Energy regulator Ofgem has approved a change to the grid code that it says will allow better use of electricity storage in the balancing mechanism (BM).
Grid code amendment GC0166 introduces new parameters for limited duration assets (particularly what the BM calls electricity storage modules – ESMs), which address limitations in the National Energy System Operator’s (NESO’s) approach to using storage in managing electricity supply and demand.
Ofgem said NESO has circumvented the fact that the current framework does not adequately support ESMs by using maximum import/export limits and the ’30-minute rule’ to manage storage resources.
This differs from the intended use of maximum export limits (MEL) and maximum import limits (MIL), which should reflect the maximum possible active power of each module. Instead, ESM operators submit MEL and MIL based on the maximum power that can be delivered during a 30-minute period. When an asset’s charge status changes, operators must re-enter their MEL/MIL values.
However, Ofgem said this method means the control room has poor visibility into ESM availability for periods longer than 30 minutes, meaning it cannot easily use ESMs in the 24-hour schedule. This leads to ‘skips’, where NESO uses more expensive, usually fossil-fuelled, options to balance the system.
GC0166 introduces three new parameters:
-
Maximum Delivery Offer (MDO) that allows ESMs to indicate their actual export capabilities;
-
Maximum Delivery Bid (MDB), which allows ESMs to indicate their actual import capabilities;
-
And Future State of Energy (FSoE), which gives NESO a better insight into the availability of ESM over a longer time horizon.
The implementation of the change in the grid code will be technology neutral, so all balancing mechanism units (BMUs) will submit the new parameters, with BMUs able to re-declare MDO and MDB during specific circumstances, such as technical failures.
BMUs that can deliver for the full 90 minute BM period can declare defaults.
Ofgem said the proposal avoids “other potential distortions of discrimination” because it is technology neutral.
Justifying its approval of the code change, Ofgem said 11 of 14 respondents to the regulator’s consultation agreed that the proposal better facilitates the objectives of the network code, and six of seven respondents preferred the proposal to the baseline.
Batteries in the balancing mechanism
In 2024, several important changes were made to the BM. First, National Grid ESO (the grid operator that preceded NESO) was launched bulk shipping for battery energy storage units in the BM, allowing more battery instructions to be issued simultaneously.
It was also the year that the The 30-minute rule was put into useas an evolution of the ’15-minute rule’ that had previously been implemented.
This has been the case since the launch of NESO dedicated to improving battery skip rates (one of the consequences of the 30-minute rule) after receiving a letter from energy storage operators criticizing its methodology.
One of those commitments was to continue work on a number of changes to the code, to review and clarify the ’30-minute rule’ and to review the balancing reserve and wider reserves procurement strategies.
