National Grid ESO’s new Downward Flexibility Management service was brought into play this weekend to cut embedded generation, along with the Grid Code modification which was also approved.
The ESO’s modification to the Grid Code clarified its ability to disconnect embedded generation in emergency events and was approved by Ofgem last Thursday (7 May).
The modification had already been deemed urgent by the regulator, allowing for it to be implemented ahead of the bank holiday the following day, with the ESO concerned the day could have seen particularly low demand and “significant operational risk”.
However, National Grid ESO told Current± it had not needed to use the Grid Code modification to disconnect embedded generation. It did, however, cut embedded generation through its voluntary Downward Flexibility Management service. The service was unveiled last week and offers small-scale renewable generators commercial contracts to reduce or completely switch off their output.
Whilst the ESO confirmed to Current± the service had been used, it did not confirm any figures. Speaking to this publication, energy tech firm Limejump said that up to 238MW of embedded generation was requested to shut down between 4am and 7am yesterday 10 May, adding that this was most likely to have been wind generation.
Limejump itself has signed up to the new service, although it did not participate this weekend. However, it said it will provide up to 300MW turn down over at least a three-hour period if called upon.
Why National Grid ESO didn’t need to disconnect embedded generation without warning was likely a combination of several factors, according to EnAppSys, one of which was the level of wind generation.
It was forecast at the beginning of the week that there would be large amounts of wind generation, however as the week progressed the timing of the wind peak shifted from "the middle of the night into early morning," Phil Hewitt, executive director of EnAppSys explained to Current±.
"That helped National Grid, I think, as they didn’t have to manage the lowest demand with the maximum wind. The wind arrived around three hours afterwards so it wasn’t as extreme of an event as it could have been," Hewitt said, adding that this meant demand wasn't as low as expected.
This is due to some of that wind being embedded generation, which National Grid ESO classes as demand as it is connected to the distribution network.
Another element that may have helped was the market coupling mechanism resolving, Hewitt said, which meant there was less interconnection during the period.
“The interconnectors had dispatched slightly differently, so it wasn’t as big an impact having to reverse interconnectors,” Hewitt added.
The ESO has outlined a number of measures it is taking to ensure grid stability as demand stays low due to the COVID-19 lockdown, including both the new service and the Grid Code modifications that remain valid until October.
It has also signed a contract with EDF for the Big Six supplier to halve the output of its Sizewell B nuclear generator during the period of low demand.
This weekend also saw Britain mark a major milestone, going coal-free for a month for the first time since the Industrial Revolution, due to the low demand and the high levels of renewables on the grid.