppliers buy to label a tariff ‘100% renewable’
~£1
REGO market price
Approximate cost to make 1 MWh of normal power look ‘green’
A truly green supplier sources renewable electricity directly, usually through a power-purchase deal with a wind, solar or hydro generator. A "badged" green supplier buys cheap REGO certificates to match the volume you use. Both can legally call their tariff 100% renewable. The difference matters.
The belief most UK customers hold (and why it costs them)
Most UK households assume that picking a "100% renewable" tariff means the electricity flowing into their plug is generated by wind turbines or solar panels. It feels intuitive. You pay a green supplier, so green electrons must be flowing your way.
That is not how the grid works. Once electricity enters the national grid, it mixes. Every home in Great Britain pulls from the same pool. Your plug does not know if the power came from a turbine in the North Sea or a gas plant in Pembrokeshire.
What suppliers can do is buy or earn a piece of paper, called a REGO certificate (Renewable Energy Guarantees of Origin), for every megawatt-hour (1,000 kWh) of green power generated in the UK. The supplier matches the certificates to your usage at the end of the year. Mission accomplished, on paper.
In 2026 the government is consulting on tightening these rules precisely because a tariff can be sold as 100% green when the supplier has done little more than buy certificates from a wind farm that would have produced the same electricity anyway.
Why most "best green supplier" guides get it wrong
Type "best green energy supplier UK" into any search engine and you get the same list: a handful of recognisable names, a paragraph each, and a verdict based on price. That brief is missing the only thing that actually decides whether a tariff is green.
A useful comparison must answer three questions:
- Does the supplier generate its own electricity? Owning wind, solar or hydro assets means real new green capacity, not certificate trading.
- Are there long-term contracts with generators (PPAs)? A power-purchase agreement gives a wind farm guaranteed income. That is what gets new turbines built.
- What is the gas side made of? Most "100% green" tariffs cover only electricity. Gas is almost always natural gas with a small green-gas blend or carbon offsets bolted on.
Skip those three questions and a comparison is just a price chart with leaves on it.
How UK green tariffs actually work
What a REGO certificate really is
A REGO is a digital document issued by Ofgem to anyone who generates 1 MWh (1,000 kWh, about three months of average household electricity) from renewable sources in the UK. Suppliers must use REGOs each year to back up any "green" claim on a tariff.
The catch: REGOs are traded separately from the electricity itself. A wind farm can sell its electricity to one company on the wholesale market, then sell its REGO certificates to a different supplier for around £1 per MWh. That second supplier can now label a tariff "100% renewable" without buying a single green electron.
The three ways a supplier can label a tariff "green"
Own generation
The supplier runs its own wind farms, solar parks or hydro plants. Real new capacity, the strongest form of green.
Power-purchase deals
A long-term contract with a named generator. Bundled REGOs and electricity. Solid, supports the renewable build-out.
REGO certificates only
The supplier buys cheap unbundled REGOs at the end of the year to match your usage. The electricity itself can come from anywhere on the grid.
All three are legal in the UK. Only the first two add anything real to the grid. The third can be done by any supplier of any electricity for under £30 a year for an average household. That is why you see so many "100% renewable" badges.
Green tariff truth checker
Tell the calculator below how much electricity you use, what your supplier claims, and how the supplier sources its power. It will rate how genuinely green the tariff is and compare your bill against the current Ofgem price cap.
Is your “green” tariff actually green?
Scored against the live Ofgem price cap
Your verdict
Ofgem default tariff cap, 1 Apr–30 Jun 2026: 24.67p/kWh unit rate, 57.21p/day standing charge. Electricity only.
Real-world impact on UK households
In practice, the certificate market lets normal grid power look identical to true green power on a bill. A UK household paying a small premium for a "100% renewable" tariff often pays an extra £20 to £80 a year for what is, at root, a paper match. The wind farm that produced the certificate would have built and run anyway.
Meanwhile, suppliers that actually own generation assets sometimes price below the Ofgem cap, because owning a wind farm hedges them against wholesale gas spikes. So the assumption that genuine green costs more is often backwards.
The trap that hits hardest is the green prepayment tariff. Customers on prepayment meters already pay more per kWh on average. A green badge on a prepayment plan rarely changes the underlying mix and rarely changes the price. If you can move from prepayment to direct debit on a credit meter, that single change usually saves more than any green choice.
Insider insight: the REGO loophole that is closing
Here is something the marketing pages do not say. As of May 2026 the UK government is consulting on tightening green-tariff rules through DESNZ (the Department for Energy Security and Net Zero) and Ofgem, after Citizens Advice and consumer groups complained that the REGO system was being used to mislead households.
The likely change is a requirement that suppliers disclose the type of renewable (wind, solar, hydro, biomass), when it was generated, and where the certificates were bought. Suppliers that already match their tariffs to specific wind or solar contracts will look better. Suppliers that quietly buy bulk REGOs in a single annual sweep will not.
If you can pick a supplier today that already publishes this detail, you are future-proofed against the rule change. Look for supplier "fuel mix" pages that name the wind farm or solar park behind your tariff, not just a percentage.
Green tariffs: where they help, where they do not
Advantages
- A genuine PPA or own-generation tariff supports new UK renewable capacity.
- Many genuinely green tariffs sit at or below the Ofgem price cap.
- Smart-meter green tariffs can pair with time-of-use rates and EV charging.
- Choosing carefully signals demand to investors building new UK wind and solar.
Disadvantages
- A REGO-only tariff puts no new green electrons on the grid.
- Green gas is barely available. Almost all dual-fuel 'green' tariffs use natural gas plus offsets.
- Prepayment customers see little benefit from switching to a green badge.
- Some green tariffs use exit fees that trap you when wholesale prices fall.
What UK customers should actually do, in order
- 1 Find out how your current supplier sources its renewables. Open the supplier's fuel-mix page. If it names PPAs and specific generators, that is a strong sign. If it only says "100% renewable" with no detail, treat it as a REGO-only label.
- 2 Compare on price and source. Use the calculator above as a sanity check before signing up. If the genuine-green score is under 50 and the price is above the cap, walk away.
- 3 Get a smart meter. It unlocks time-of-use green tariffs (cheap overnight wind, free Sunday-afternoon solar windows). Free from your supplier, no install cost.
- 4 Treat green gas separately. Only one UK supplier currently offers 100% green gas. Everywhere else, "green" gas means a tiny biomethane blend plus carbon offsets. Read the gas line on the tariff sheet, not the homepage.
- 5 Re-check every 12 months. The fuel mix, REGO rules and price cap all move. A 2024 "best green tariff" is not automatically the right one in 2026.
UK supplier fuel mix: what each supplier actually delivers
The table below shows the published electricity fuel mix for major UK suppliers. A 100% figure in the "Renewable" column is meaningful only if backed by PPAs or own generation. Use the type column to read this honestly.
| Supplier | Renewable % | CO2 g/kWh | Type of green |
|---|---|---|---|
| Ecotricity | 100% | 0 | Own wind |
| Good Energy | 100% | 0 | PPAs |
| Octopus Energy | 100% | 0 | PPAs + REGOs |
| E.ON Next | 100% | 0 | Mostly REGOs |
| OVO Energy | 100% | 0 | REGOs |
| EDF Energy | 29% | 42 | Nuclear-heavy |
| British Gas | 75% | 0 | Mixed |
| Scottish Power | 40% | 244 | Mixed |
| UK Average | 40% | 194 | Reference |
Sources: published supplier fuel-mix declarations, Ofgem Renewable Electricity Register (2025-26 data). "Type of green" is editorial classification based on whether the supplier owns generation, holds PPAs, or relies on unbundled REGOs.
Why this matters in 2026
The UK is rebuilding its electricity system around offshore wind, solar and storage. New green capacity needs steady, predictable income. That income comes from long-term contracts written by suppliers that are willing to commit. Every household on a PPA-backed tariff is, in effect, voting for a turbine to be built; small-scale options like energy harvesting on your own roof can add to that. Every household on a REGO-only badge is voting for the status quo with a coat of paint.
Look past the leaf logo. Check the fuel mix. Run the numbers against the price cap. That is what "best green energy supplier" actually means in 2026.
Frequently asked questions
From 1 April to 30 June 2026, the price cap is set at £1,641 a year for a typical dual-fuel household paying by direct debit. Electricity is capped at 24.67p per kWh with a daily standing charge of 57.21p. Gas is capped at 5.74p per kWh with a daily standing charge of 29.09p. The cap is reviewed every three months by Ofgem.
Not literally. The electrons you receive come from the same national grid as everyone else. What a 100% renewable tariff guarantees is that the supplier holds enough REGO certificates to cover the volume of electricity you use during the year. The depth of greenness depends on whether those certificates come bundled with real long-term contracts with renewable generators or are bought separately as cheap paper.
Often no. Suppliers that own renewable generation are partly hedged against gas-price volatility, so several PPA-backed tariffs sit at or below the Ofgem price cap. The assumption that green tariffs always cost more mostly held a decade ago. In 2026, price and source are independent and need to be checked together.
True 100% biomethane gas is rare. Only Green Energy UK currently offers a fully biomethane tariff at scale. Most green gas tariffs are mostly natural gas with a small biomethane percentage and carbon offsets covering the rest. The Green Gas Support Scheme is funding new biomethane plants, but the share of green gas in the grid is still in single digits.
Not entirely, but the choice is narrower and the price premium is usually higher. The single biggest win for a prepayment household is often switching to a credit meter on direct debit. Once on direct debit, the full range of PPA-backed green tariffs becomes available.
Re-check every 12 months, or whenever your fixed-term deal is within 49 days of ending. Ofgem allows you to switch in this window without paying exit fees. Check both the unit rate and the source of the renewable claim each time.