The sudden loss of nearly 2GW of generation triggered a stress event and power cuts experienced up and down the country on Friday evening (9 August 2019).
The incident, which caused significant disruption up and down the UK, was triggered by failures at two large generators, specifically Orsted’s 1.2GW Hornsea offshore wind farm and the 727MW Little Barford gas-fired power station in Bedfordshire, operated by RWE.
Those failures triggered a stress event which saw the transmission grid’s frequency drop to 48.91Hz, far below the 49.5Hz threshold, causing the power cuts experienced by consumers.
Commenting on the incident, National Grid ESO described the simultaneous loss of two large generators as “rare and unusual”, and said the system operator was working with the parties involved to understand its causes.
Other generators responded to the event by ramping up their own output, but National Grid ESO said that due to the scale of generation lost - just shy of 2GW - the response was not sufficient to cover it and as a result, selected demand across the country was disconnected to protect the system itself.
The incident itself lasted less than 15 minutes and distribution network operators (DNOs) were given the all clear. All demand was reconnected by 17:40.
“We appreciate the disruption cause and will continue to investigate, with the generators involved and wider stakeholders, to understand the lessons learned,” a statement issued by National Grid on Friday ESO read.
But the issue could prove costly for National Grid ESO, with the system operator now facing a potential fine of up to 10% of its annual turnover should it be found to have been at fault.
While incidents such as these are rare, the power sector has nevertheless responded by arguing the power cut was evidence of the need for greater quantities of flexible generation, especially as the penetration of variable renewable power increases.
“These risks will only be balanced by the introduction of high-speed, grid connected electricity storage distributed across the country, and delivered at scale. It’s vital that the National Grid, local grid companies and battery storage operators work together to ensure that events like this afternoon’s power cut do not become commonplace.
“We thought we would be waiting for a cold winter for the impact of intermittent renewables to strike – however unwelcome, this is just another milestone in the energy transition from fossil fuels to renewables. It demonstrates with great clarity the urgent need for electricity storage at scale on the UK’s grid,” Mark Simon, chief executive at battery storage firm Eelpower, said on Friday evening.
Steve Shine, executive chairman at Anesco, echoed Simon’s sentiments, adding that the blame of for the power cut lied “squarely at the door of National Grid” which had “failed to take appropriate preventative action”.
“There has never been a clearer example of the vital role of storage for the grid. As more and more renewable generators come online and we drive towards ‘net zero’, such assets need to be effectively utilised and proper frameworks put in place to work with operators,’ Anesco’s asset management director Mike Ryan added.