What does the GB power outage on 9 August 2019 tell us about the current state of decarbonised power systems?

The GB power blackout, that happened on 9 August 2019, was a unique stress test exposing fault lines brought about by the rapid changes due to the decarbonisation drive and penetration of smart grids technologies. It has demonstrated that, as a significant amount of new equipment and controls were added to the system in a very short time, the probability of common, hidden modes of failures has significantly increased. In the face of declining reliability, maintaining the status quo is not an option. While currently increasing the (N-1) security margin could prove to be expensive, the balance of costs and benefits is likely to change in future. Especially wider application of innovative frequency controls, including "virtual inertia" and Remedial Action Schemes, could help reduce the costs. Distributed Generation (DG) reached such a high penetration level that it cannot be treated any longer as negative demand. Traditional under-frequency load shedding should be made more selective. Interactions between the power system and other infrastructures are still poorly understood and there is a significant risk that if the current compartmentalised approach to their governance and operation is not changed, we may see more unexpected consequences of disturbances across the whole system.