By DB Watson
WITH fanfare, National Grid’s Energy System Operator (ESO) recently
announced plans to bolster frequency control in the north of Scotland by
providing a £25 million giant flywheel at Keith, the south end of the
Spittal (near Thurso) to Blackhillock (Moray) high voltage direct current
(HVDC) undersea interconnector.
Loss of frequency protecting rotational inertia as large generating plants
close, for example coal and nuclear, is not replenished as windfarm or
solar generation increases. The rate of frequency variation also
consequently speeds up further increasing network stability challenges.
Billions have and continue to be spent on high capacity HVDC transmission
to route wind generation to load. The recently commissioned Beatrice
offshore windfarm near Spittal with a Contract for Difference price of
£158/MW Hour escalable ( Hinckley Point C nuclear is circa £98) connects
into this new £1.1 billion system.
The chosen HVDC/AC (alternating current) interconnector (a “Voltage Source”
type) at Spittal was found, mid project, to have a second frequency problem
whereby in areas electrically weak, grid faults at distance from it could
cause rapid loss of frequency control leading to shutdown. The Spittal area
is particularly weak when Beatrice generation and other local windfarm
output routinely collapses as the weather changes. Scottish and Southern
Electricity Networks (SSEN) subsequently introduced three further bespoke
protection schemes into the Spittal design to, quote, “mitigate” this risk.
Now, a year later, a flywheel is to be added at the Moray end.
ESO was extensively criticised by Ofgem in its January report when control
of frequency was lost during the worst-in-a-decade blackout affecting more
than a million consumers in England last August involving the Hornsea
offshore windfarm.
It looks like SSEN or ESO has subsequently initiated a revisit of the design.
Press reports covering this month’s flywheel announcement carried
hyperbolic references to “trailblazing” and, from ESO, “this approach is
the first of its kind in the world and is a huge step forward in our
ambition to be able to operate the GB electricity system carbon free by
2025” .Another headline was “Giant flywheel project in Scotland could
prevent UK blackouts”. This last comment, of course, can be misunderstood
as they possess only relatively localised influence. As for “trailblazing”,
flywheel technology has been around for decades.
Detail on the proposed device is hard to find. Genetically similar rotating
devices (called synchronous condensers) to provide inertia and essential
fault current injection have already been urgently deployed at many wind
and solar farms in Queensland, New South Wales and Victoria following
blackouts, frequency and voltage oscillation problems. Lack of new system
modelling by developers was widely condemned by the Australian Energy
Market Operator (AEMO) following intervention.
Whilst device detail may have differences, the Keith “approach” claim of
“first…in world” significantly trails Australia.
Indeed, ScottishPower last October confirmed it was addressing up to seven
flywheel devices to support grid stability in south Scotland
Providing Ofgem can be convinced they are required as “infrastructure”
these further renewables support needs are financed through our bills and
the operating companies acquire the assets. Meanwhile, who is totting up
the real cost of renewables?
Given the ESO objective to “ operate…carbon free by 2025” where is the
overall UK grid master plan founded upon nationwide system studies and
modelling of inertia/voltage support/ renewables and resultant back-up
needs/ security of supply impact / capacity to future black start?And who
will prepare them?
Achieving this objective securely appears elusive.
DB Watson is a retired chartered electrical engineer
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