Unit Imbalances

About

The Unit Imbalances chart replicates the Unit Bid/Offer Prices chart, but plotting levels of imbalance (max, average during imbalances and average real) for a given unit or filter group.

Included Data

The data on this chart is as follows:

• Capacity - The nameplate capacity of the unit - ie if at 100% availability.
• Max Imbalance - The highest imbalance level that occurred in the period.
• Av Imbalance Size - The average size of imbalance levels when they were non-zero in the period.
• Imbalance - The average level of imbalance in the period (being reduced by zero values when imbalances were not occurring).
• Trip Frequency - The frequency of periods of imbalance (counting 1 as a period from imbalance volume being >0 until the period when the imbalance volume returns to zero.
• Start Trip Frequency - As with the Trip Frequency, but only recording trips when a start has also occurred in the period up to 3 hours before the trip begins.

The imbalance volume is calculated as the maximum of zero and the generation subtracting the availability, ie the levels of generation that cannot be achieved because of insufficient availability.

The availability figure used is the Max Export Limit availability data (the maximum level at which the BM Unit may be exporting to the GB Transmission System at the Grid Supply Point), with units having an obligation to re-declare their Max Export Limit (MEL) whenever their availability reduces (for instance after a failed start).

The generation figure used is the levels of post-balancing generation after National Grid has adjusted generation within gate closure.

Data Service

The Unit Imbalances data can be extracted from the API to extract on a monthly basis the imbalance levels. The parameters used as follows: