The Role of Distributed Generation in the UK Blackout of 9 August 2019

It has been widely claimed that Distributed (or embedded) Generation, such as solar and wind connected to the low voltage distribution network, reinforces electricity system stability.

The final reports into the widespread blackout of the 9th of August last year by the UK electricity regulator, Ofgem, and the British government’s Energy Emergency Executive Committee, E3C show that this is not the case. Distributed Generation is now under the spotlight as a leading cause of the severity of the 9 August blackout, and as a hazard increasing future risks to security of supply.

Both the UK electricity market regulator, Ofgem, and the Energy Emergencies Executive Committee (E3C) of the Department for Business, Energy and Industrial Strategy (BEIS) have now (3 January) released their final reports into the blackout on the 9th of August 2019, a blackout that disconnected over 1 million consumers for nearly an hour with knock-on impacts that persisted for days in many cases and in case, an oil refinery, for several weeks:

Ofgem, Investigation into 9 August 2019 power outage

E3C, Great Britain power system disruption review

The two studies have different roles. Ofgem’s work, which is now almost complete (there is just one more as yet unpublished technical paper, see p. 10) concentrates on regulatory compliance, that is to say on whether the relevant parties, National Grid, the Distribution Network Operators, and the generators, breached the terms and conditions of their various licenses. In essence it is a retrospective, forensic and essentially historical study.

The E3C work is more forward looking and aims to examine measures that should or are being taken to a) reduce the likelihood of a recurrence of a similar blackout, and b) improve the way in such a blackout is handled in the event that it cannot be prevented.

The two studies are as far as I can tell entirely consistent, but they are complementary; and they need to be studied together.

Those who have been following the blackout story from the outset, as well as more casual readers of press stories on the blackout, some of which I have discussed in a previous post (“Telling the Story of a Blackout”), will want to know what new facts and analytic interpretation of the blackout emerge from these two studies.

The answer is that there is a good deal here, but it is not initially obvious, and at first glance such readers may be disappointed. While there are some new or at least newish facts these are mainly confined to details, and often about the consequences of the blackout rather than its causes. For example we learn that some four hospitals, not just the much-reported case of Ipswich Hospital, were disconnected during the blackout (see Ofgem, p. 20; E3C p. 19), and that National Grid perhaps over-zealously reconnected the Hornsea 1 before it was confident that the wind farm’s “technical issues”, which had without doubt contributed to the blackout, had been fully understood. We also learn that 371 rail services were cancelled, and 220 part cancelled, with three Transport for London tube stations, and eight rural signalling stations all disconnected, though without significant effect on services (Ofgem, p. 20).

Many of these details are certainly important in themselves, and Ofgem even singles out for particular criticism National Grid’s hasty reconnection of Hornsea (Ofgem, p. 28), but the principal novelty and value of these two documents is not in such material minutiae pure and simple, but rather in the general and cumulatively damning description of weaknesses in the UK electricity system that emerges from this material when it is put into the context of the event overall. It is proverbial that electricity systems shift from stability to chaos in fractions of a second, while the causes of a blackout take weeks and months to understand, but the mists are beginning to clear and we are beginning to get to grips with what happened on the 9th of August.

However, with regard to the story of the blackout, the main narrative has not changed much since last year; a lightning strike trigged the disconnection of, firstly, 150 MW of Distributed Generation, closely followed by the almost instantaneous loss of 737 MW of the Hornsea 1 offshore wind farm. Shortly after that the steam unit at Little Barford Combined Cycle Gas Turbine tripped off. All of this occurred within 1 second of the lightning strike. The consequent drop in frequency triggered further disconnections of Distributed Generators. Additionally, the first of the two gas turbines at Little Barford also now had to disconnect, closely followed by the second of the two gas turbines, and yet more Distributed Generation. (See Ofgem pp. 16–19).

Even in this sketch of the summary it will be obvious to those familiar with earlier accounts that while the main facts remain, the light cast on them has changed significantly, and this results in a somewhat different picture. Attention has switched from the two main Transmission System connected generators, Hornsea 1 and the Little Barford, which have both been fined £4.5 million each for failing to ride through the fault, and is now focussed on Distributed Generation, that is to say on generators connected to, and sometimes said to be “embedded within”, the Distribution Network. These generators are usually invisible to the system operator and can range from very small domestic systems, right up to what are by any standard large onshore wind and solar installations.

The role of Distributed Generation in the blackout was, of course, known from quite early on in the post-event analysis, but the scale is only now becoming fully apparent, though even at this late stage it remains and will remain uncertain. The E3C report goes so far as to remark that “There is a significant possibility that the total volume of loss of embedded generation on 9 August is in excess of the transmission connected generation lost during the event.” Since the transmission-connected generation lost comprises Hornsea and Little Barford, and this totals 1,384 MW, we can infer that somewhere in the region of 1.5 GW of Distributed Generation disconnected in several closely proximate phases over the entire event. That is itself a significant quantity, and suggests that, as the E3C remarks (p. 9), the total generation loss during the blackout was a monumental 3 GW.

But it is not simply the quantity of Distributed Generation that disconnected which is striking. The manner in which it was lost is also important. Ofgem notes, paragraph 2.4.12 (p. 19) that when system frequency fell below 48.8Hz, the Distribution Network Operators (DNOs), disconnected approximately 5% of load, totalling 892 MW of net demand. However, following a hint in the original National Grid Technical Report, Ofgem comments:

The ESO reported that the net demand reduction seen by the transmission system was only 350 MW. This indicates that approximately 550 MW of additional distributed generation was lost at this point. The reasons for this need to be better understood and addressed to avoid it happening again.

The DNOs disconnected 892 MW of demand, but the observed benefit to the system at this time of extreme stress was only 350 MW.

The E3C study gives a little further clarity on this point, noting that “550 MW of embedded generation was disconnected, either as part of the LFDD scheme or via another unidentified mechanism” (E3C, p. 9). The Low Frequency Demand Disconnection (LFDD) scheme is the remedial measure taken during a blackout by the Distribution Network Operators to bring supply and demand back into balance. Thus, much and perhaps all of that 550 MW of embedded generation was disconnected by measures taken to address the blackout. Because of the presence of embedded generators the remedial action take to address a system disturbance actually made the problem worse, cutting the net benefit of the measure.

Ofgem is quite right to say that this problem should be better understood, but it is difficult to see how it can be prevented in the future, as they hope, except by preventing whenever possible the disconnection under LFDD of any area where there is any significant concentration of embedded generation. Of course, that assumes that the system operators are still able to choose which areas will be disconnected, but in a severe system disturbance they may not have that degree of control.

How has this problem with Distributed Generation crept up and surprised us in this way? Who is to blame? Few if any elements within the UK electricity supply industry come out well from the 9th August blackout. Both Hornsea and Little Barford have been penalised. But neither of them are embedded generators, and they have no role in the management of such generation. National Grid was not fined, and superficially emerges from these studies exonerated: Ofgem puts the point unambiguously:

We have not identified any failures by the ESO to meet its requirements which contributed to the outages.”

But this is obviously as much a comment on the licence terms as the performance of National Grid, and both Ofgem and E3C are sharply critical of several aspects of its conduct both before and after the blackout, including embedded generation, Ofgem even remarking that:

[…] the ESO could have been more proactive in understanding and addressing issues with distributed generation and its impact on system security. (p. 22)

The implication seems to be that while National Grid was not, legally, in breach of its licence as Electricity Systems Operator, Ofgem has concluded that it has been complacent in its attitude towards emerging and novel problems in the UK electricity system. Many commentators, including Colin Gibson and Capell Aris, former National Grid employees, have said as much over and over again (Former National Grid director says ministers should impose limits new wind and solar farms to help avoid power cuts). It will be interesting to see what comes of the E3C requirement that National Grid review the crucial Security and Quality of Supply Standard (SQSS) with the aim of understanding the “explicit impacts of distributed generation on the required level of security” (p. 15).) If the consumer interest is respected this could be very interesting.

Taken together these studies of the 9th August blackout report systemic fragility problems in the UK electricity supply industry, but not only within the production side of the industry. National Grid, the generators, the DNOs, none emerge smelling of roses, but the E3C also observes that the consumer sector itself is poorly prepared (p.18ff). As a matter of fact, they are encouraging consumers of all kinds to develop “strong business continuity plans” covering “a range of credible power disruption scenarios”. This is MBA Jargon, but is not too hard to put into everyday French: Sauve qui peut.

It seems probable that consumer side weakness is the outcome of a long period of robust electricity supply, under the CEGB and its inheritors, meaning that consumers never had to test, adapt or even go to the difficulty and expense of developing measures that ensure their lives and businesses are robust in the context of a fragile electricity system. They could rely on the system. That is not the case today.

The costs of a largely decentralised generation portfolio, much of it composed of low inertia generators such as wind and solar, are not limited to the technical athletics of the System Operator, but also involve the need for a forewarned and forearmed consumption market. Thanks to energy and climate policies, British consumers from households to hospitals must now ensure that they are able to handle not only the more extreme grid management measures required by a “smart”, “clean” system but also the consequences emerging when those measures prove inadequate. Taking up the slack, which is what “strong business continuity plans” ultimately means, will not be cost free.

Dr John Constable: GWPF Energy Editor