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