Neso's Inertia Cut Trades Blackout Risk for Balancing Savings, Analyst Warns
Montel EnAppSys warns Neso's plan to lower inertia thresholds cuts balancing costs but sharpens Britain's exposure to grid frequency failures.
Britain's National Energy System Operator is proposing to reduce the level of inertia maintained across its power system, a move that Fintan Devenney, senior analyst at Montel EnAppSys, said on Monday (2026-08-10) "will increase the risk of blackouts." Devenney was responding to a report in The Times disclosing the proposal.
The same analyst acknowledged the commercial case. "This move should allow more wind onto the system and reduce overall balancing costs, potentially saving the consumer money," Devenney told Montel. But the two positions sit alongside each other rather than cancelling out — the cost benefit is real, and so is the stability risk.4
Inertia in AC power systems comes primarily from large synchronous generators — gas turbines, nuclear reactors — whose rotating mass resists instantaneous frequency deviations. As Britain displaces those assets with wind and solar, electronically rather than mechanically coupled to the grid, that buffer shrinks. Reducing the mandated inertia floor means disturbances can push frequency outside safe operating ranges faster, before automatic protections can respond.4
A leaked report commissioned by Neso from consultancy Cornwall Insight, made public on July 27 (2026-07-27), already warned that Britain's net zero buildout risks leaving households with higher electricity bills and the grid more susceptible to blackouts, according to oilprice.com. The inertia proposal falls within the category of choices that report flagged as carrying those risks.4
Neso has faced sustained pressure over system costs. At a parliamentary committee hearing on July 8 (2026-07-08), Energy Voice reported that Neso chief executive Fintan Dixon was pressed on whether the operator's actions would prevent constraint costs from reaching £8 billion by the end of the decade. Dixon committed only to reducing "the costs it could influence" — stopping well short of the figure MPs had put to him.3
A separate operational lapse compounded the picture. Montel reported on August 5 (2026-08-05) that Neso's rapid green generation buildout had stretched its capacity "to keep up," citing a case in which 818 meters had been installed backwards. It is a distinct issue from inertia management. Yet it points to the same institutional pressure: a system operator scaling faster than its processes have adjusted to.5
Ofgem has also flagged conduct concerns in adjacent markets. The regulator found instances of capacity auction bids submitted at extremely high prices, well above imbalance levels subsequently observed, raising concerns about market manipulation inflating Neso's balancing costs — the very costs the inertia reduction is partly intended to lower, Montel reported in May (2026-05-21).1
Devenney's assessment reflects a straightforward engineering trade-off: a leaner inertia buffer reduces costs under normal operating conditions but widens potential damage when conditions are abnormal. Britain's grid has been moving in this direction for years as fossil fuel plant retires. Neso formally proposing to lower the floor is a step beyond the incremental drift that has characterised the transition so far.4
NESO's summer outlook published in June (2026-06-03) projected Great Britain to be a net electricity importer under both high and low gas price scenarios, relying on about 1.4 GW of interconnector flow from Northern Ireland while links including Viking Link handled surplus periods. A grid carrying reduced inertia while drawing heavily on interconnectors carries additional exposure to disturbances originating on partner systems during peak import windows.2
A formal consultation, if Neso proceeds to one, would require the operator to publish probabilistic loss-of-load figures alongside projected balancing savings — numbers that Devenney's Monday (2026-08-10) warning left unquantified. How Neso's own modelling compares with Cornwall Insight's assessment, and how Ofgem responds to any published risk disclosure, will shape this argument into the autumn.4,3