Most of the conversation about grid flexibility focuses on demand reduction — switching things off when the grid is under stress, usually on cold winter evenings when everyone’s cooking and the wind has dropped. But there’s a mirror problem that’s becoming increasingly common: too much electricity, generated by wind and solar at times when demand is low, that the grid has nowhere to put. The solution to that problem is demand turn-up, and National Grid ESO is running its most ambitious trial of it this coming winter.
The trial introduces a significant change: the removal of the Flexibility Compliance Limit for enrolled participants. Previously, aggregators and smart device platforms participating in the Demand Flexibility Service (DFS) faced a cap on how many enrolled devices could respond to a single flexibility event. The FCL was designed as a cautious measure during early trials — a circuit-breaker to prevent a synchronised surge in demand from thousands of devices all switching on simultaneously from creating instability elsewhere in the system. For winter 2026, that limit is being lifted for demand turn-up events specifically, allowing much larger aggregate response from enrolled assets.
Why Demand Turn-Up Is Getting More Important
The curtailment problem and the demand turn-up opportunity are two sides of the same coin. As the UK’s offshore wind capacity has grown, so has the frequency of periods where generation exceeds real-time demand — particularly overnight and on weekends in spring and autumn. National Grid ESO has been paying wind farms to switch off during these periods, with constraint costs running to hundreds of millions of pounds annually.
Demand turn-up offers a partial alternative: instead of paying generators to switch off, pay consumers to switch on. The electricity gets used rather than curtailed, and participants receive payments that reflect the value to the system. In practice, the loads most suitable for demand turn-up are those that are flexible about when they run but need to run a certain amount within a given period — electric vehicle charging, heat pump operation, battery storage charging, hot water cylinders, and industrial process heating.
The economics work because these loads are genuinely agnostic about exact timing. A home battery doesn’t care whether it charges at 2am or 3am. A heat pump running in mild weather can pre-heat the house an hour earlier than strictly necessary. A commercial refrigeration system can run its defrost cycle when excess generation is available rather than on a fixed schedule.
How the FCL Removal Changes Participation
The Flexibility Compliance Limit was set at a relatively conservative threshold per flexibility event — limiting total enrolled device response to prevent unintended grid effects. For demand turn-up specifically, this cap has been identified as unnecessarily restrictive. Because devices are being asked to increase consumption, not reduce it, the synchronisation risk profile is different from the demand reduction case. If enrolled devices ramp up consumption simultaneously, they’re helping absorb generation that would otherwise be curtailed rather than creating a spike on an already-stressed system.
Removing the FCL for these events allows aggregators to enrol significantly more devices and respond at scale. For the trial period running from November 2026 through February 2027, National Grid ESO will be collecting detailed data on response magnitude, timing accuracy, and any secondary effects on local distribution networks.
Participants — whether households via energy supplier platforms or businesses through commercial aggregators — won’t notice the regulatory change directly. What they may notice is more frequent turn-up events during the winter, and correspondingly more payments.
Who Can Participate and How
For households, participation typically happens through an energy supplier or flexibility platform that has enrolled their smart devices. The major routes currently include Octopus Energy’s Saving Sessions and similar platform, British Gas’s PeakSave programme, and several third-party aggregators including Kaluza, Flexitricity, and Upside Energy. Devices need to be grid-responsive — meaning either smart-controlled directly or connected via a compatible smart home integration.
Heat pumps from several manufacturers (Mitsubishi, Samsung, Vaillant, and others with Demand Side Response-compatible controllers) can participate directly. EV chargers with smart functionality and home batteries with grid export/import capability are similarly eligible. A home hot water cylinder with an immersion heater and a compatible smart controller can participate at low cost and with minimal installation complexity.
For businesses, demand turn-up is available through commercial flexibility contracts. The economics scale well — a commercial refrigeration operator or a manufacturer running process heating has significantly more flexible load available than a household, and payment rates reflect that value.
The Bigger Picture: Flexibility as a Grid Balancing Tool
The winter 2026 trial is being watched closely because it represents a test of whether demand flexibility can genuinely substitute for curtailment payments at meaningful scale. If enrolled capacity in the trial can reliably absorb 500MW or more during excess generation periods, that’s a number that starts to make a dent in constraint costs.
The longer-term trajectory points toward a more continuous flexibility market — one where smart devices are permanently enrolled and responding in real time to grid signals, rather than participating in discrete events. National Grid ESO’s ongoing work on the Centralised Interim Demand Turn-Up (CIDTU) mechanism is moving in this direction, though full implementation remains some years away.
For now, the winter trial gives households and businesses a concrete opportunity to participate in grid balancing — and get paid for it. If your EV charger, heat pump, or battery isn’t enrolled in a flexibility programme, it’s worth asking your energy supplier whether that option is available.