Keeping the lights on (in lockdown Britain) when the sun is shining

Will some smaller generators find themselves disconnected from the grid during the course of the UK’s upcoming VE Day anniversary bank holiday (8 May 2020)? We look here at an urgent modification to the Grid Code that is intended to facilitate such disconnections – as a measure of last resort.

For some time, it has been clear that on hot, sunny days in summer, balancing maximum output from solar installations and minimum demand for electricity presents a challenge for National Grid ESO (NG ESO) as GB system operator. NG ESO has developed, and continues to develop, a number of ancillary services tools to address this on a commercial basis, providing incentives for other forms of generation to turn down, or demand to turn up, for example.

However, recent falls in overall electricity demand arising from the UK’s current “lockdown” conditions have gone rather further than is usual. The lack of demand from commercial and industrial premises, where businesses are not operating as a result of COVID-19, has not been offset by additional residential sector demand from those who have been furloughed or are working from home. Particularly with the bank holiday looming, NG ESO envisages that it may have to take additional measures, including, as a last resort, disconnecting generators to maintain grid stability.

Where a generator is connected to the distribution, rather than the transmission network, NG ESO has no means of instructing it to disconnect or de-energise. Although in some cases NG ESO will be able to achieve an equivalent result, for example through the Balancing Mechanism, this is not the case with those “embedded generators” that do not have connection agreements with NG ESO and are not otherwise party to industry frameworks such as the Balancing and Settlement Code.

In such cases, the obvious way for NG ESO to achieve disconnection or de-energisation of an embedded generator is by instructing the operator of the distribution network to which it is connected to disconnect or de-energise it. Given the thousands of pages of industry codes to which NG ESO and the DNOs are parties, it might be expected that somewhere there would already be a provision that clearly enables NG ESO to disconnect or de-energise a generator as a measure of last resort in the kind of circumstances that may soon arise (even if the COVID-19 crisis itself is unprecedented).

Arguably, such a provision does exist, but it is expressed in very brief, vague and generic terms. If DNOs are going to be instructed to take such drastic action, it seems appropriate to have clearer and more focused wording. Accordingly, NG ESO put forward on 30 April 2020 an urgent modification to the Grid Code, for which it sought approval by 7 May 2020 (in time for the VE Day Bank Holiday). Ofgem’s decision, granting urgent status and dated 1 May 2020, was published on 5 May; the Grid Code Panel’s recommendation was published on 6 May and Ofgem’s decision approving the modification was published on 7 May 2020.

The main change is time-limited until 25 October 2020. It gives NG ESO the right to issue DNOs instructions requiring them to disconnect embedded generators. This “includes the disconnection of [embedded generators]…which are owned or operated by generators that are not BM Participants”. The instructions may: “i) be specific and require the [DNO] to disconnect specified [embedded generators]; ii) be for the [DNO] to disconnect [embedded generators] supplied via one or more specified Grid Supply Point(s) with an aggregate Registered Capacity of a specified value; or iii) be for the [DNO] to disconnect [embedded generators] supplied via one or more specified Grid Supply Point(s) such that a specified proportion of the aggregate Registered Capacity is disconnected”.

If NG ESO instructs DNOs to de-energise embedded generators, the Distribution Connection and Use of System Agreement would oblige the DNOs to re-energise them “as quickly as reasonably practicable after the circumstances leading to the De-energisation have ceased to exist”. There is no provision for compensation to be paid to generators for any revenue lost during the period of de-energisation (unlike many cases where emergency instructions operate as bid or offer acceptances in the balancing mechanism).

The modification proposal stressed that NG ESO would only exercise its new/clarified right as a last resort, and that it is only a stop-gap solution. As well as considering the development of further ancillary services, NG ESO indicated that in the longer term it intends to develop “a more considered solution…potentially by developing a roughly symmetrical arrangement to the existing demand control conditions contained in section OC6 of the Grid Code”. OC6 is the part of the Grid Code that enables NG ESO to respond to situations of “insufficient Active Power generation being available to meet Demand” on the transmission system by, for example, requiring DNOs to disconnect a certain proportion of demand within their areas on two minutes’ notice. OC6 covers some 10 pages, compared to the 10 or so lines of drafting in the modification.

Industry codes are not noted for their brevity of expression, but it seems likely that some more developed provisions on this point are desirable, even if it is to be hoped they never need to be used. For example, the modification introduces the concepts of disconnecting a certain proportion or amount of embedded generation associated with a particular Grid Supply Point, or a specified embedded generator. This mirrors the concept of rolling disconnection of tranches of demand in OC6, but there is more to be said, perhaps about the basis on which DNOs would exercise any discretion they have in determining how to carry out instructions from NG ESO that are not generator-specific. It may also be appropriate to refer to disconnection of embedded generation in a revised edition of the Balancing Principles Statement that NG ESO is required to produce under condition 16 of its licence. The fact that a proposal submitted at such short notice attracted comments from 69 interested parties in a few days, and the number of questions raised by the Panel in its report on the proposal, also suggest that we are some way from hearing the last word on this subject.

The authors are extremely grateful to Charles Wood for his assistance with this post.

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