On the evening of 23 June, Great Britain came closer to the edge than on any other night this summer.
On NESO's official numbers, national de-rated margin fell to 4.1 GW — the tightest evening of the summer. Frequency sat below 49.8 Hz for 48 minutes between 18:51 and 20:03, bottoming at 49.656 Hz. At 20:01 NESO requested Emergency Assistance on an inter…