IN Brief:
- Reported internal concerns focus on modelling, forecasting, and operational visibility.
- Frequency remained within statutory limits throughout the June event.
- Ofgem and an independent legal review are examining separate aspects of system operation and governance.
Engineers at the National Energy System Operator have reportedly raised internal concerns over forecasting, system visibility, and the tools available to the electricity control room during increasingly complex operating conditions.
The concerns emerged after tight system conditions during the week beginning 22 June, when high temperatures, low wind output, reduced gas-generation availability, adverse interconnector flows, sustained demand, and network constraints affected Great Britain and neighbouring systems.
Areas raised internally are understood to include the modelling of generation and demand, visibility of distributed resources, and the use of different forecasting methods across operational teams. They remain allegations and have not been established as findings by the continuing independent and regulatory reviews.
No customer demand was disconnected during the June period, while system frequency remained within the statutory range of 49.5Hz to 50.5Hz. A recorded low of 49.66Hz and high of 50.23Hz moved outside NESO’s narrower normal operating guideline of 49.8Hz to 50.2Hz at points, but did not breach statutory limits.
Control-room actions included market engagement, reserve deployment, demand flexibility, trading with neighbouring system operators, and instructions to interconnectors. Electricity margin notices were issued as part of the response to reduced available headroom.
Visibility changes as the system decentralises
Traditional system models were developed around a smaller number of large generators connected directly to the transmission network, whereas current operation involves growing volumes of distribution-connected solar, batteries, flexible demand, electric vehicles, and smaller generating assets.
Many of those resources are not visible to the national control room with the same granularity as transmission-connected plant. Aggregate forecasts can estimate their combined contribution, but weather, customer behaviour, local network conditions, and market dispatch can alter the net position.
Forecast errors become more material when available margins are already narrow or several adverse conditions occur together. A modest deviation in renewable output, demand, or generator availability can require a substantially different balancing response if the system has little spare headroom.
Interconnector behaviour adds further uncertainty because cross-border flows respond to prices and system conditions in several markets. An assumed import can reduce or reverse where neighbouring countries experience the same weather conditions or face their own plant and network constraints.
Control-room systems must combine those forecasts with real-time measurements, reserve availability, network limits, and the technical characteristics of connected resources. Decisions depend on data accuracy, model performance, operator judgement, and clearly defined escalation procedures.
Reviews must separate evidence from allegation
Ofgem’s independent review of the June heatwave event is examining system and market performance, including the circumstances surrounding the operational notices issued during the week.
An additional investigation led by Eversheds Sutherland is reviewing decision-making and record-keeping. Its scope is distinct from the technical post-event work, although operational evidence and governance arrangements may overlap.
The existence of internal concern does not establish that the system was outside control or that customer disconnection was imminent. Published frequency data show that statutory limits were maintained, while operational notices provided a mechanism for increasing available capacity and managing risk.
Remaining within those limits does not remove the need to examine how accurate the forecasts were, what visibility operators possessed, and whether available tools represented system conditions adequately. Post-event analysis is intended to identify technical or procedural weaknesses before they contribute to a more serious event.
Attention is likely to fall on data from distribution-connected resources, assumptions around generation availability, reserve procurement, interconnector schedules, and the records used during operational decisions. Recommendations could involve software, modelling, data exchange, operating procedures, governance, or several of those areas together.
As the power system becomes more decentralised, diversity can strengthen resilience when assets are observable, controllable, and accurately represented. Weak data or fragmented control arrangements can reduce that benefit.
Firm conclusions will depend on the independent evidence, including what information was available, how it was interpreted, which actions were taken, and whether technical or procedural changes are required.
