The 'Green' Tariff Greenwash: How to Audit Your Supplier's Claims

Most British households on "green" tariffs pay £45-90 extra annually for Renewable Energy Guarantee of Origin (REGO) certificates that match consumption to existing generation, not new build. The grid's physical electrons remain unchanged; only the accounting shifts. Audit claims by checking supplier fuel mix disclosures against Ofgem's residual mix data and questioning additionality—whether your money funds new capacity or merely retitles old output.

The REGO Mechanism: Accounting, Not Infrastructure

REGO certificates cost roughly £1-2 per megawatt-hour on wholesale markets. A typical household consuming 3,100 kWh/year needs 3.1 certificates. Suppliers bundle these cheap administrative instruments with brown power, match them to your usage, and market the result as "100% renewable." The underlying electricity comes from the same grid mix as your neighbour's standard variable tariff. This isn't fraud—it's how the system was designed—but it means your green premium rarely builds turbines.

Additionality: The Test Most Tariffs Fail

Genuine green tariffs demonstrate additionality: your spending directly causes new renewable capacity that wouldn't exist otherwise. Ecotricity and Good Energy historically scored well here, owning generation assets and building new sites. Most large suppliers—including those with heavily marketed green products—buy REGOs on the open market without contractual links to construction. Check supplier annual reports for capital expenditure on new renewables versus marketing spend on "green" branding. The ratio rarely flatters.

How to Read Your Supplier's Fuel Mix Disclosure

Ofgem requires annual fuel mix disclosure by 1 October for the previous calendar year. Find yours in your online account or request it directly. The table shows percentages by source: wind, solar, biomass, nuclear, natural gas, coal. Compare this to the UK residual mix—the average generation excluding surrendered REGOs—published by the Association of Issuing Bodies. If your supplier claims 100% renewable but the residual mix shows 38% fossil fuel, you're buying certificates, not physical green power.

*Octopus matches REGOs at no premium; **invests in new capacity through separate arms

Residual Mix: The Hidden Benchmark

The UK residual mix for 2024—published July 2025—was 38.2% natural gas, 14.7% nuclear, 13.1% wind, 6.8% solar, 11.4% biomass, 15.8% unspecified imports. Any supplier claiming 100% renewable without own-generation is mathematically impossible against this baseline unless using REGO retirement. The residual mix represents what actually flows through cables after certificates are stripped away. Your green tariff doesn't change this figure; it only changes whose name sits on the paperwork.

The Time-of-Use Complication

Green claims become murkier with time-of-use tariffs. If you're on a time-of-use tariff charging different rates by half-hour, your actual consumption may occur when grid carbon intensity peaks—typically 17:00-20:00 when solar output collapses and gas turbines ramp. Some suppliers now offer "green" time-of-use products claiming to match consumption to real-time renewable generation. Check whether they use actual half-hourly matching or annual REGO averaging. The latter misses the point entirely.

Biomass and the "Renewable" Loophole

Biomass qualifies as renewable under UK rules but carries disputed carbon credentials. Drax Power Station—source for several green tariffs—burns imported wood pellets with lifecycle emissions contested by scientists. Your supplier's fuel mix disclosure lumps biomass with wind and solar under "renewable" percentages. Request the breakdown: some tariffs are 30-40% biomass by REGO volume. If your priority is emissions reduction, this matters. If it's renewable credentials on paper, it doesn't.

What Your Money Actually Buys

Trace the cash flow. On a £52 annual premium, approximately £3-6 covers REGO certificates. The remainder funds marketing, margin, and occasionally community funds with loose additionality tests. Some suppliers divert portions to carbon offset schemes—tree planting with 20-40 year sequestration horizons while your electricity burns fossil fuels today. Others, like those offering device-level optimisation, at least reduce your absolute consumption. The green tariff itself rarely does.

Auditing Your Own Supplier: A Checklist

Request their latest fuel mix disclosure and REGO retirement records. Ask specifically: "What new renewable capacity did customer premiums fund in 2024-25?" Check Companies House filings for related-party generation asset ownership. Compare their claimed renewable percentage against the residual mix—excess above residual indicates certificate purchasing, not physical supply. Finally, calculate your premium per tonne CO2 "avoided" using their methodology. Figures above £200/tonne suggest you're subsidising marketing, not mitigation.