British households paying for ‘100% renewable’ electricity are being systematically misled. New analysis of supplier data reveals that some power marketed as fully renewable, generated in the UK primarily by wind and solar power, actually contains as little as 56% renewable electricity. The remainder comes from gas-fired and nuclear generation.

This isn't fraud. These suppliers are following the rules perfectly. The problem is the rules themselves: a 20-year-old accounting system that allows renewable claims to be reconciled annually rather than when power is actually generated and consumed.

When Renewable Energy Guarantees of Origin (REGOs) launched in 2003, renewables generated less than 3% of our electricity. Annual reconciliation seemed reasonable then. Today, with renewable sources varying from 5% to 80% of generation depending on weather and season, this temporal disconnect has become a chasm that undermines both consumer trust and our clean power ambitions.

The issue isn't REGOs themselves – certificates that track renewable generation are valuable. But, unlike every other part of our electricity system, which must balance supply and demand in real time, REGOs need only match annual consumption. That allows suppliers to maintain their ‘100% renewable’ claim by accumulating certificates during summer when solar is cheap and plentiful, then sell fossil-fuelled electricity on windless winter evenings. I know from building grid-scale storage at Tesla that matching supply with demand is the fundamental challenge of any electricity grid. With renewables now exceeding 50% of the UK’s generation, this challenge has intensified. Yet our accounting system pretends this temporal matching doesn't matter.

The data now proves otherwise. Reforms at Elexon have made half-hourly market data publicly available for the first time. Combined with Ofgem's REGO database and generation data from the National Energy System Operator, we can track, every 30 minutes, what suppliers actually deliver versus what they claim. We have spent months working closely with leading suppliers to develop our methodology, which has been reviewed by industry experts at organisations including the University of Oxford, Imperial College, Good Energy and npower. 

What were the results?

The results reveal a spectrum of quality. The top three suppliers provide energy which exceeds 75% renewables content when measured properly, procuring renewable power aligned with customer demand. These suppliers are genuinely investing in the infrastructure and contracts needed to deliver clean power when their customers need it. They deserve recognition for this commitment.

But they compete against rivals making identical marketing claims through annual certificate accumulation. The supplier delivering only 56% renewable power can legally claim to be ‘100% renewable’ – not through meaningful investment in renewables, but by operating within an outdated reporting framework.  

The consequences extend beyond consumer trust. The UK government’s Clean Power 2030 plan requires massive investment in not just generation but also storage and grid flexibility. Why would suppliers invest in securing renewable power during difficult periods – precisely when the grid needs it most – when they can make identical claims by stockpiling cheap summer certificates?

The world is already moving past current regulations. Google and Microsoft ask for half-hourly matching from suppliers. Australia launches time-stamped certificates next year. Ireland and Denmark have proven the technology through successful pilots. Even the GHG Protocol that underpins global carbon accounting is shifting toward temporal matching. Yet Britain, which pioneered electricity market reform, clings to annual reconciliation.

The technical solution is straightforward. REGOs should record the half-hour in which electricity is generated. Suppliers should match these time-stamped certificates with customer demand in real time. There is nothing new here; the data systems already exist. Several suppliers already do this voluntarily.

Why would suppliers invest in securing renewable power during difficult periods – precisely when the grid needs it most – when they can make identical claims by stockpiling cheap summer certificates? 

The last government acknowledged REGO reform is necessary, and current ministers have also been clear they want to put more power in the hands of consumers to give them greater control and choice. With the technical infrastructure ready and international momentum building, what's needed now is political will to update rules written when renewable energy was an aspiration rather than the majority of our power.

In October, Matched – the independent not-for-profit initiative I founded to bring transparency to renewable claims – will publish the Matched Clean Power Index. Using publicly available data, we will rate every major supplier on their true renewable percentage. Consumers deserve this transparency. Suppliers investing in genuine renewable procurement deserve recognition. And Britain's climate commitments deserve an accounting system that reflects physical reality.

For the first time in 20 years, we have the data to align renewable energy claims with power that actually flows through the grid. We can restore trust in clean tariffs. We can create proper incentives for the investments that Clean Power 2030 requires. REGOs clearly need to be updated; the question is whether we have the courage to admit the current system has outlived its purpose.

The views and opinions expressed in this article are strictly those of the author only and are not necessarily given or endorsed by or on behalf of the Energy Institute. 

• Further reading: 'Next steps announced in development of UK electricity flexibility markets'. Elexon has published a plan for the handover of UK flexibility market rule development from the Energy Networks Association’s (ENA) Open Networks (ON) programme, which closes in July 2025.