What are REGOs? The certificates behind every green tariff

When a supplier calls a tariff "100% renewable", the claim almost always rests on a certificate called a REGO. The certificate is real and the scheme is run by the regulator, but a REGO proves less than most people assume. This is how it works, where the claim is strong, and where it is mostly paperwork.

What a REGO is

REGO stands for Renewable Energy Guarantee of Origin. Ofgem issues one REGO to a renewable generator for each megawatt-hour (1,000 kWh) of electricity it produces, whether from wind, solar, hydro or eligible biomass. The certificate records that a unit of electricity was generated from a renewable source, and when. Generators receive REGOs from Ofgem at no cost; the certificates have value because suppliers need them to evidence a green tariff.

Why suppliers need them: the Fuel Mix Disclosure

Every licensed supplier has to publish an annual Fuel Mix Disclosure, the breakdown of where the electricity it supplied came from: renewables, natural gas, coal, nuclear and other. It is the pie chart you see on a bill or a supplier's website. To count a unit as renewable in that disclosure, and to label a tariff "100% renewable", the supplier retires one REGO per megawatt-hour it sells as green. The accounting runs over a compliance year from 1 April to 31 March. So REGOs are the unit of account behind the fuel mix; without retired certificates, a supplier cannot put a renewable figure on the page.

Bundled vs unbundled: the distinction that matters

Here is the hinge of the whole subject. A REGO can travel with the electricity it certifies, or it can be sold on its own, separately from the power.

• Bundled: the supplier buys renewable electricity and the certificates together, usually under a contract with a named generator. The certificate and the power come as a package.
• Unbundled: the supplier buys ordinary wholesale electricity, then buys loose REGO certificates from a broker to cover it. The certificate and the power have nothing to do with each other.

On paper the scheme treats both the same. A retired REGO is a retired REGO, and either way the tariff can carry a "100% renewable" badge. In substance they are worlds apart, because an unbundled certificate says nothing about where your electricity actually came from.

Why unbundled REGOs draw a greenwashing charge

The criticism comes down to price. Unbundled certificates are cheap and plentiful. One cost a supplier about 34p in December 2025, which works out at roughly £1 per domestic customer for a year of supply. For about a pound a household, a supplier can buy ordinary grid electricity all year, much of it generated by burning gas, then buy unbundled REGOs at the end and label the tariff "100% renewable".

The certificate does not change a single electron. On a still, dark evening the grid leans on gas whatever your tariff says, because electricity is physically pooled and you receive the same mix as your neighbour. So the label can be technically accurate under the rules and still tell a customer almost nothing about the impact of their money. That gap between the badge and the substance is what critics mean by greenwashing.

What stronger backing looks like

Not every green tariff is built this way. Three forms of backing carry more weight, roughly in order of credibility:

• Own generation. The supplier builds and runs its own wind, solar or hydro and supplies customers from it. The money you pay helps keep real renewable assets running.
• Power purchase agreements (PPAs). Long-term contracts to buy electricity directly from named renewable generators, with the REGOs bundled in. PPAs send money to specific projects and can underwrite the financing of new ones, which is the part that actually adds renewable capacity.
• Time-matched supply. Matching demand to renewable generation on a half-hourly or hourly basis instead of once a year, so the claim holds even at 6pm on a windless day. The methodology published by Matched Energy sets out how this is measured.

The reason time-matching matters: an annual REGO match can be satisfied even when your demand and the renewable generation never coincided. A windfarm's summer-night output can be used to certify your winter-evening usage. Half-hourly matching closes that timing gap, which is why it is the harder, more meaningful standard.

Where suppliers stand

Because the Fuel Mix Disclosure and the marketing labels look similar, 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 generators rather than relying on loose certificates. OVO has said it backs reform of the system and leans on power purchase agreements rather than unbundled REGOs. Other suppliers continue to back "100% renewable" tariffs largely with certificates bought on the open market. None of this is hidden, but none of it is on the front of the tariff either.

Is the system changing?

The distance between label and substance has drawn scrutiny from the regulator and the industry. Ofgem has examined how green tariffs are described and how transparent REGO backing is, with the direction of travel toward clearer labelling so that a tariff backed by unbundled certificates is not presented identically to one backed by generation or PPAs. The detail is still being worked through, so treat any "green" label as a prompt to ask how it is backed rather than a settled answer.

How to check your own tariff

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

• Is the tariff 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?

A green tariff that funds new generation does more for decarbonisation than one that retires leftover certificates, even when the two cost about the same.

How we use this in our rankings

This is why our Sustainability score reads the Ofgem Fuel Mix Disclosure rather than the marketing label, and carries a REGO asterisk: a high renewable percentage backed only by unbundled certificates is not treated as equal to one backed by generation or PPAs. Where a supplier has moved away from unbundled REGOs, such as OVO's shift toward power purchase agreements, we note it. You can see each supplier's disclosed fuel mix on its profile, for example Good Energy, Ecotricity, OVO and Octopus. For the shorter version of this argument, see how green is your green tariff?.