Elexon asked seven aggregators to prove the flexibility they sold

Between 29 October and 4 November, two markets spent the week on the same unglamorous question: how does anyone know how much flexibility was actually delivered, and who pays whom for it. In Britain the body that runs the electricity settlement code opened an assurance review into the independent aggregators trading flexibility in the wholesale market, and Ofgem told the industry what it wants those arrangements to deliver. In France, new rules on measuring demand response and on paying the supplier of an activated site came into force on 1 November.

Elexon asked seven independent aggregators how they calculate their volumes

On 29 October Elexon, which administers Great Britain's Balancing and Settlement Code, said it had asked independent aggregators active in the wholesale market to explain how they calculate the flexibility they provide. Those aggregators trade as Virtual Trading Parties, a role Elexon created in 2024 and whose activity has started to increase. Everything they sell rests on baselining: identifying which customer meters and assets are providing flexibility, working out how much electricity those assets would normally have used or generated had no flexibility action taken place, then comparing that estimate with what actually happened. A Virtual Trading Party may use Elexon's baselining methodology or its own, and when it uses its own the results arrive as Submitted Expected Volumes for each Settlement Period.

Elexon has now issued an Assurance Information Request to the seven Virtual Trading Parties that have been active in the wholesale market since April 2026. It is sampling their Submitted Expected Volumes and asking each company for evidence of how those volumes were calculated, to check the methods, controls and records behind them against the code's requirement to follow good industry practice, and to see whether approaches are consistent across the market. The findings go to the Performance Assurance Board in December 2026, which will decide whether anything further is needed; the conclusions will be published with individual parties removed, and Elexon plans to raise a BSC Issue so the industry can respond. Virtual Lead Parties, the independent aggregators that bid into the Balancing Mechanism, are already inside the 2026/27 BSC audit, and both roles join it from 2027/28.

Five days later the regulator set out its own frame. In an open letter published on 3 November, Ofgem said its long-term goal is that flexibility market arrangements deliver system and consumer value and help bring down bills for all consumers, and that while more participation and competition can support that goal, it should not come at the expense of it. The letter points at the live code modifications on compensation arrangements between suppliers and aggregators, among them P509, P510 and P502. Ofgem says it has contributed to the P509 and P510 workgroups, including presenting the challenges it sees with the existing P415 route, and that it has not yet formed a position on any of them. It will run further engagement with industry in late 2026, possibly into 2027, focused on baselining and on the compensation reference price, and will use that to decide whether regulatory intervention is needed.

Elexon described the same modifications on 4 November. P509 would give it a framework to assess, monitor and report the net benefits of demand-side response in the wholesale market, and is exploring a safety net for activity that does not deliver one. P510 would replace the mutualised compensation mechanism for independent aggregator activity with a direct, bidirectional mechanism. P511, approved by Ofgem in August and now implemented, drew eligibility boundaries for larger generation assets reaching the wholesale market through the P415 route. More than 100 individuals from more than 100 organisations have contributed across the four changes, and Elexon becomes a licensed Code Manager for the code in 2027.

If you aggregate C&I loads, batteries, chargers or PV in Britain, the method you use to state what you delivered is now something an assurance process will ask to see. Write down the baselining method you actually run, keep the inputs and the intermediate steps for every Settlement Period you submit, and be able to show why a volume is the number it is without rebuilding it by hand. If your route to market runs through somebody else's aggregation, put the same question to them before the Performance Assurance Board reads the findings in December. The compensation rules are still moving, so the safest position is one where your evidence survives whichever version of P509 and P510 lands.

Fusebox keeps that evidence inside the operating layer rather than beside it. Its interoperability module is built to connect outward instead of replacing what a customer already runs, with open APIs carrying telemetry, plans, results and reporting outputs between Fusebox and the forecasting tools, trading desk, controllers and partner systems on either side of it. That is the difference between knowing a volume and being able to hand someone else the trail behind it, which is what an assurance request asks for.

Talk to Fusebox about the data trail behind your volumes →

France changed what an aggregator pays the supplier, and how the reduction is measured

On 21 October the French regulator approved a new version of the general provisions of RTE's market rules, and the changes took effect on 1 November. The rules govern the versement fournisseur, the fixed amount a demand-response operator or balancing actor pays to the supplier of a site it has activated, to account for the electricity that supplier had planned to deliver. For telemetered sites in the regulated model, mostly tertiary consumers of small to medium size, the formula has been recut around the capacity mechanism that replaced the old one, whose delivery periods now straddle two calendar years. The scale moves from one annual update to two, covering 1 January to 30 September and then 1 October to 31 December. Profiled sites at or below 36 kVA keep a scale tied to the energy share of the regulated tariff, which already follows the new capacity price.

The same decision touches measurement. The panels method, introduced in September 2025, estimates what a profiled site would have consumed by comparing it with a sample of similar sites that are not modulating at that moment, and RTE may now extend the method's training window to periods after activation, which Enedis says will make the reference curve more reliable. The deadline for opening the method to sites connected to distribution networks other than Enedis moves from 1 July 2026 to 1 November 2027; the regulator accepted the delay, citing IT development that has run late at Enedis and the agence ORE, while asking both to finish sooner than the new backstop.

There is also a narrow derogation, and it shows how much the measurement matters. Each operator carries a reliability indicator, the ratio of the volumes it actually delivered to the volumes it was accepted for, taken over the second and third years before the one the indicator applies to. It is published under the operator's name on RTE's portal and it sets the maximum modulation that operator may value. Results from September to December 2025 will be taken out of the 2027 and 2028 indicators for entities that were using the panels method in those months, because the reference curves proved hard to anticipate while the method was new. Five of the six respondents wanted that extended into 2026 as well, and the regulator refused, saying four months was long enough to master the method or switch to another one. As Les Smart Grids reported, the practical task for aggregators, suppliers and network players is to check their compensation parameters, their measurement methods and their data exchanges against the new text.

For anyone selling demand response in France, two numbers moved in the same week: what the supplier is owed when your site is activated, and how much of your reduction is recognised in the first place. Price the compensation against the twice-yearly calendar before the October to December window is set, and look at how your measured volumes have tracked your accepted volumes over the past two years, because that ratio is public and it caps what you are allowed to sell. If you want to work through how the pieces fit before you talk to a person, the Fusie knowledge bot answers questions about the platform.

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What to watch

• Elexon takes its findings on Virtual Trading Party baselining to the Performance Assurance Board in December 2026, and plans to raise a BSC Issue on the back of it.
• Both independent aggregator roles enter the BSC audit from 2027/28, the year Elexon becomes a licensed Code Manager for the code.
• Ofgem's engagement on baselining and the compensation reference price runs through late 2026 and possibly into 2027, and decides whether it intervenes while P509 and P510 are still in the code process.
• In France the panels method must be open to profiled sites outside Enedis by 1 November 2027 at the latest, with the regulator pressing for an earlier date.
• The Nordic TSOs' accession to the European mFRR platform MARI, which their notice of 2 September now expects after next summer, with September or October 2027 the most likely window.