BSC Insights: Using the Insights Solution to predict Capacity Market Notices

In this BSC Insight, Angus Fairbairn outlines how you can use forecast data from the Kinnect Insights Solution to monitor generation, demand and margins preceding events on the GB Electricity System. He does this through the lens of the summer 2022 heatwave and the resulting Capacity Market Notices (CMNs).

Hot weather in 2022 causes CMNs to be issued

On 18 and 19 July 2022, the UK had its first ever red warning for extreme heat issued by the Met Office as temperatures exceeded 40°C in parts of England. This was during an ongoing heatwave, which was also accompanied by a lack of wind and rainfall. Further amber heat warnings were issued between 9 and 11 August. 

The elongated period of extreme temperatures placed pressures on the GB electricity system that had not been seen before during summer in GB. This contributed to three CMNs being issued.

What are Capacity Market Notices? 

A Capacity Market Notice (CMNs) is an automated signal given in advance of an event where the National Grid Electricity System Operator (NGESO) predicts that there may be less generation available than it expects to need to meet national electricity demand on the transmission system. This takes into account additional operational reserve requirements. The notices are intended to be a signal that the risk of a System Stress Event in the GB electricity network is higher than under normal circumstances.

A System Stress Event is a Demand Control Event, which is a forced demand reduction or disconnection from the ESO triggered by a national shortage of generation resource. 

A CMN is different to an Electricity Margin Notice, which are also issued by NGESO.  

Under the rules of the Capacity Market, Capacity Providers are only needed to generate during a System Stress Event. 

CMNs in the 2022 heatwave 

National Grid ESO issued three CMNs over two days this summer, the table below details these notices. 

CMN Publish Date Publish Time Settlement Date Settlement Period Event Start Cancel Time Cancelation Issued at
CMN 1 18 July 2022 14:34:00 18 July 2022 41 19:00:00 19:00:00 15:05:00


18 July 2022 15:34:00 18 July 2022 43 20:00:00 20:00:00 19:51:00
CMN 3 11 August 2022 13:34:00 11 August 2022 39 18:00:00 17:30:00 17:05:00

All of the issued CMNs were cancelled before the Capacity Market event commenced. NGESO tweeted along with the cancellation that they were confident there was enough supply to meet demand. Despite NGESO cancelling the notices, CMNs provide a signal that there may be a shortage of generation compared to expected demand on the Transmission System. 

The only previous CMN in the BSC Summer Season (1 June to 31 August) was on 20 June 2017. This notice was also cancelled prior to the event. 

How did generation forecasts change leading up to the CMNs? 

Elexon’s Insights Solution has a selection of datasets for which provide forecasting data on GB electricity generation and demand from the ESO. The datasets provide an outlook for the GB electricity system up to three years in advance of a Settlement Day. 

In this Insight article, the Output Usable forecast by Unit (UOU) has been used to look into the changes to generating in the two weeks leading up to the 18 July and 11 August heatwaves. The UOU forecast is based on planned outages across all BM Units.  

The July heatwave 

The graph below displays the Fuel Types that saw the most change in the two weeks leading up to the CMN events. This is because for the 18 July 2022, all Fuel Types in the UOU forecast remained stable apart from Combined Cycle Gas Turbine (CCGT), Wind, Coal and Biomass units. You can use the drop-down filter at the top right of the graph to see forecasts for specific generation units within the Fuel Types.

Electricity from CCGT sources is the main source of generation for GB Electricity, responsible for around 43% of Transmission System generation in 2022. The expected delivery of power from this Wind and Biomass expected generation also dropped in the UOU forecasts. Wind from 3,707MW on 11 July to 2,046MW on 15 July and Biomass from 3,413MW on 4 July to 2,997MW on 16 July.  

When these fuels are not expected to deliver enough generation, NGESO may look to Coal to cover electricity demand. However, this fuel also saw a drop in expected output in the two weeks leading up to the CMN from 2,320 on 6 July to 1,020 on 16 July. 

The August heatwave 

The graph below shows the forecasted generation for Nuclear, CCGT and Wind Fuel Types from the UOU dataset. These were the only Fuel Types to see significant changes leading up to the day where the third CMN was issued on 18 August.

On 11 August, there was a similar drop in CCGT output (from 22,761MW on 31 July to 22,162MW on 9 August) and some variations in the available wind generation. The main change in generation came from nuclear generation units, which typically have a very stable output. Nuclear output dropped from 5,519MW on 1 August to 4,766MW on 8 August and contributed to the CMN.

Using the Insights Solution to predict scarcity on the system 

In the day prior to a CMN event, Elexon’s Insights Solution provides more detailed forecasts. which show expected generation and demand at a Settlement Period (half hourly) resolution. These forecasts allow users to predict at what time in the day electricity may be scarce on the system. 

The Indicated Margin forecast takes the sum of Maximum Export Limits (MELs) from all BM Units, which is the maximum amount of generation available to the System Operator, and compares it to the National Demand Forecast. The lower the margin the scarcer the available generation is, and the higher the likelihood of a System Stress Event. 

The Indicated Margin forecast can be used to see how the margin value changed leading up to the time of the three CMNs that occurred on 18 July and 11 August. 

Average Indicated Margin in the July and August Heatwaves 

The graphs below show the evolution of the average expected margin for all of the Settlement Periods on both 11 August and 18 July. The first Publish Time of Indicated Margin for all Settlement Periods is at 11:00 on the previous day. The average expected generation for all Settlement Periods on both days saw large decreases in expected margins in the morning of the days prior to the CMN being issued. The average margin only considers the Indicated Margin for the days where CMNs were issued. When a forecast is published within these days, the average margin considers forecasted margins from one hour ahead of the forecast publish time to the end of that current day. For example, if the margin value is published at 12:00 on 18 July, the average margin will be from 13:00 to 23:30 on 18 July. 

Average of the Indicated Margin in the July Heatwave

The average Indicated Margin for Settlement Periods on 18 July saw a significant decrease from 22,256MW at 12:00 to 21,280MW at 12:30 on 17 July. Decreases in the average Indicated Margin continued until a low of 16,968MW at 18:00, one hour before the first CMN start time on this day. This can be viewed in the graph below. 

Average of the Indicated Margin in the August Heatwave 

On 11 August, you can also see a large decrease in the average Indicated Margin on the morning of previous day. There was an initial drop off of Indicated Margin from 21,777MW at 11:30 to 19,126MW at 12:30 on 10 August 2022. The decrease persisted until a low of average margin at 16,391MW at 16:00 on 11 August, two hours prior to the CMN start time for this day. 

The average Indicated Margin begins to rise as the peak time periods where margins were at their lowest on these days and are no longer considered in the average. 

Although CMNs were issued by NGESO in the afternoon of both dates, there were signs that the GB Electricity System was stretched prior to 11 August as shown by thein the Elexon Insights Solution Indicated Margin data. 

Data Sources used in this BSC Insight

All of Elexon’s Insights Solution data is published for free under the BMRS Open Data Licence. 


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