In a webinar held on 12th February 2024, National Grid ESO announced a shift in the current 15-minute rule for battery energy storage to a 30-minute rule. This change is due to take place on 1st March 2024. The shift could triple the volume batteries compete for in the Balancing Mechanism, improving skip rates. However, it will also introduce some new challenges.
In the Operational Transparency Forum on 12th February, National Grid ESO announced that the planned implementation date was being pushed back to 11th March. They are seeking feedback on the change via emails to box.balancingprogramme@nationalgrideso.com.
To see more about this and other ESO changes affecting battery energy storage, head here.
The 15-minute rule is how battery state of charge is currently communicated to the control room
Battery operators currently submit Maximum Export Limit (MEL) and Maximum Import Limit (MIL) to the control room to communicate their available energy. These values are currently set based on the maximum power that can be delivered for 15 minutes. When a battery’s state of charge moves into the upper or lower bound of its available energy, MEL or MIL reduces.
As of 1 March 2024, MEL and MIL will change to represent the maximum power that can be delivered for 30 minutes.
Change announced ahead of the launch of Balancing Reserve
The new Balancing Reserve service is due to launch on 12th March 2024. This will contract ‘regulating reserve’. These energy actions help balance generation and supply imbalances at longer timescales than frequency response actions.
Many of these actions are 30 minutes long, and the service requires contracted assets to deliver dispatches of this length. MEL and MIL will also be used to monitor availability and measure service performance.
This introduces a challenge with batteries performing the service. The 15-minute rule means the control room can only dispatch them for up to 15 minutes at a time. Additionally, their energy availability for 30-minute dispatches wouldn’t be able to be measured via MEL and MIL.
The move to a 30-minute rule solves these problems for batteries wanting to compete in the new service.
The change could start to solve a key cause of skip rates
The majority of energy dispatched in the Balancing Mechanism is for actions longer than 15 minutes in duration, with 30 minutes being the most common dispatch duration. The 15-minute rule has, therefore, limited the actions that batteries can be dispatched for.
In the first half of 2023, 76% of energy dispatched in the Balancing Mechanism was longer than 15 minutes in duration.
The shift to a 30-minute rule means that batteries should be able to compete for a much larger pool of Balancing Mechanism dispatches.
The change will introduce some challenges - and some new problems
The change to a 30-minute rule will unlock additional dispatch volume for batteries but it also has some consequences:
- All operators must adjust their MEL and MIL calculations and data submissions as of 1st March.
- The total power available from batteries in the Balancing Mechanism will also reduce due to this change. This is because batteries spend more time inside the 30-minute upper or lower bounds of energy than for a 15-minute bound.
- Shorter duration systems, less than 1 hour in duration, may find themselves coming out worse following this change. They will be able to provide their full availability in the Balancing Mechanism much less regularly.
This is a temporary change until the conclusion of GC0166
National Grid ESO opened a proposal for a new Grid Code change in November: ‘GC0166: Introducing new Balancing Programme Parameters for Limited Duration Assets’. This aims to find a long-term solution for communicating battery state of charge with the control room.
The Grid Code modification should be implemented later this year, alongside changes within the Open Balancing Platform. This will allow batteries to be dispatched for longer durations whilst also avoiding the downsides of the current methodology using MEL and MIL.
Elsewhere, actions are being taken to enhance the use of bulk dispatch for batteries
In the webinar, National Grid ESO talked through other changes that have been taking place, or are due soon.
- Independent analysis for the ESO on skip rates is due at the end of February and is expected to be published in March.
- 75% of battery instructions are now taking place via the OBP, representing 50% of dispatched energy.
- Scheduling improvements have been made for battery energy storage. This includes a better estimate of the future availability of batteries.
- An additional balancing engineer has been added to the control room to assist with using the Open Balancing Platform and bulk dispatch for batteries. This is for an initial three-week period, starting from February 5th.