By David Watson
There’s more to claims of ‘record-breaking’ periods of coal-free
electricity generation in the UK than meets the eye.
British electricity consumers may have noticed an announcement by the
National Grid Electricity System Operator (ESO) on 28 April that the
‘record’ of more than 18 days without any coal being burned to generate
electricity in the United Kingdom, which had stood since the Victorian era,
had been broken. ESO director Fintan Slye’s claim at that time of “…the
longest period of coal-free operation in Britain” was widely reported,
including in E&T. ESO was back on 2 June stating that this “incredible
coal-free run” now stood at 53 days and counting.
While this may imply a tautological truth that renewables are inexorably,
seamlessly and dependably replacing fossil-fuel-based electricity supplies
within the UK Grid, that’s not the case.
Prior to the ‘record-breaking’ period, coal’s contribution to UK power
generation stood at only around 2 per cent. Coupled with that, the UK had
experienced a very mild and calm seven-day period commencing on Thursday 23
April, which along with Covid-19 reduced UK electricity demand to around 18
per cent less than the seasonal average. At the same time, wind generation
had virtually collapsed across the UK, and was to collapse totally on 3, 6,
7 and 8 May.
In spite of this reduced demand, throughout that week and in early May the
country was dependent on imported power to keep the lights on and hospitals
running. Three interconnectors to mainland Europe were supplying up to
their maximum capability of 4,000MW – equivalent to more than three Torness
In a random check I made in April, Scotland was importing more than
1,200MW, equivalent to a second Torness, to keep the becalmed country
functioning as the Covid-19 spread was accelerating.
There was no mention from the ESO that the UK ran rarely used old
open-cycle gas turbines (OCGTs) on 23 April, presumably to meet demand.
While this avoided using coal, OCGTs are much less efficient, much more
expensive to operate and with the waste gases directly exhausted release
much more heat energy and carbon dioxide to the environment than the
combined-cycle gas turbines (CCGTs) they were supplementing. OCGTs are
normally only used rarely, if at all, and then in winter when both demand
and electricity prices are much higher. Otherwise they are uneconomic.
Through this ‘record’ period the UK has imported 10 per cent of its
electricity from Europe. Much of this is coal-generated, so during this
‘record setting’ UK electrical power was not ‘coal free’. Neither were gas,
nuclear, solar and wind able to keep the lights on by themselves.
Around 15 per cent of electricity generated in the Netherlands is from
coal. The proportion in Germany is around 30-38 per cent, which will
increase when Datteln 4 is commissioned this year, using ‘hard’ coal with
the highest concentration of carbon. Germany is also a major exporter to
both the Netherlands and France, so French exports to the UK routinely
include both nuclear and coal-generated power. At midday on 30 May, for
example, Germany was exporting 3.6GW to France, which was in turn exporting
924MW to the UK.
In the run up to Brexit, the UK has been working towards establishing a
further six or seven interconnectors to mainland Europe which will lead to
it increasingly offshoring carbon-dioxide emissions as it works towards
achieving net zero. Carbon data for imported electricity is not counted in
UK statistics and this approach is increasingly being referred to in the
profession as the ‘least cost pathway to de-carbonisation’.
UK generators pay a carbon tax on emissions from domestic generation, but
not on imports, so the economics of investing in new gas generation are
distorted. Creating new gas-generation capacity in the UK would, of course,
be much cleaner than importing a similar level of coal-generated power –
gas accounts for roughly half the pollution even without carbon capture and
storage. This is comparable to loudly and self-righteously surrendering
fossil-fuel cars in support of net zero while quietly continuing to use our
neighbour’s vehicle whenever it’s convenient.
On 6 May Ofgem revised its ‘cap and floor’ regime to facilitate the
softening of financial rules for the planned Greenlink and NeuConnect
interconnector projects, to try and ensure they proceed, while cautioning
that: “Interconnectors can import from low-carbon markets, reducing system
emissions; however, they could also import electricity from markets with
higher emissions (which would be negative for decarbonisation).” Which
implies the regulator is less than convinced by the “least cost pathway to
In the mix too, of course, is the EU fast-track Projects of Common Interest
planning system, designed to encourage interconnectors across Europe and
provide some funding via the Connecting Europe Facility, which presently
includes almost all of those planned between the UK and mainland Europe. If
this is lost post-Brexit, then a cooling of the private investment that CEF
stimulates will cause a problem for the ESO and its current policy of
It’s also probable that in the wake of Brexit the UK will have to
relinquish its seat at the Agency for the Cooperation of Energy Regulators
and drop to a technical issues input role within the European Network of
Transmission System Operators. Operational responsibilities for the
interconnectors will remain though, which means the UK will have to comply
with existing and future EU regulations on energy, competition and state
aid that it will be largely unable to influence.
So, what future for the UK?
There was never enough modelling and forethought put into Grid development
before the rush to unpredictable, non-despatchable and now embedded
distributed renewables and generation. The country is having to play catch up.
The major Grid failure on 9 August last year illustrates this. Following a
lightning strike that triggered the failure of Hornsea windfarm and Little
Barford CCGT power station, frequency control was lost, supplies to 1.15
million customers failed or were ‘load shed’ (disconnected), and around 30
trains tripped on low frequency and most had to be manually reset, taking
hours and causing disruption to around 590 services. Neither Hornsea nor
Barford could meet their Grid Code ‘ride through’ obligations and the ESO
had insufficient reserve available.
Ofgem completed its initial research into the incident in January 2020 and
tabled 50 pages of technical concerns of national importance across the
roles and engineering of the ESO, the generating companies and two
distribution companies involved in what amounts to a relentless and precise
identification of myriad technical and procedural failings across the
participants. There is hardly a key technical aspect of the event about
which it is not critical.
A report that is a scarcely believable and close to frightening for any
power systems engineer cites a number of significant ‘lessons learned’:
“The outage highlights the risks and challenges of managing system security
and stability in the evolving electricity system as well as the importance
of robust industry processes.”
“The ESO should have been more proactive in understanding and addressing
issues with distributed generation and its impact on system security.”
“Where the ESO is connecting complex power systems to the network, it must
be capable of modelling their performance when the network is disturbed. In
addition, the process for understanding and ensuring the issues behind
fault-related outages prior to reconnecting generators should be made more
“Further improvements to the ESO structure and governance framework should
be considered in order to meet the challenges of the energy transition.”
“The ESO should consider and come forward with recommendations to
improve… its holding of reserve, response and system inertia…” [This
includes balancing services.]
Given its serious concerns, Ofgem said it would review the roles of the
System Operators during the course of this year.
Renewables penetration has reached the stage where the ESO is now publicly
advising that the Grid needs more inertia and reactive-power capability to
support frequency and voltage stability as a result. Closure of large
synchronous stations will worsen the situation. All of the UK’s hugely
stabilising nuclear stations, bar Sizewell, will be closed within the next
few years. Many of us in the profession have been predicting this for many
years and the ESO similarly would have been aware throughout. The ESO’s
declared approach is to now call for this to be actioned and inertia and
reactive power to be purchased by grid users. This is a direct consequence
of increasing renewables and will add hugely to the real cost of renewables
and to users’ bills.
First, however, this capability has to be engineered and made available.
Scottish Power, including via its ‘Migrate’ stakeholder engagement event on
29 October 2019, has been talking of central Scotland likely requiring up
to seven 300MVA synchronous compensators with large flywheels to protect
its area of the Grid. These would also provide a much-needed system-fault
infeed of 7,000MVA to protect system protection, addressing the stability
lost when Longannet closed.
I know of no other country in the world contemplating this scale of
deployment, and it is still at the prototype research stage. Who knows what
this will cost across the UK and how long it will take?
Lack of large-scale UK synchronous generation is also exposing the country
to an increasing ‘black start’ problem, which is a growing crisis. Wind and
solar renewables cannot restart us and additional VSC interconnectors to
Europe aren’t yet built.
The UK now has a privatised and fragmented industry, mostly owned by
foreign businesses, which apparently lacks the legal obligations to agree
and implement a long-term coordinated strategy that best suits users while
we remain fully dependent on European imports to keep the lights on.
Like herding cats, Ofgem or preferably a new centralised fully empowered
energy authority needs to address how this disparate assembly of private
companies can be focused to help formulate and follow a coherent grid
stability and net-zero strategy. We cannot continue to rely on markets
rather than planning and designing the UK’s future grid. For a sovereign
country to arrive at this situation is incredible.
Meanwhile, is seeking “records” seriously tackling emissions? No. Have wind
renewables failed us during an unprecedented health crisis? Yes.
Being able to claim a record-breaking ‘coal-free’ period ahead of the next
government white paper on energy will look good in front of the
politicians. Ofgem has advised ESO of far more important issues requiring
its urgent attention.
David Watson is a chartered electrical engineer who before retirement was
manager of projects at Foster Wheeler Energy, based in Glasgow and
responsible for project-execution management at the company’s Scottish