The role of long-duration electricity storage for net zero

Reaching and maintaining a net zero society may require market reform to incentivise the build-out of long-duration electricity storage.

A major academic study analysing the role of long-duration electricity storage in Great Britain reaching net zero could provide lessons for Northern Ireland in long-term planning for electricity grid stability.

Great Britain has a more ambitious target of decarbonising its electricity system completely by 2035, on the recognition that the electrification of heat, power, and transport will be the main drivers of net zero by 2050. Although not as far-reaching, Northern Ireland’s target of 80 per cent of electricity consumption from renewable sources by 2030 is equally challenging.

To meet these targets, wind and solar, as the recognised cheapest forms of low-carbon generation, will lead the decarbonisation of electricity. However, the challenge lies in the volatility of these two forms of generation and the need for this volatility to be complemented by other flexible low-carbon sources and/or energy storage, if grid stability is to be ensured.

Large Scale Electricity Storage, a report compiled by the Royal Society, has modelled wind and solar supply against demand over an almost 40-year period, using real weather data, and highlights the significant gap that will need to be plugged if security of supply is to be maintained.

The report details how the availability of wind and solar power varies on time scales ranging from seconds to decades, depending on the weather. Demand is also variable, and mismatches between supply and demand occur on time scales ranging from milliseconds to years.

“As there are times when the sun is not shining and the wind is not blowing, wind and solar supply cannot meet demand directly on their own, however much generating capacity is installed,” the authors state.

In short, if relying on wind and solar generation, balancing supply and demand would require tens of terawatt hours (TWhs) for over several decades. While Northern Ireland’s storage requirement will not be as high, the underpinning need for storage beyond short-term balancing is recognisable.

As renewable generation from wind and solar has increased in recent years the need for storage capacity has been recognised, however, much of the focus has been on battery storage, in the context of stretching near-term electricity decarbonisation targets.

While batteries will play an increasing role in providing short-term balancing, the costs of utilising batteries alone to bridge the long-term mismatch between supply and demand is unrealistic when considering the cost of investment in a technology with a lifespan of around 20 years.

The report groups storage technologies into three categories according to the typical time in which their contents must be cycled:

1. Minutes to hours: conventional (non-flow) batteries;
2. Days to weeks: flow batteries, advanced compressed air energy storage, Carnot batteries, pumped thermal storage, pumped hydro, liquid air energy storage; or
3. Months or years: synthetic fuels, ammonia, hydrogen.

Meeting the demands of net zero will likely require deployment of technologies within all three groups, and the implications on the cost of electricity will be determined by the scale of deployment. Renewable generation provided directly to the grid will invariably be the cheapest form of electricity, with electricity provided by storage costing more. However, meeting the need for long-duration storage will require very low cost per unit energy stored.

Market reform

As the report’s authors point out, in current wholesale electricity markets, both long-term investment decisions and short-term dispatch are largely governed by a single price signal and this is a challenge for long-term investment because of future price uncertainty.

“The large-scale long-term storage that this report finds will be essential, could never recover its capital costs in such a system since it will be idle much of the time. Existing markets and regulations will also not be able to deliver the operational coordination between wind and solar generators and operators of storage that will be needed to schedule the use of different types of store cost effectively and ensure that they do not become empty. There is an urgent need to recognise these problems and explore possible solutions.”

In short, the report finds that current market structures may incentivise the construction of significant amounts of short-term storage, however, new mechanisms, including forms of guarantees, will be needed to make investment in large-scale, long-duration storage attractive.

It adds: “To contain storage costs, generators and owners of storage will have to cooperate to an unprecedented degree in scheduling charging and dispatch of energy from different types of store. Ensuring this cooperation is likely to require radical reforms.”

While the report’s focus was solely on great Britain, correlations between Great Britain’s island electricity market, and the all-island Single Electricity Market (SEM) can be drawn. Northern Ireland’s demand and supply will be lower than that of Great Britain but will ultimately face the same challenges of addressing the long-term mismatch of supply and demand in an electricity system largely powered by intermittent wind and solar.

As the Department for the Economy prepares to publish a new renewable electricity support scheme (RESS), aimed at increasing levels of renewable electricity, increased use of battery technologies will be the leading technology in providing grid stability in the push to achieve the 80 per cent electricity consumption from renewables by 2030 target.

Increasing interconnection with the Republic will be critical to maximising increased renewable generation across the island, and utilising storage options on a larger geographical area.

As too will policy decisions on the technologies which could and will be deployed to best meet the needs of Northern Ireland’s consumers. The Large Scale Electricity Storage report indicates the need for consideration of short; medium; and long-duration storage options to meet the demands of net zero by 2050 and beyond. Incentivising these technologies will require significant market reform.