The cost of keeping the lights on, and switching the wind off.

NESO publishes two different totals. The audited accounts give one, and its Annual Balancing Cost Report gives an operational total built from cost categories. They differ every year, sometimes up and sometimes down, so we chart them separately and never splice them. The operational series is longer and already includes FY2025-26.

When the transmission network can’t carry power from where it’s generated to where it’s needed, NESO pays some generators to turn down and others to turn up. The first chart uses NESO’s report workbook. The second rebuilds the same costs from NESO’s daily data as a cross-check. The two agree within a fraction of a percent, and the coverage report lists the gaps.

NESO’s own figures for how much wind it paid to switch off, and what share of potential wind output that was.

An Electricity Margin Notice is NESO asking the market for more spare capacity because margins look thin. It is not a blackout. We count incidents, not messages: each incident has an initial notice, usually some updates, and a cancellation. Elexon’s API only goes back to May 2023, so we start the count there.

How close NESO’s day-ahead forecast of national demand came to what actually happened. Forecasts are typically published about a day before delivery, and each is matched to its own issue time. National demand excludes embedded solar and wind, which NESO can’t meter directly. Their growth makes the job harder, and so does the weather.

Different units can’t share an axis honestly, so both series are indexed to the same base year. Complete financial years only.