By PAUL YOUNGER
Scotland has become the first part of the UK to stop burning coal to supply
electricity following the closure of Longannet, its largest power station,
on March 24.
It is a sign of the times, with the rest of the UK’s coal-fired power
stations on death row after energy secretary Amber Rudd announced late last
year that they will all be forced to close by 2025.
For many reasons, it is hard to mourn the demise of coal-fired power.
Around 12,000 miners are killed around the world each year, most of them
digging for coal; abandoned mines cause widespread water pollution; and
coal-fired plants pollute the air with the likes of nitrogen and sulphur
compounds, as well as the highest greenhouse-gas emissions of any major
source of energy generation.
In the absence of carbon capture and storage, a technology which would be
ready more quickly if the government backed it properly, plant closure may
therefore seem sensible – even while we should help those that lose their
jobs and regret the loss of skills from the workforce.
That would be all there was to say were it not for a few harsh realities of
electricity supply. There are two reasons why coal-fired power plants have
survived so long.
Coal is cheap; only since the US shale-gas boom has it been consistently
beaten on price. And coal-fired plants are particularly suited to providing
power on demand at short notice, as well as providing crucial stabilisation
services for frequency and voltage across the grid.
Power on demand
If we are unable to dispatch electricity on demand, we must expect blackouts.
To do away with coal-fired power before alternatives are available is bold,
to say the least.
Gas-fired plants can play the same role, of course, but we have not been
building them in the UK in recent decades. And the economics for doing so
have been made very difficult by the capacity-auctions system that helps to
fund them, which has also seen many existing plants mothballed.
As for nuclear power, it is low-carbon but provides electricity at a
constant rate and therefore can’t be increased to track demand. Besides,
the ongoing fiasco over Hinkley C – and by extension nuclear new-build in
general – hardly makes it look a great contributor to energy security in
the foreseeable future.
Among the renewable sources, the only one that offers equivalent
dispatchable power is biomass combustion – burning mainly wood – but it
also entails air-quality challenges and its sustainability is debatable.
Hydropower is seasonally limited, while wind and solar are incapable of
dispatchable output.
The consequences are not just for the future, either: to compensate for the
reduced coal-fired and gas-fired power, National Grid has been quietly
allowing energy companies to set up “diesel farms” of temporary generators
in England to provide extra power in peak, even though it’s more damaging
than coal.
But can’t we just store renewable energy, whenever it is generated, and
dispatch it at times of high demand? Let’s be clear: we have the technology
– it’s the affordability and scale that are challenging. Of the myriad
potential storage technologies, none are as yet close to being able to
store electricity at comparable scale and cost to our only grid-level
storage technology: pumped-storage hydropower.
But pumped storage can only do so much. Let’s assume the UK could muster
sufficient wind power to meet one third of our typical daily electricity
consumption (40 GW to 45 GW).
In the absence of dispatchable power on demand, to offset the kind of
three-day calm period that is common during spells of high pressure in
winter, we would need to be able to store around 1,000 gigawatt hours (GWh)
of power. Yet pumped storage hydropower in the UK only totals 30 GWh, from
four stations.
If we are going to manage without Longannet and all the other gas-fired and
coal-fired power stations, we would need at least 970 GWh of storage – more
than a hundred pumped hydropower stations of comparable size to those we
already have.
This would be unlikely to cost less than £100 billion. And do we even have
100 plus upland catchments we’d be happy to impound and manage for this
purpose? Even if most of the UK uplands were not (rightly) zealously
protected conservation areas, it seems implausible that the UK could find
sufficient sites.
Add the important caveat that you lose energy sending it back and forth to
a storage facility, between 10% and 35% depending on the technology. This
means that relying on renewables and increased storage means you would need
substantially more total generating capacity than at present.
The voltage issue
So far we have only talked about power quantity, whereas power quality is
also crucial. To keep voltage within prescribed bounds requires “reactive”
(or “wattless”) power. Coal-fired power-stations have long been the
mainstay of this activity – not least in Scotland.
It has to be done regionally, so you can’t make up for this with coal power
from elsewhere. Wind turbines cannot provide reactive power control. Since
nuclear is being phased out in Scotland, gas-fired power is again the only
alternative.
So as we close plants such as Longannet, we can expect serious problems
with voltage control. This bodes ill for the electrical appliances and
devices on which we all increasingly rely.
With the closure of Longannet, Scotland thus becomes the first area of the
UK to take a serious gamble with reactive power. It will take not just good
management but a serious amount of good luck for the fossil-fuel funeral
wake not to be spoiled by flickering or failure of the lights.
In short, we may be heading into dangerous territory. The UK needs to get a
strategy together for building new gas-fired or coal-fired power, fitted
with carbon capture and storage technology, before the situation
deteriorates any further.
PAUL YOUNGER is Professor of Energy Engineering at Glasgow University.
Copyright © 2010–2015, The Conversation Trust (UK)
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