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expert reaction to Ofgem report on the power outage of 9 August 2019

Ofgem has published their report and recommendations on the UK power outage in August 2019.


Prof Keith Bell, Professor of Smart Grids, University of Strathclyde, and a co-Director of the UK Energy Research Centre, said:

What has Ofgem said about the August 9th incident?

“The Electricity regulator, Ofgem, has published its report on the electricity system incident that happened on August 9th.  It states that payments have been made into Ofgem’s “voluntary redress” fund by three major industry actors in recognition of direct impacts on electricity users or an impact that could easily have arisen in view of departure from correct procedures.  These actors are two generating companies – Ørsted and RWE – whose plant disconnected from the system when it shouldn’t have, and a Distribution Network Operator (DNO) – UK Power Networks – that started to restore demand before receiving confirmation from the Electricity System Operator (ESO) that it was safe to do so.

“Ofgem’s report confirms the broad sequence of events outlined in the Electricity System Operator’s (ESO’s) report from September1.  However, it states that investigations into the ESO’s performance are still ongoing.

What causes major electricity supply interruptions?

“Disconnections of electricity demand are not unknown.  On average, an electricity customer in Britain experiences one interruption per year.  Almost all interruption incidents are very localised and are the result of faults on the distribution network.

“Generally, speaking, the causes of electricity supply interruptions where a large amount of load is lost fall into one of two categories, or both of them:

  1. Due to extreme weather, such as affected the distribution network around Lancaster in December 2015;
  2. Due to an unfortunate combination of events within a short space of time.

“Although there was a lightning storm going on at the time, the weather was not extreme on August 9th and the incident that affected Britain fell into the second category.  None of the contributing events on their own should normally have caused any interruptions to electricity users’ supply.

What happened on August 9th?

“The initiating event was a short circuit on a 400 kV overhead line caused by a lightning strike.  Such faults typically happen tens of times each year on the transmission network and do not cause losses of supply.  On this occasion, however, it caused a steam turbine at Little Barford combined cycle gas turbine power station, owned by RWE, to trip.  It is still not completely clear why this happened or why, to compound the problem, a gas turbine there also tripped a minute later.

“The voltage depression caused by the short circuit fault also led to the loss of almost all of the power being produced at Hornsea offshore wind farm.  This, again, should not have happened.

“The network fault and the loss of generation at Hornsea and Little Barford caused the loss of further generation, small scale ‘distributed generation’ connected to the distribution network.  The combination led to a period in which there was not enough generation to meet demand and the system’s frequency started to fall.  ‘Frequency containment reserve’ scheduled by the ESO, mostly from generators but also from batteries, was not enough to prevent the system’s frequency from falling so far below statutory limits that automatic ‘low frequency demand disconnection’ (LFDD) equipment was triggered.  This disconnected an estimated 1.1 million electricity users.  According to Ofgem, those disconnected included supplies to Newcastle airport, two hospitals, some railway signalling and some water treatment works.

No cause for complacency

“By international standards, electricity supply in Britain is very reliable and the event on August 9th was small, largely because LFDD succeeded in preventing the situation from getting a lot worse.  However, the impact on rail users in the south-east, in particular, was significant.  This was largely due, so it seems, to the inadvertent operation of protection equipment on certain types of trains operated by Govia Thameslink.  Some water supplies were also affected.

“It is clear from the ESO’s report in September, Ofgem’s new report and conditions on the system at the time that the variability of renewables was not the cause of the event.  Also, one event cannot be taken as a sign of deteriorating system stability.  However, there is no cause for complacency.  Britain’s supplies of energy need to be progressively decarbonised and the technical characteristics of the electricity system continue to change.  The costs of the transition need to be kept to a minimum but electricity users will no doubt expect their future supply to be, on average, as reliable as it has been up to now.

Who is responsible for getting the engineering right?

“Ofgem’s report questions whether the ESO and the DNOs take sufficient responsibility in ensuring that equipment connected to the system – generators, interconnectors and loads – behaves in a way that contributes to system stability rather than putting the system at unreasonable risk.  This is arguably becoming more difficult than in the past.  The volume of small scale ‘distributed’ generation capacity has grown from an estimated 7 GW in 2009 to more than 37 GW today.  This represents tens of thousands of individual installations in contrast to the hundreds of power stations that met demand for electricity up to recent years.  (The annual peak demand for electricity in Britain is expected to be around 60 GW over the Winter of 2019/20).

“Ofgem that has said that either agreement was reached with licensed parties so that there was no need to make a determination on licence compliance, or that it was satisfied that licences were complied with.  However, it has stated that investigation into the ESO will continue.  Also, in my view, Ofgem’s report highlights areas where engineering practice could and, arguably, should have been better.  However, whether the fundamental basis on which the ESO procures frequency containment reserve should be changed is an open question.

What needs to be done now?

“The electricity system needs to be decarbonised; the engineering also needs to be got right.  As the 2019 UKERC Energy Policy Review2 argued, in my opinion the August 9th incident shows that responsibilities for ensuring electricity system resilience – preventing, containing and recovering from interruptions to supply arising from disturbances – need to be clarified and applied in a more rigorous way.  This includes monitoring and controlling DG and improving the network licensees’ ability to understand and manage the system’s new behaviours.  Issues that have been known about within the sector need to be addressed, in my view, with greater urgency.

“With the need for new skills and insights, it’s unfortunate that, last year, the UK Government’s main research funding agency decided to cut funding from its core ‘Centre for Doctoral Training’ programme to PhD students working on electricity system issues.”




Duncan Botting, Chair of the IET’s Energy Sector Executive and member of the IET’s Energy Policy Panel, said:

“What the incident on 9 August highlighted is that we have a highly complex system which the National Grid is only one part of.  This is interconnected physically and through data and information, flows to many other systems – such as the Network Rail system and subsystems within it.  The role that all stakeholders play in this complex system of systems, including government, regulators and the new Internet of Things (sensors and control systems below the regulated businesses), as well as the inter-connected governance systems that these connect with, highlights the need for lessons to be learnt.

“As the UK moves to reduce emissions to net-zero, even greater change is coming, and it is essential that we can maintain an energy system that is secure and resilient.

“The report, we feel does not make enough of this complexity, and does not highlight enough the risk that the current silo-based approaches to governance, commercial and technical solutions that are based in an analogue era will have, as society’s dependence on electricity continues to increase and environmental, technology and social norms continue to exponentially transform the challenges for that system.

“The technical governance of these complex systems requires a step change from today, it needs to be holistic, agile, flexible and embracing of the full range of system participants.  Without that we can expect to see more unexpected consequences across the whole system, as well as a failure to seize the benefits whole systems cooperation can bring, not just for major events on the National Grid, but also for the much more numerous power cuts experienced locally every day.

“The IET and Energy Systems Catapult conducted a six year review of Future Power Systems governance and technical challenges.  For more information, please visit”


Prof Chris Sansom, Professor and Head of the Centre of Renewable Energy Systems, Cranfield University, said:

“The OFGEM report on the UK power cuts of August 9th last year underlines the urgent need to address the issue of dispatchability in a low-carbon power generation nation.

“The cuts were caused initially when a lightning strike took out the “Hornsea One” offshore wind farm and the Little Barford gas power station, together with a number of distributed units.

“In a low-carbon world, the intermittent nature of renewable energy sources will be an additional factor in reducing the predictability of electrical supply.

“Current thinking seems to revolve around electrical storage to address the problem, whether it be utility-scale or distributed small-scale (battery) storage.

“But there is a much simpler and cheaper solution, namely that of large-scale thermal storage.  It is difficult and expensive to store 500MWh of electrical power, but a factor of ten times cheaper to store the equivalent amount of heat.  In fact, the solution is already out there.  In the large CSP (Concentrating Solar Power) plants of southern Europe, North Africa, and the USA, there are large thermal stores (over 100MWh) which form an integral part of the power plant, using molten salts at temperatures up to 600C as the energy storage medium.  Powered by the sun, the plants can operate at night too.

“The same technology could be utilised in the UK.  Surplus electricity from renewable (and other) energy sources could be converted into heat and stored in large molten salt storage tanks in the soon-to-be defunct fossil fuel thermal power plants.  They would be the ideal location, since they already possess the electrical generators to transform the heat back to electrical power on demand, and the grid connectivity.  On both cost and dispatchability, it could beat pumped hydro and large-scale battery storage.”


Prof Tim Green FREng, Co-director of the Energy Futures Laboratory, Imperial College London, said:

“The report released by Ofgem this morning covers three areas:

  1. Who performed properly and who did not during the power cut of 9th August
  2. What immediate steps should be taken to avoid repeat of same issue
  3. What do the circumstances of the power cut tell us about things on the horizon as we use more renewables and head to net-zero.

“A lot of the initial response to the report has focused on the “fines” (actually, payments they have agreed to make) to be paid by RWE and Ørsted as operators of the two large power stations that failed on the day.  Both companies have accepted that their power stations did not “ride-through” the lightning strike event in the way that they should have (according to the Grid Code) and both have taken actions to ensure that the same thing will not happen again.  National Grid Electricity System Operator (NG ESO) was not required to make a payment because it was not found to have breached any of its licence terms but there are many recommendations directed at it.  The identification of parties who were at fault is actually a small part of the report and much more of the report draws out broader lessons to be learned.

“NG ESO is told it should be more transparent about how it calculates how much reserve power to hold, especially over how it accounts for the likelihood that some small distributed generators may self-disconnect during a major disturbance.  There is already a programme to reduce the likelihood by changing the protection arraignments for small generators and this was accelerated during late 2019.

“There is also to be a swift review of an important standard, the Security and Quality of Supply Standard, that defines the sort of credible disturbances for which NG ESO must prepare.  At present NG ESO must hold reserve to cover for the sudden failure of one large power station but not two in quick succession.  This review will consider the benefits and costs of securing against a wider range of events.  Doing so would give the UK an even more robust grid system but would require NG ESO to buy more reserve services from generators and batteries and therefore costs and prices would rise.  National Grid spend about £130 M per year on purchasing such services – increasing this to cover for the loss of two large power stations at the same time would add in the region of £10 per year to the average household bill.

“NG ESO is also being told to improve the way it ensures that generators comply with the Grid Code, and the operators of local networks (the Distribution Network Operators, DNOs) are being told to improve their preparation for Low-Frequency Demand Disconnection (LFDD).  LFDD is the emergency action taken on 9th August that kept the bulk of the gird running but disconnected over 1 million consumers.  It worked largely as expected but DNOs are being told to improve their understanding of what essential services may be included in any disconnection, create a better-chosen and more assured set of disconnections and to brief customers on the implications of such LFDD actions for their businesses and services.

“There is also a strong flavour in the report that simply fixing the immediate problems exposed by the power cut is not enough.  The UK has halved its carbon emission from electricity in the last decade, with many accompanying changes in grid operation, but the challenge now is to reach net-zero emissions.  One of the themes of the report is that the risks of malfunction of the grid are changing as we increase renewable generation and stand-down fossil-fuelled generators.  That is well-known and widely-discussed in the industry but here we have the regulator stating that standards, practices, visibility and data availability need to be kept in constant review so that as we decarbonise, we do not jeopardise the reliability of the grid.  There are some large challenges ahead, and this report focuses attention on them, and present and future generations of engineers have some important and stimulating work to do.”


Prof Jon Gibbins, Director of the UK Carbon Capture and Storage Research Centre, and Professor of Carbon Capture and Storage, University of Sheffield, said:

“The report indicates a complex combination of causes for the power cuts, some of which are not explained in detail and do not appear to be fully recorded or understood.  So some of the underlying problems noted in the report can be addressed, but not all.  The report says relatively little about what can be done to avoid blackouts, irrespective of their causes, which is to ensure there are reliable ways of very rapidly suppling large amounts of extra power to the grid.  In a net zero (and eventually net negative) electricity system, gas and biomass power plants with carbon capture and storage are uniquely able to provide a big boost to the system when required (see – provided this capability is recognised and valued now, as government and industry develop long term investment plans for the electricity sector.”


Declared interests

Prof Keith Bell: “Keith Bell is a Professor of Smart Grids at the University of Strathclyde and a co-Director of the UK Energy Research Centre.  Information on his work and publications can be found at  As can be seen from his web page, in the past he has done work with Ofgem, BEIS, some generation companies and a number of the network licensees, including National Grid.  As will be expected, he aims to speak independently and objectively, based on evidence.”

Duncan Botting: No conflicts that are material to this response, but for clarity he sits on the BEIS/Ofgem Smart Systems Forum on behalf of the IET.

Prof Chris Sansom: “I don’t have any interests to declare.”

Prof Tim Green: “Tim Green is the co-director of Energy Future Lab, Imperial’s cross-disciplinary energy institute with responsibility for facilitating interdisciplinary research and postgraduate education in energy and in coordinating its dissemination.  He is also Deputy Head of the Department of Electrical and Electronic Engineering.  His personal research focuses on the analysis and technology to support the development of a low carbon electricity supply network that is able to accommodate variable renewable sources and new widespread electric vehicle charging while still delivering a cost effective and very reliable service. His research specialisation is in power electronics for use in power systems.”

Prof Jon Gibbins: “Director of the UK CCS Research Centre and involved with the development of CCS clusters in the UK.”

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