On islanded (or isolated) grids with growing renewable penetrations, grid operators often struggle to maintain system stability. Operators in places as diverse as Ireland, Puerto Rico and Australia frequently rely on inertial response from thermal power plants like coal or gas-fired generators to balance sudden mismatches between supply and demand.

However, recent research from Northern Ireland’s Queens University Belfast (QUB) finds that battery-based energy storage can provide inertial response for system reliability much more efficiently, at a lower cost and with substantially reduced emissions than a much larger quantity of thermal generation.

QUB’s research found that just 360MW of battery-based energy storage could provide the equivalent stabilisation to Ireland’s All-Island electricity system as would normally be provided by 3GW of conventional thermal generation. That shift to batteries could save up to €19 million (~£16.9 million) annually and could achieve approximately 1.4 million tonnes of annual CO2 savings.

Inertia: A blink-of-the-eye grid balancing service

Inertia is a system-wide service that responds to fluctuations in electricity frequency in the first fraction of a second of an imbalance between supply and demand – for example, when a power station suddenly drops offline. Traditionally, this stabilising hand has come from the kinetic energy provided by the spinning mass of (synchronous) generators that produce electricity from fossil fuels.

All this occurs well within the first half a second of an issue – literally, the time it takes a human eye to blink. Traditionally the electric power sector has not thought of it as service. It’s just part of the physics of synchronous generators; and we don’t miss something until it’s gone.

As the proportion of energy from (non-synchronous) wind and solar grows this source of traditional ‘analogue’ inertia is in increasingly short supply. The typical solution to this has been to hold back wind and solar output during such times, but this is growing increasingly costly as renewable penetration grows. Let’s face facts: paying not to use zero-fuel cost and zero carbon renewables isn’t a tenable solution in the long run; and would require a significant overbuild of renewable capacity to achieve the same decarbonisation targets.

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The Department of Business, Energy and Industrial Strategy (BEIS) has refused to provide any clarity over when a decision on the potential derating of energy storage assets within the capacity market (CM) will be made despite a senior policy advisor stating the judgement is “imminent”.

In July BEIS proposed significant changes to how their generation classes are de-rated within the CM, suggesting that the majority of storage assets could lose their current 96% de-rating status in place of a mechanism designed to reflect the discharge duration of assets in the instance of a stress event.

With the exception of a methodology update in September, no further notices have been issued. Since this time, storage developers have entered their projects into pre-qualification for the next CM auctions scheduled for January/February 2018, with no knowledge of whether their applications will be affected by the rule change.

Speaking at Tuesday’s Solar Trade Association (STA) Market Access and Systems Integration conference, Alexander Berland told Clean Energy News the decision would soon be forthcoming.

“A publication is imminent; we are expecting a decision on that to be very soon. We do want to give clarity as soon as we possibly can as important decisions on investment are relying on that,” said the senior advisor for smart energy at BEIS.

He added that this information had come from the government’s security of supply team who govern the CM.

When asked to elaborate today on Berland’s comments, BEIS refused to clarify when this “imminent” publication would be issued, adding only that the department “will be publishing in due course”. The department would not be drawn on if this would be before the T-1 auction to be held 30 January or the T-4 auction on 6 February.

A number of developers have expressed concern that the rules may be implemented ahead of these dates, severely impacting the business case used to build their applications.

One developer that submitted at least two projects into CM pre-qualification told CEN in September that to do so would “lack common sense”, as it would see a number of projects likely pulled from the CM at a time when government has expressed its intention to promote energy storage.

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