The Week in Flexibility: National Grid is Buffeted by an Imperfect Storm of Factors

Each week, we take a look at the week in flexibility trading that has just been, and a look at what’s next. Enjoy our latest instalment: That was a Friday we won’t forget in a hurry.

A gas-fired power station at Little Barford, Bedfordshire, tripped at 16:53, followed by the Hornsea offshore wind farm disconnecting from the grid. Frequency fell quickly to 48.8Hz, a figure not seen since 2006 and well outside of the National Grid operating parameters. This event was exacerbated by the 11GW of wind generation in use, equating to 32% of demand at the time turning off. Due to these actions, the grid was low in inertia and unable to cope with the drastic drop in frequency.


Widespread blackouts followed as automatic load shedding started to protect the system across the midlands, the Southeast, Southwest, Northwest and Northeast of England, and Wales. It is estimated to have affected over a million people with trains, traffic lights, airports, hospitals and residential customers losing power.


The load shedding actions means that the Net Imbalance Volume (NIV) in the Balancing Mechanism didn’t surpass 300MW. This is in stark contrast to the previous day when Peterhead Power Station tripped (a similar-sized unit that and tripped at a similar time) when frequency only deviated by 0.2HZ 49.8Hz which is not low enough to trigger any failsafe response mechanisms (e.g. Static FFR at 49.7Hz or load shedding at 48.8Hz. This ironically meant that the market felt the impact of the previous day’s trip much more than the events that lead to Friday’s blackouts due to demand not being taken out of the system. The key difference between the two days was the amount of wind, on Thursday it was below 2GW whereas on Friday there was 11GW running at the time.

An Ofgem investigation is now to follow these events, and all eyes will be on the findings delivered and could drive changes to balancing services.

We will be releasing some further analysis of this event later this week so look out for that.

Against this busy Friday backdrop, it’s important we take a moment to celebrate the national wind record falling, with wind generating at over 13GW across the morning peak on Friday. High wind generation overnight meant that wind was supplying over 50% of demand for some periods.

There were a few notable events earlier in the week that deserve mention too.

On Wednesday, National Grid was short on a majority of the morning settlement periods due to higher wind outturn than forecast, reaching 6GW on average and System Price fluctuated around the £22/MWh mark during the day.

Wind outturn sat at 1 to 1.5GW above the forecast and dropped to reach 1.1GW. In response System Price fluctuated between £60 and £66/MWh from the early morning National Grid compensating during this period by instructing Gas, batteries (including Limejump assets) and hydro assets such as Dinorwig, at prices between £72 and £80/MWh.

Last Monday Wind staked a claim as a significant part of the generation mix as output rose to 6GW, pushing System Price down, as the gird was oversupplied with energy for most of the day.

Flex in numbers:

  • Total number of instructions for Limejump: 181
  • Top System Price of the week: £80
  • Lowest System Price: £4

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