On 23 June, with temperatures at 34.6 °C, Britain's grid had its most uncomfortable evening in years. From eight in the morning actual demand ran above NESO's forecast; by late afternoon the error exceeded 1,500 MW — more than the 1,400 MW of reserve the operator is obliged to hold against the loss of its single largest infeed. Between 18:51 and 20:03 that evening, grid frequency dropped below the 49.8 Hz operational limit again and again: 48 minutes in total in Elexon's frequency record, touching 49.66 Hz. NESO curtailed exports to France and the Netherlands rather than issue a formal margin notice. The aftermath — an independent review, and allegations that the closeness of the call was played down — is still running.
Dispatches has covered this day before: The Night France Saved the British Grid told the control-room story, I went looking for a grid cover-up. I found something worse. verified the frequency record against an independent meter, and We built a power grid to watch winte…