FAQs

There are two main sources of additional information that it is recommended market participants be aware of.

• System Warnings page on the BMRS website. This is where National Grid ESO communicates any operational warning messages with the industry. These include Electricity Margin Notice (EMN) (previously known as Notice of Inadequate System Margin (NISM)), High Risk of Demand Reduction (HRDR) and Demand Control Imminent (DCI).

• De-rated Margin values available on the BMRS website. These values follow a similar calculation to the Capacity Market Notice trigger and are communicated by National Grid ESO on a Day Ahead, 8hr, 4hr, 2hr and 1hr profile to give advance notice of potentially tight Settlement Periods on the Transmission System.

  When De-rated Margins were originally developed in 2015 the Calculation Methodology document essentially confirmed that where the DRM is 0MW at 1 hour out (Gate Closure) there is a 50:50 chance of available generation not being sufficient to meet demand during the relevant Settlement Period.

  Loss of Load Probability (LoLP) data is also shared on this page. In tight Settlement Periods you can expect LoLP data to change to a non-zero figure with the 1 hour forecast potentially influencing cashout prices.

Other information sources that may provide advance notice of a potentially tight Settlement Period include:

• 2-14 Day Ahead Surplus forecasts on the BMRS website show the daily peak half hour MW value of Generating Plant Demand Margin for each day from the 2nd to the 14th day following the current Operational Day and accounting for operating margin requirements (OCNMFD Surplus (SPLD))
• Day and Day Ahead Margins on the BMRS website show forecasts of indicated margin for each Settlement Period (MELNGC) within day and day ahead. This is the difference between any Maximum Export Limits (MELs) issued to National Grid ESO by generators and the National Demand Forecast.