The short answer
A UK green energy tariff is a contractual claim backed by certificates, not a separate supply of electricity to your house. Your supplier matches the electricity you use with renewable generation by buying and retiring Renewable Energy Guarantees of Origin (REGO) certificates, and Ofgem's Standard Licence Condition 21D requires that claim to pass three tests: evidence of supply, additionality and transparency.
The UK grid was already 48.0% renewable in 2025/26 on the government's own fuel mix disclosure basis, so a green tariff does not change the mix in the wires. What it changes is the number your supplier reports, and — sometimes — whether your money funds new generation. Both of those statements are true at once, and any guide that gives you only one of them is selling you something.
If you own solar, the tariff decision that moves real money is the export rate and the time-of-use bands, not the green badge. Self-using one kilowatt-hour avoids the 26.32p Q4 2026 price cap rate. Exporting that same kilowatt-hour earns about 6p on our default SEG assumption. That is a 20.32p gap per kWh, and it is usually worth far more than the label on the tariff.
Most mass-market green tariffs sit at or below the price cap, because certificates are cheap relative to the electricity they label. A minority charge a genuine premium, and Ofgem lets them do it: suppliers that directly fund new renewable generation can hold a derogation from the default tariff cap. Knowing which of the two you are buying is the whole point of this guide.
What a green energy tariff actually is
A green energy tariff is an electricity tariff where the supplier has matched the electricity you use with renewable generation, and can evidence that matching to Ofgem. "Matched" is the operative word. Nothing is routed to your property, no one visits, and your meter reads exactly the same electricity as your neighbour's.
Here is the mechanism, in the order it happens.
- Ofgem issues certificates. For every megawatt-hour of eligible renewable electricity generated in Great Britain, Ofgem issues one REGO. Eligible sources include wind, solar PV, hydropower, biomass meeting sustainability criteria, tidal and wave, and the renewable fraction of energy from waste.
- Suppliers buy them. REGOs are traded on an open market, and they trade separately from the electricity itself. That separation is the single most important fact in this article.
- Suppliers retire them. A supplier selling 50 GWh on a green tariff buys 50,000 REGOs and retires them against that sales volume on Ofgem's register. The certificates cannot then be used again.
- They report the result. Fuel Mix Disclosure, supply licence condition 21, requires every licensed supplier to publish annually how much of its electricity came from each source.
Ofgem administers the REGO scheme for Great Britain under the Electricity (Guarantees of Origin of Electricity Produced from Renewable Energy Sources) Regulations 2003, as amended. Since 1 January 2021 the EU no longer recognises UK REGOs, and from the disclosure period beginning 1 April 2023 EU Guarantees of Origin are no longer recognised for GB Fuel Mix Disclosure either — so the certificates backing a British green tariff are British certificates.
You are not buying renewable electrons. You are buying the right to claim renewable electrons — and Ofgem is the body that decides whether the claim is allowed to stand.
What "100% renewable" does and does not change
All electricity in Great Britain enters one grid and mixes together, so a green tariff cannot deliver renewable electricity to your home and non-renewable electricity to someone else's. The government publishes exactly what the mix is. For the disclosure period 1 April 2025 to 31 March 2026, UK electricity was 48.0% renewable, 31.4% natural gas, 13.7% nuclear, 4.7% coal and 2.2% other.
There is a second figure in the same dataset that almost nobody discusses, and it is the interesting one. Under paragraph 10 of the Electricity (Fuel Mix Disclosure) Regulations, the government also publishes a residual fuel mix — the figure that applies to electricity whose generation attributes are not tracked. That mix is 10.8% renewable, 65.3% gas, 11.4% coal, 7.1% nuclear and 5.4% other.
That gap — 48.0% against 10.8% — is precisely what certificates buy. Laid out plainly, three different ways of accounting for the same 4,100 kWh of household electricity look like this:
| Basis | Intensity (g CO2/kWh) | Annual CO2 at 4,100 kWh |
|---|---|---|
| DESNZ national average (physical generation, 2025) | 147 | 603 kg |
| Residual fuel mix, for untracked supply | 396 | 1,622 kg |
| REGO-backed 100% renewable (market-based Scope 2) | 0 | 0 kg |
Residual figure calculated from the DESNZ per-source intensities in the same table (coal 921, gas 365, nuclear 0, renewables 0, other 969 g/kWh) weighted by residual shares; national average of 147 g/kWh is DESNZ's published figure. Consumption uses our standard 4,100 kWh household assumption, the same one behind the embeddable savings calculator.
Read those three rows together and the honest conclusion is uncomfortable but useful: a green tariff changes the number in the report far more than it changes the number in the sky. The 603 kg and the 1,622 kg are physical; the zero is an accounting position that the certificate market makes legitimate. That does not make green tariffs pointless — it tells you what you are actually buying, which is leverage over how suppliers buy power rather than a private wind farm.
Because REGO certificates trade separately from electricity, a supplier can buy its physical power from any source, hold enough certificates to cover its green-tariff customers, and lawfully describe that tariff as 100% renewable. Ofgem knows this. It is exactly why the licence condition below includes an additionality test rather than a certificates test.
How Ofgem regulates green tariff claims
Green electricity tariffs in Great Britain are regulated under Standard Licence Condition 21D of the Electricity Supply Licence, which imposes three requirements on any supplier claiming an environmental benefit: evidence of supply, additionality, and transparency. A supplier that cannot meet the additionality test must say so prominently, next to the claim.
| Test | What it requires |
|---|---|
| Evidence of supply | Enough REGO certificates to match the volume sold on the green tariff, with associated certificates retired so the same unit cannot be sold twice. |
| Additionality | The environmental benefit must happen because consumers chose the tariff, not solely because of subsidies, obligations or other mandatory mechanisms. |
| Transparency | Where there is no environmental benefit beyond what bills and taxes already fund, the supplier must say so clearly, prominently and close to the claim. |
Ofgem's phrasing on the transparency duty is unusually blunt for a regulator, and worth quoting directly. Suppliers must "clearly say if a tariff does not offer any environmental benefit other than those that consumers already pay for through costs embedded in their energy bill or through taxation".
On additionality, Ofgem's stated requirement is that suppliers "show that environmental benefits happen because consumers chose a tariff and not solely due to subsidies or supplier obligations".
The history matters here. Ofgem's Green Supply Guidelines were published in 2009 and implemented through a voluntary certification scheme — the Green Energy Supply Certification Scheme — with an independent panel and annual audits. Suppliers drifted away from it, and the certification label quietly stopped being a useful signal. Ofgem's response was to move the substance into the licence, which is why "certified green" badges are now rarer than the underlying rules. The rule you can rely on is SLC 21D, not a logo.
Why some green tariffs cost more than the price cap
The Ofgem price cap does not cap fixed deals, and it does not apply at all to tariffs that hold a derogation — permission to charge above the cap on the grounds that the money funds new renewable generation. Ofgem's price cap for 1 October to 31 December 2026 is 26.32p/kWh electricity and £1,723 for a typical dual-fuel household paying by Direct Debit, a rise of 4% on the July 2026 cap, confirmed on 26 August 2026.
Ofgem operates a formal derogation framework for renewable tariffs, last updated on 23 July 2026. The criteria a supplier must meet include customer choice, expectations on evidence, principles for assessing renewable support, and renewable costs and investments. A derogation is not a loophole — it is a judgement that a particular tariff does something the cap would otherwise punish.
Ecotricity is one of the suppliers holding one, and its own explanation on its tariffs page is the clearest statement of the trade-off you will find anywhere:
"Ofgem agreed that Ecotricity's Green Variable Tariff shouldn't be restricted by the price cap, because we're investing money from our customers' bills into new sources of renewable energy. We call this 'Bills into Mills'. We set our prices at a level that enables us to do what we're here to do — build new sources of green energy."
So there are two legitimate products on the market, and they are not the same thing:
| Type | What you are paying for | Typical price |
|---|---|---|
| Price-capped green tariff | Certificate matching on a standard tariff | At or around the cap: 26.32p/kWh (Q4 2026) |
| Derogated green tariff | Certificate matching plus direct investment in new generation | Set commercially; not capped |
Paying a premium for the second kind is a defensible choice. Paying a premium while believing you are on the first kind is not, and the transparency duty under SLC 21D is what stops a supplier from letting you make that mistake quietly. Use the three checks in the final section before you sign anything.
Which tariff should you be on?
Match the tariff structure to your hardware, not to its colour. A time-of-use tariff with a high peak export rate is worth several hundred pounds a year to a home with a battery, and almost nothing to a home without one. The rates below are London (GSP region C) figures pulled from Octopus Energy's own public tariff API on 14 September 2026.
| Your setup | Structure that pays | Verified 2026 rates |
|---|---|---|
| Solar only | Best flat export (SEG) rate | Open-to-all flat rates run from about 1p to 13p/kWh; 13p is the best truly open rate on our SEG tracker |
| Solar + battery | Time-of-use import and export | Octopus Flux — import 15.29p / 25.47p / 35.66p; export 5.24p / 9.80p / 28.60p peak |
| Solar + EV | Fixed cheap overnight window | Octopus Go — 8.63p between 00:30 and 05:30, 30.99p the rest of the day |
| Solar + heat pump | Heat-pump-friendly bands | Cosy — 13.07p off-peak, 26.63p standard, 39.95p peak; or OVO Heat Pump Plus at 15p |
The Flux numbers contain the whole argument. Its peak export rate of 28.60p is about 2.2 times the best open-to-all flat SEG rate of 13p, and its own import spread runs from 15.29p to 35.66p — a 2.33× range across three windows in a single day. Nothing in the green-tariff label comes close to that arithmetic. Structure beats colour.
Two caveats, both honest ones. First, time-of-use rates vary by distribution region and refresh regularly, so treat the table as a shape rather than a quote — confirm your postcode rate before switching. Second, and more important: tariff arbitrage and solar self-consumption compete for the same battery capacity. Every kilowatt-hour you cycle to the grid at 28.60p is a kilowatt-hour you cannot self-use at 26.32p, and every kilowatt-hour you self-use is one you cannot arbitrage. They are not additive. Our home battery ROI guide works through that constraint in full, including where it turns a battery's payback negative.
Model your region, system size and battery in the battery and Powerwall ROI calculator, or compare a battery build against a no-battery build side by side in the system comparison tool.
Green tariffs and heat pumps
With a heat pump, the tariff matters more than the green label, because a heat pump moves your heating from gas at roughly 7p/kWh to electricity at 26.32p/kWh on the Q4 2026 cap. Heat pump tariffs fix that gap by giving the heat pump its own cheaper rate, and the two best-known products are OVO Heat Pump Plus and Octopus Cosy.
OVO Heat Pump Plus charges an effective 15p/kWh for the electricity your heat pump uses, while the rest of your home stays on your normal tariff. It is a free add-on available on any OVO plan, and OVO puts the saving at around £350 a year against a standard variable tariff. The mechanics are worth understanding because they trip people up: you pay your normal unit rate for everything, and OVO credits the difference back in the first seven working days of the following month. If your standard rate is 28p, that credit is 13p for every kWh the heat pump consumed.
Eligibility is the constraint. You need a compatible connected heat pump — Vaillant aroTHERM or Viessmann Vitocal models are the named ones — plus a smart meter sending half-hourly readings, because OVO needs the heat pump's own consumption data to calculate the credit. Crucially for readers of this site, OVO states there are no restrictions on customers with solar or battery SEG.
Cosy takes the other approach: three cheap bands a day at 13.07p/kWh, a standard band at 26.63p and a peak at 39.95p, on the assumption that you can run the heat pump hard in the cheap windows and mostly leave it alone between 4pm and 7pm. Run Cosy badly — heating hard at 5pm — and the 39.95p peak punishes you harder than the cap ever would.
Either way, check the grant position before you buy hardware. The Boiler Upgrade Scheme offers a voucher of up to £7,500 in England and Wales, and Home Energy Scotland offers a grant of up to £7,500 with a loan option. Our solar and heat pump guide covers the combination in detail, and the grants guide covers every scheme currently open.
Rewards: what you can actually earn on top
Rewards are where a green tariff can outperform a cheaper one, because they pay you for shifting usage rather than for the colour of your supply. Octopus's Octoplus programme is the largest retail example and publishes its own numbers: the company says each Octoplus customer had access to over £300 of rewards last year, equivalent to roughly 17% of annual energy costs on a typical bill, and that it gave away £19 million in rewards across the year. By the end of August 2026 it had already given away £11 million.
How Octoplus works, from Octopus's own page:
- Eligibility: electricity supplied by Octopus, a smart meter sending half-hourly readings, and payment by Direct Debit. You can be on any standard or smart Octopus tariff — no specific tariff required.
- Octopoints: the currency is Octopoints, converting at 800 points = £1, usable as bill credit, at double value on Octopus's merchandise shop, or donated to charity.
- Power Down and Power Up: earn points for using less electricity when the grid is strained, or more when it is "overflowing with green electrons". Octopus states it needs 80% of your half-hourly readings over the last 20 days to measure the baseline.
- Weekend Happy Hours: Power Down on two weekdays and you get an hour of free electricity at the weekend. Octopus's page notes this runs until 1 November.
- Referrals: split £100 with the person you refer, plus 800 Octopoints for you and 500 for them.
The historical payouts give a sense of scale: Octopus reports £1,723,940 earned in free electricity sessions between 1 January 2024 and 1 September 2025, and £1,034,504 worth of Octopoints in Saving Sessions between 1 November 2023 and 1 September 2025.
Behind the retail programmes sits the national scheme. The Demand Flexibility Service, run by Neso (the National Energy System Operator), launched in winter 2022/23 and became a year-round service on 27 November 2024. It was expanded on 9 April 2026 to add bi-directional flexibility, zonal procurement and a Self-Nominated Baseline option, and to cut the eligibility threshold to 0.1MW. From 7 October 2026 it will also procure constraint management actions, absorbing the Local Constraint Market.
One honest caveat on DFS: Neso pays the provider, and for households the provider is a registered supplier or aggregator, not you directly. Neso publishes lists of registered providers split between domestic households and everyone else. The headline pence-per-kWh figures you see advertised are retail offers built on top of that wholesale arrangement, so compare them like any other tariff rather than treating them as a regulated rate.
How to check a green tariff in three steps
Three checks settle whether a green tariff is worth its price: the supplier's published fuel mix, whether it buys generation or only certificates, and whether it holds a price-cap derogation. None of them requires technical knowledge, and all three are published.
- Read the Fuel Mix Disclosure. Supply licence condition 21 requires every licensed supplier to publish it annually. Compare the renewable percentage with the 10.8% residual mix in the government's data table. A supplier claiming 100% renewable across the board while disclosing a low renewable share in its actual fuel mix is telling you it relies on certificates rather than purchase.
- Ask whether they buy generation or certificates. A supplier that owns assets or holds long-term power purchase agreements with named UK generators is doing something structurally different from one buying REGOs on the open market. The transparency duty under SLC 21D obliges them to be clear about which one applies to your tariff, and vague answers buried in small print are the signal you are looking for.
- Check for a price-cap derogation. Ofgem publishes the derogation guidance and criteria. A derogation is the strongest published evidence that a tariff funds something beyond certificates, because it is the one mechanism that lets a supplier charge above the cap — and Ofgem only grants it against evidence of renewable investment.
Compare import cost minus export income on the same day for each option, not the import rate alone. And read our guide to switching energy provider with solar panels first — your SEG payments do not follow your supply switch automatically, and that is the mistake that costs solar owners the most money.
See what a tariff change is actually worth to you
Put your usage, region and system size in and compare the annual figures side by side.
Open the savings calculatorFAQs
What is a green energy tariff?
A green energy tariff is an electricity tariff where the supplier has matched the electricity you use with renewable generation and can prove it to Ofgem. The matching is done with Renewable Energy Guarantees of Origin certificates. It is a contractual claim recorded in the supplier's accounts, not a separate supply of electricity to your home: all electricity in Great Britain flows through one grid and mixes together.
Does a green tariff change the electricity that reaches my home?
No. Every unit of electricity in Great Britain goes into the same grid, so a green tariff cannot separate renewable electrons from the rest. In 2025/26, 48.0% of UK electricity was already renewable according to the government's fuel mix disclosure data, so the mix at your meter is roughly half renewable whether or not you pay for a green tariff. What a green tariff changes is the certificates your supplier retires on your behalf.
What is a REGO certificate?
A REGO (Renewable Energy Guarantee of Origin) is a certificate issued by Ofgem for every megawatt-hour of eligible renewable electricity generated in Great Britain. Suppliers buy REGOs and retire them against the volume they sell on a green tariff, then report the result through Fuel Mix Disclosure. REGOs trade separately from the electricity itself, so a supplier can hold certificates while buying its physical power from any source.
Are green energy tariffs more expensive?
Not necessarily. Most mass-market green tariffs are standard price-capped deals with REGO backing, so they cost the same as the equivalent non-green tariff. A minority charge a genuine premium: Ofgem's derogation framework lets a supplier be exempt from the default tariff cap if it directly funds new renewable generation, and Ecotricity's Green Variable tariff is one example. The honest test is whether you are paying above the 26.32p/kWh Q4 2026 cap for a certificate or for new generation.
Can I get a green tariff if I have solar panels?
Yes, and having solar does not restrict which tariffs are available to you. Your panels, inverter, MCS certificate and DNO notification are unaffected by which company supplies your import electricity. If you are on a green tariff you can still claim the Smart Export Guarantee for your exports, because SEG is a separate contract that does not have to be with your import supplier.
Do I keep my SEG payments if I switch to a green tariff?
Only if you arrange it. SEG tariffs are not transferred automatically between suppliers. Ofgem's rule is that you can hold a SEG tariff with any SEG licensee and that your SEG licensee does not need to be the same company as your electricity supplier, so you can switch supply and keep exporting to your existing payer. Many of the highest-paying SEG rates are conditional on being a supply customer, so check whether the rate you want moves with you.
What is the best tariff for solar panels and a battery?
A time-of-use import and export tariff. Using Octopus's own tariff API for London on 14 September 2026, Octopus Flux charges 15.29p off-peak, 25.47p in the day and 35.66p at peak, and pays 5.24p, 9.80p and 28.60p for export in those same windows. That 28.60p peak export rate is about 2.2 times the best open-to-all flat SEG rate of 13p, which is where most of a battery's extra income comes from.
Is there a special tariff for heat pumps?
Yes. OVO's Heat Pump Plus charges 15p/kWh for the electricity your heat pump uses, on top of any OVO plan, if you have a compatible connected heat pump and a smart meter sending half-hourly readings; OVO puts the saving at around £350 a year. Octopus's Cosy tariff is the other main option, with off-peak bands at 13.07p against a 39.95p peak. Neither is restricted to homes without solar.
Can I get paid for using less electricity at peak times?
Yes, through the Demand Flexibility Service run by Neso, the National Energy System Operator. It launched in winter 2022/23, became a year-round service on 27 November 2024, and was expanded on 9 April 2026 with bi-directional flexibility and a lower eligibility threshold of 0.1MW. Households take part through a registered provider, which is usually an energy supplier or an aggregator, and Neso publishes the list of registered domestic providers.
What are Octopus Octoplus rewards worth?
Octopus states that last year each Octoplus customer had access to over £300 worth of rewards, equivalent to roughly 17% of annual energy costs on a typical bill, and that it gave out £19 million in rewards across the year. In 2026 it had already given away £11 million by the end of August. Octopoints convert at 800 points to £1. To join you need Octopus electricity supply, a smart meter sending half-hourly readings, and Direct Debit.
What is the residual fuel mix?
The residual fuel mix is the figure the government publishes under paragraph 10 of the Electricity (Fuel Mix Disclosure) Regulations for electricity whose generation attributes are not tracked. For 2025/26 it is 65.3% natural gas, 11.4% coal, 7.1% nuclear, 10.8% renewables and 5.4% other fuels. It matters because it is more fossil-heavy than the grid as a whole, which was 48.0% renewable on the same disclosure basis.
How do I check whether a green tariff is genuine?
Three checks. First, read the supplier's Fuel Mix Disclosure, which every licensed supplier must publish annually, and compare its renewable percentage with the 10.8% residual mix. Second, ask whether the supplier buys renewable generation through its own assets or power purchase agreements, or only buys certificates separately. Third, check whether the supplier holds a derogation from the Ofgem price cap, which Ofgem grants only where a tariff directly supports renewable investment.
Sources
- Ofgem — Standard Licence Condition 21D, Electricity Supply Licence (green and renewable tariff requirements: evidence of supply, additionality, transparency)
- Ofgem — Final proposal on improving domestic consumer protection in the green and renewable energy tariffs market, and accompanying press release
- Ofgem — Default tariff cap derogations for renewable tariffs, guidance last updated 23 July 2026
- Ofgem — REGO Guidance for generators, agents and suppliers, v4.0, March 2026; guidance on Guarantees of Origin and Fuel Mix Disclosure
- Ofgem — October 2026 price cap announcement, 26 August 2026 (26.32p/kWh electricity, £1,723 typical dual-fuel bill, +4%)
- GOV.UK / Department for Energy Security and Net Zero — Fuel mix disclosure data table, 2025 to 2026, published 3 August 2026 (residual fuel mix, UK fuel mix, emissions intensities, loss factor 1.1098)
- Octopus Energy — public tariff API (api.octopus.energy), London GSP region C unit rates for Flux, Cosy, Go and Outgoing, read 14 September 2026
- Octopus Energy — Octoplus rewards programme page (octopus.energy, read 14 September 2026)
- Neso (National Energy System Operator) — Demand Flexibility Service (neso.energy, read 14 September 2026)
- OVO Energy — Heat Pump Plus eligibility, rate and credit mechanics (ovoenergy.com, read 14 September 2026)
- Ecotricity — green tariffs and price cap derogation explanation, "Bills into Mills" (ecotricity.co.uk, read 14 September 2026)
- EDF Energy — How green is your energy tariff? (edfenergy.com, read 14 September 2026)
Sources listed above are the primary documents behind every figure in this guide. Tariff rates change, usually with around 30 days' notice, and vary by distribution region — always confirm the live rate with the supplier before switching.
Disclaimer: this guide is for general information only and is not financial, legal or energy-contract advice. uksolarcalc.co.uk is not an energy supplier, a broker or a price comparison service, and we do not receive commission from the tariffs described. Boiler Upgrade Scheme and Home Energy Scotland figures are quoted from the administering bodies and depend on your property and installer. Always confirm eligibility, rates and terms directly with the supplier or scheme administrator.