About & methods
How the figures on Grid Stress are worked out, where the data comes from, what the X account posts, and where the data runs out.
Data sources
Everything comes from public, free data. Grid Stress doesn't use any private or paid feeds.
- Elexon BMRS: generation by fuel type and interconnector (every 5 minutes and half-hourly), system frequency (every 15 seconds), demand and NESO's demand forecast, the wholesale market price, Balancing Mechanism plans, instructions and settlement, and NESO's system warnings.
- NESO data portal: estimates of wind and solar on local distribution networks, which aren't metered centrally in real time.
The site refreshes every 5 minutes. Figures are only as current as Elexon's publication: most live data lags real time by a few minutes, and some settlement data by about 20 minutes.
Headline figures and the flow diagram
- Generation is fossil fuels, renewables and other sources (nuclear, biomass and other) from the latest 5-minute data, plus NESO's estimate of wind and solar on local networks.
- Transfers are interconnector flows plus pumped storage. Negative means exporting, or pumped storage charging.
- Demand is generation plus net transfers, following grid.iamkate.com, which inspired this site.
- Gas peakers (OCGT) are open-cycle gas turbines, which start quickly when the grid is tight. Elexon reports them separately from other gas plant. Smaller gas engines on local networks also act as peakers but aren't reported separately, so they aren't included.
- Coal and oil aren't shown: Great Britain's last coal plant closed in September 2024, and oil-fired generation has been at zero.
- Price is the market index price for the latest half-hour with traded volume.
Interconnectors
Flows come from Elexon's 5-minute data for each of the ten links. Capacities are the published nominal ratings. A link carrying more than its rating is shown as over 100%, and a link out of service shows zero.
Margin notices
An Electricity Margin Notice (EMN) is NESO asking generators and suppliers for more spare capacity over the next few hours. It's an early warning, used a handful of times a year, and doesn't mean power cuts are likely. Grid Stress reads the period, the margin shortfall and the issue time from the wording of each notice, and groups a notice, its updates and its cancellation into one EMN. If NESO changes its wording and a notice can't be read, it's flagged rather than shown wrongly.
Grid stress
- Frequency should stay between 49.8 and 50.2 Hz in normal operation, and 49.5 to 50.5 Hz is the statutory limit. Time outside the normal band is counted from 15-second readings.
- Demand forecast miss compares Elexon's initial demand outturn with NESO's latest national demand forecast for each half-hour, published shortly before it. It measures short-notice accuracy, not the day-ahead forecast.
- Accepted offers are what NESO agreed to pay generators to increase output, from Elexon's indicative settlement stack. Prices are each unit's offer; final settled costs can differ after flagging and later adjustments, so treat totals as indicative.
- Gas peakers running hard means OCGT output of 500 MW or more, which happened on about a dozen days in the year to October 2026.
Wind farms
- Covers the wind farms registered in the Balancing Mechanism. Smaller farms on local networks aren't listed individually.
- Output now is an estimate: each farm's own plan for the current half-hour, or the lower level NESO has instructed when it's paying the farm to turn down. Metered output per farm is only published about a week later.
- Curtailment and payments come from Elexon's indicative settlement data. Payments are shown with their sign: farms with a positive bid price, often those on Contracts for Difference, pay NESO when turned down while market prices are high.
- The figures cover the turn-down side only. NESO usually also pays other plant, often gas in England, to replace curtailed wind; that cost isn't included here.
- Regions: Elexon leaves most large wind farms without a region, so each unit's region is inferred from its transmission loss factor, which Elexon sets by geographic zone.
The X account
The @gridstressuk account is automated. It checks every 5 minutes and posts a card when:
| Event | Rule |
|---|---|
| Electricity Margin Notice | When one is issued; updates and the cancellation follow as replies in the same thread. |
| Grid stress | Frequency below 49.8 Hz for 2 minutes or more in a day, or NESO emergency action. One thread a day. |
| Interconnectors near capacity | Imports over the links to Norway, Denmark and the continent at 90% or more of their combined 8.8 GW, on two checks in a row. At most once a day. The Irish links usually export, so they're excluded. |
| Gas peakers running hard | OCGT output of 500 MW or more on two checks in a row. At most once a day. |
| Daily snapshot | The grid at 18:00 UK time. |
Posts don't include links, to keep the cost of X's API down; this site's address is on every card and in the account's bio.
Limits and corrections
Grid Stress is an independent project, not affiliated with NESO, Elexon or any market participant, and isn't advice. Figures marked as estimates or indicative can differ from final settled data. The source code is kept in a private repository; if you spot something wrong, mention @gridstressuk on X.