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?
- 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.
Since the launch of Balancing Reserve, 42 different battery BMUs have participated in the service. This is 77% of all Balancing Mechanism-registered battery units.
However, contracted units have not yet received dispatches much different from those uncontracted systems. 24% of dispatch volume has been from instructions greater than 15 minutes for both contracted and uncontracted systems.
82% of all Balancing Mechanism volume is dispatched through longer instructions
In the last two weeks, batteries have accounted for 32% of dispatch instructions in the Balancing Mechanism. Most of these are very short, sent via bulk dispatch. However batteries do now account for the majority of 10-minute, 15-minute, and 20-minute instructions.
Batteries only made up 1.4% of instructions 30 minutes or longer, however. These actions (including ramping) represent where most energy is dispatched in the Balancing Mechanism. 62% of this is system flagged. This includes turning wind down to manage constraints or increasing CCGT output for inertia purposes.
In the last two weeks, battery dispatch volume has accounted for 3% of all Balancing Mechanism dispatch volume. CCGTs received the bulk of this, 53%. Meanwhile wind received 28%, of which almost all is for system-related reasons.
Three-quarters of batteries had switched to the 30-minute within five days
During the two-week transition periods battery operators could submit availability data signalling either 15 minutes or 30 minutes dispatch capability. They were to notify the control room ahead of making the switch. As of March 25th, all submissions should now be calculated based on the 30-minute rule.
Within 5 days, 75% of BM-registered batteries had been dispatched for longer than 15 minutes, indicating they had made the change. This covered 11 out of 13 different battery operators. As of 24th March, 87% of systems had done so.
Batteries in Scotland have received the most instructions longer than 15 minutes
Batteries in Scotland have led the way with longer duration dispatches, with the four systems with the most dispatches greater than 15 minutes north of the border. Of these instructions, 82% were system actions - Bids made during a period of constraint.
Across all dispatches during the period for these batteries, system-flagged actions made up 43% of dispatches. This indicates that system-flagged actions are biased towards longer dispatches, and so the 30-minute rule change could mark a shift in how batteries are used for system-flagged actions.
Following the end of the transition period dispatches may change yet again
During the transition period, Balancing Mechanism dispatches have been made through a combination of bulk dispatch and legacy dispatch tools. This is because bulk dispatch has only been used for dispatches of 15 minutes or less.
As of 25th March, bulk dispatch will be used for most battery dispatches. This means how batteries are dispatched could change yet again. Longer instructions will only be sent by bulk dispatch if grouped instructions are required to cover a longer period. This means the distribution of dispatches will likely change again.