06 Aug 2023
Wendel Hortop

Balancing Mechanism: batteries can only dispatch for up to 15 minutes

At the moment, there’s a big limitation on battery energy storage use in the Balancing Mechanism. Dispatches are essentially restricted to just 15 minutes in length. So, what does battery dispatch actually look like?

Wendel explains why batteries can only dispatch for up to 15 minutes in the Balancing Mechanism.

Are you a Modo Plus or Enterprise user? Once you’ve read this piece, head to our latest Deep Dive - to explore the dispatch lengths of different technologies and individual battery assets.

Batteries are overwhelmingly used for short-duration dispatches in the Balancing Mechanism

Batteries are almost exclusively used to deliver dispatches of 15 minutes or less.

  • The average length of dispatch for battery energy storage is 8.3 minutes - with no significant difference in length between Bids and Offers.
  • The majority of dispatches are for multiples of 5 minutes (either 5, 10, or 15 minutes in length). This reflects how the Control Room balances energy within each settlement period - essentially, it prefers to rectify issues at 5-minute intervals, where possible.
  • Outside of the 10- and 15-minute dispatches, most are 8 minutes or less. These actions are likely taken to manage frequency.

98% of battery energy storage Balancing Mechanism dispatches are 15 minutes or less. There are a handful of longer-duration dispatches, but these are anomalies (and, in theory, shouldn’t really happen). Realistically, batteries can’t be dispatched for longer than 15 minutes - but why?

Battery dispatch length is limited by the availability of state-of-charge data

At the moment, every battery Balancing Mechanism Unit (BMU) tells the Control Room how much power it can import or export for 15 minutes (via Maximum Import and Export Limits - MILs and MELs). Therefore, the Control Room knows that the battery can dispatch this duration (up to 15 minutes) - and it knows that the system can deliver.

Any longer, and the Control Room has no visibility of whether the battery has the energy to deliver - so it doesn’t send longer dispatches.

Work is ongoing to improve the visibility of energy for batteries - through groups such as the storage stakeholder working group. One suggestion is the introduction of a more adjustable ‘Maximum Delivery Offer/Bid’ parameter for battery energy storage.

Once a battery accepts a dispatch, it should update its MEL and MIL - to show what its state of charge will be at the end of the dispatch. This way, the Control Room knows how much extra energy is available, and can extend the dispatch if needed.

But are these dispatch extensions actually being used for batteries?

Extensions allow batteries to receive longer dispatches - but they aren’t used

Once we include extensions, the average battery dispatch increases to 8.8 minutes. Only 3% of battery dispatches receive extensions. The vast majority of BM actions for battery storage, therefore, remain 15 minutes and under. In short, extensions are not used to get longer dispatches from batteries - which is why the distribution of battery dispatches after extensions looks almost identical to the distribution before extensions.

  • Dispatches of 8 minutes or less get the most extensions.
  • Extensions of longer-duration dispatches are much rarer.
  • Even with extensions, the proportion of total battery dispatches over 15 minutes increases to just 3.2%.

Why aren’t extensions used more? They’re probably too convoluted...

To dispatch a battery for 30 minutes, the Control Room currently has to:

  1. Send an initial 15-minute dispatch to the battery.
  2. Wait for this dispatch to be accepted - and for a new MEL and MIL to be communicated back from the battery.
  3. If the battery has enough energy, send another 15-minute dispatch.
  4. And, if the battery doesn’t have enough energy, the Control Room needs to source this elsewhere.

Ultimately, attempting to use batteries for dispatches of longer than 15 minutes takes time and effort. The Control Room can otherwise send a single dispatch to an asset it knows can deliver for the required duration.

This limitation has a big impact on the Balancing Mechanism volume batteries can compete for

This limitation on dispatch length is a large part of the reason that battery energy storage gets skipped so much in the Balancing Mechanism. Currently, batteries can only really compete for around 24% of Balancing Mechanism volume.

If batteries could provide 30-minute dispatches, they would be able to compete for 69% of Balancing Mechanism volume.

Modo Plus and Enterprise users can head to our latest Deep Dive - to explore the dispatch lengths of different technologies and individual battery assets.