How green is your green tariff? REGOs vs matched supply

Most UK suppliers sell a "100% renewable" electricity tariff. The label can mean two very different things, and the gap between them is the whole story. It comes down to how the renewable claim is backed. For the full scheme mechanics, see what are REGOs?; this piece is about what the label is worth to you.

The certificate behind the label

A "100% renewable" claim is almost always backed by REGOs, certificates Ofgem issues to renewable generators, one for every megawatt-hour they produce. Suppliers retire these certificates to evidence the renewable share on your bill. The catch is that a REGO can be sold separately from the electricity it certifies. These "unbundled" certificates are cheap and plentiful: one cost a supplier about 34p in December 2025, which works out at roughly £1 per customer for a year of supply. For about a pound a household, a supplier can buy ordinary wholesale electricity all year, much of it generated by burning gas, then buy unbundled REGOs at the end and label the tariff "100% renewable". Under the rules that label is accurate. In substance it can tell you almost nothing.

Why a green label can still mean grey power

Electricity is physically pooled. The power in your sockets is the same mix flowing to the rest of your street whatever tariff you are on, so a green label does not change a single electron. The grid leans on gas whenever wind and solar fall short, and an annual certificate match does nothing about that hour by hour. A wind farm's output on a breezy summer night can be used to certify your usage on a still winter evening, even though the generation and your demand never coincided. That gap, between a once-a-year paper match and what actually flowed down the wire, is the heart of the criticism.

What stronger backing looks like

A more credible green tariff is backed by one of:

• The supplier's own generation, where it builds and runs wind or solar and supplies customers from it.
• Power purchase agreements (PPAs), long-term contracts that buy power directly from named generators, with the REGOs bundled in.
• Time-matched supply, where demand is matched to renewable generation on a half-hourly basis rather than once a year, so the claim holds even at 6pm on a windless day. The Matched Energy methodology sets out how this is measured.

The reason time-matching matters is exactly the timing gap above: only a half-hourly match can say your demand lined up with real renewable output, rather than being squared off against a certificate at the end of the year.

The real test: does your money add new renewables?

The question that separates a meaningful green tariff from a cosmetic one is additionality: does your money help build or run renewable generation that would not otherwise exist? Retiring an unbundled certificate that a wind farm was always going to earn adds nothing. The wind farm runs either way and collects a few pence for the paperwork. A PPA that underwrites a generator's revenue, or a supplier building its own wind and solar, can tip new projects into being financed. Two tariffs can both say "100% renewable" while one funds new capacity and the other just reshuffles certificates that already existed. The prices are often similar, so the difference is in where the money goes, not what you pay.

How suppliers differ

Because the Fuel Mix Disclosure and the marketing labels look alike, the only way to tell tariffs apart is to read how each supplier sources its power. Good Energy and Ecotricity have long pointed to their own generation and direct contracts with named generators rather than loose certificates. OVO has said it backs reform and leans on power purchase agreements rather than unbundled REGOs. Several large suppliers continue to back "100% renewable" tariffs mostly with certificates bought on the open market. None of this is hidden, but none of it is on the front of the tariff either, which is why the badge alone tells you little.

What to check before you switch

Four questions separate a strong green tariff from a paper one:

• Is it backed by the supplier's own generation, by PPAs, or by unbundled REGOs?
• Does the supplier report any time-matching, or only an annual match?
• Does buying it help fund new renewable generation, or just retire existing certificates?
• What does the supplier's Fuel Mix Disclosure actually show, beyond the tariff's headline label?

How we treat it in our rankings

Our Sustainability score reads the Ofgem Fuel Mix Disclosure and carries a REGO asterisk rather than taking a "100% renewable" label at face value, and it notes where a supplier has moved away from unbundled certificates. The full breakdown is in what are REGOs?, and you can see each supplier's disclosed fuel mix on its profile, for example Good Energy, Ecotricity and OVO.