28 Mar 2024
Wendel Hortop

30-minute rule: How have Balancing Mechanism dispatches changed

On March 11 2024 the way in which battery energy storage systems communicate their energy availability in the Balancing Mechanism changed. This is through a move to the ‘30-minute rule’, which would allow batteries to be dispatched for longer.

Battery dispatches had effectively been limited to 15 minutes due to the ‘15-minute rule’. This is via the data the control room sees about a system’s state of charge - their MEL and MIL. As of 11th March, this changed to the ‘30-minute rule’ through a two-week transition period. As of 25th March, all submissions must now be following the ‘30-minute rule’.

But what has been the impact on how batteries are used in the Balancing Mechanism?

Wendel digs into the impact of the transition to the 30-minute rule
  • Longer dispatches for batteries are happening, with 12% of these longer than 15 minutes during the transition period
  • These longer dispatches have been instructed manually instead of via bulk dispatch. As of 25th March, bulk dispatch will be used for most instructions again.
  • The overall dispatch volume for batteries in the Balancing Mechanism has not yet increased.
  • Batteries in Scotland have received the most dispatches longer than 15 minutes, through a large number of system-flagged actions.
  • 82% of all Balancing Mechanism volume during the period was dispatched through instructions of 30 minutes or longer. 62% of this volume is system-flagged.

Dispatches are now longer on average - but still behind where they were in January

The average duration of dispatches has risen since March 11th, now averaging 8.1 minutes, compared to 6.5 minutes in the two weeks prior. This is the highest average dispatch duration since the launch of bulk dispatch for batteries in January.

The change to bulk dispatch significantly reduced the duration of dispatches for batteries on average, by over 50%. This is because of a shift to a larger number of very short, mostly one-minute-long dispatches.

Following the start of the transition period (actually the day prior), batteries began to see an increased number of instructions longer than 15 minutes.

Some Balancing Mechanism actions did last longer than 15 minutes prior to the change. This is due to two main reasons. Firstly, through data and instruction errors. Secondly, bulk dispatch can actually send batteries longer-duration dispatches if this adheres to the energy they declare available. For example, being instructed for 5 MW, while declaring 50 MW available.

The distribution of dispatch length for batteries keeps on evolving

The type of dispatch batteries receive changed significantly with the introduction of bulk dispatch. The number of instructions being sent to batteries quadrupled. However, a third of the instructions were just one minute in length, causing a reduction in the average length of BM dispatch.

During the transition period to the 30-minute rule, a lower proportion of instructions have been one minute long. 12% have been greater than 15 minutes, with a high number of 20-minute dispatches. These now represent 3% of all battery dispatches.

The distribution reflects how these instructions are being made. Prior to March 11th, almost all dispatches were made via the bulk dispatch tool. This created many one-minute dispatches, with others adhering less to the five-minute buckets common before.

During the transition period, longer instructions have been sent via legacy, manual dispatch tools. This likely explains the high number of instructions exactly 20 minutes long, and the fall in one-minute dispatches. As of March 25th, bulk dispatch is being used to create and send almost all battery instructions again.

On an energy basis, dispatches longer than 15 minutes now represent 25% of battery BM volume. This is up from 8% in the period from February 1st. Overall dispatch volumes for batteries haven’t yet increased, however.

No impact yet on dispatch duration from Balancing Reserve contracts

One of the main drivers of the change to the 30-minute rule was the launch of Balancing Reserve on March 13th. This requires up to 30 minutes of response from those contracted, which previous availability data could not guarantee.