In December, the ESO published new guidance for Balancing Mechansim-registered units (BMUs), particularly affecting battery energy storage assets. This provides the best practice for submitting MEL (Maximum Export Limit) and MIL (Maximum Import Limit) via EDT/EDL (the communication protocol for most BM-registered systems).
Why has this new MEL/MIL guidance been published?
The main aim of the update is to reduce unnecessary or useless information sent to the ESO to reduce overall data flows. It also clarifies how BMUs should declare power unavailable in the Balancing Mechanism when contracted for frequency response.
Every BMU tells the Control Centre the maximum power it can export and import via its MEL and MIL. For batteries, this represents the maximum power that can be provided for 15 minutes and is dependent upon state of charge. This is being reworked through the new Grid Code modification, GC0166.
The ESO has stated it would not currently enforce the guidance above but would monitor the data submissions.
The volume of data flowing to the control room is growing and has started to cause technical problems
The ESO has said it receives almost three times as many MIL/MEL data submissions from battery BMUs now than it did in January 2023. This has resulted in ESO and Elexon IT systems being stressed and causing delays in publishing data.
This has also started to lead to problems within the control room, so much so that ESO decided to procure zero Dynamic Regulation volume on October 14th. This is because the service can result in a high volume of MILs and MELs being continually sent to the Control Centre.
Five ways to cut down on MEL/MIL submissions
The ESO highlighted five different scenarios that are unnecessarily causing system stress:
- Duplicate records: the same information being sent on multiple occasions.
- Redundant records: sending information for the same period with no change.
- Unnecessary granularity: data being split into multiple settlement periods when it could be sent in one block.
- Unnecessary precision: highly precise data being submitted too far in advance.
- Bulk submissions: automatic submissions for multiple units being sent at the same time, rather than spread over the half-hour.
The ESO would like operators to streamline the data submissions sent as much as possible for scenarios 1, 2, and 3. The main change comes from not re-declaring MEL and MIL when there has been no change to the last information communicated to the Control Centre.
For scenario 4, the ESO highlighted that submissions beyond 30 minutes ahead are rarely useful because they are often overwritten. This is especially the case when the unit is performing frequency response, meaning its state of energy is likely to change. Therefore, these future submissions do not need the same accuracy as those within settlement period.
For scenario 5, ESO advised operators to spread out automated data submissions across a half-hour rather than sending them all simultaneously. For example, data submissions for ten units could be sent at minute intervals between 09:00 and 09:10 rather than all at 09:00.
Frequency response unavailability should be declared via MEL and MIL
When BMUs are stacking revenue from the Balancing Mechanism with frequency response services, they must declare power reserved for frequency response as unavailable. There are two methods currently used in the market. One is reducing the MEL/MIL by the contracted volume, the other is setting extreme prices (+£9,999/MWh) for the portion of capacity they want to reserve.
The ESO wants all providers to shift to using MEL/MIL to indicate what portion of power is unavailable due to the contracted frequency response.
Bid/Offer levels can only be given half-hourly and are relative to FPN. This can cause problems when batteries are ramping with the settlement period. It also doesn’t technically count as unavailable, and this has caused issues following the launch of bulk dispatch.
In the example below, a battery delivering a 5 MW frequency response contract uses a high-priced offer to reserve 5 MW of capacity. At the end of the EFA block, this offer is adjusted to reserve 25 MW for a new frequency response contract. This coincides with the battery delivering a PN of 20 MW with a ramp.
Bid/Offer levels are not fixed and are instead relative to the PN. This results in a brief period where the high-priced offer encroaches on available capacity. As a result, the unit cannot be dispatched for an Offer that it would have been otherwise.
Using MEL/MIL to declare unavailable results in better outcomes for both ESO and battery
Instead, the MEL should be used to reserve capacity for frequency response services. In this example, the MEL of the unit is set at 40 MW. This is because the battery only has 40 MW available for 15 minutes of dispatch. This means 5 MW is still reserved for frequency response.
Once the EFA block changes, the operator changes its MEL to 25 MW, reserving this for its new frequency response contract. As MEL is not proportional to PN, the battery is now available to receive the Offer to start ramping early. This means it can be dispatched and not miss out on revenue.
The move to the Open Balancing Platform should help with data issues
The Open Balancing Platform has been designed to handle large quantities of data. However, the original legacy systems have not. The ESO said they will continue using legacy systems until the OPB is fully developed (expected in 2027). This means they must continually monitor how their systems handle the data.