Energy Storage is many-faceted, it's real and it is going to be very big - inevitably!

Professor Seamus Garvey

Professor Seamus Garvey reflects on the outcomes of the UK Energy Storage conference that took place earlier this year at the University of Nottingham.

"One thing is certain about the inevitable – it will eventually happen! UKES2024, the 2024 instance of UK Energy storage conference, took place at the University of Nottingham from April 10 – 12 of this year. Like every conference, UKES2024 had its own quite unique flavour and its own very singular core message. That core message can probably be summarised as: Energy Storage is many-faceted, it’s real and it is going to be very big - inevitably!

A strong section of UKES2024 was dedicated to hydrogen and its role in storing and carrying energy. Many other discussions address hydrogen separately from energy storage and yet its only other roles are small by comparison. On Friday 12^th, one of the three parallel streams of UKES2024 was dedicated to the underground storage of hydrogen and this session was also co-badged as Hydrogen Storage in Caverns 2024 (HSiC2024). HSiC2024 was characterised by a real sense of willingness and excitement to get on with it. The presentations included an impressive assessment of the real potential of the Rough depleted gas reservoir (owned by Centrica) to act as a massive hydrogen store for the UK – hosting around 16TWh(LHV) of the gas. This alone represents 10 - 20% of the hydrogen storage that will be needed in a cost-optimised Net Zero UK. A separate presentation from DEEP.KBB was very revealing about the amounts of energy required to realise caverns in bedded salt. Evidently the energy required to realise a large salt cavern is less than the energy that would be lost in a single cycle of the resulting energy store – and even then, the action of making the cavern has a significant compensation in that it releases many hundreds of thousands of tonnes of mineral salt that has potential value in its own right. A keynote talk from British Geological Survey confirmed that the UK theoretical potential for developing storage in salt caverns runs to multiple tens of thousands of TWh(LHV) – far more than we will ever need. The UK is very well endowed with bedded salt resource.

No energy storage conference could be complete without having numerous presentations about batteries. In UKES2024, the emphasis was towards pushing up performance whilst controlling costs. A keynote address from an Oxford University electrochemist highlighted the significant potential for further increases in battery energy density. Multiple talks affirmed the strong progress that continues to be made on cost-reduction for batteries for the low-end EVs and noted that one (Chinese) EV can now be sold at profit for <£10k. The soluble lead flow battery featured in another keynote and was striking due to its high sustainability and maintainability. Said batteries have low capital costs per kWh - though not the lowest of all. However, these batteries never die and they offer a solution for distributed energy storage whose long-term affordability and sustainability are perhaps second to none.

UKES2024 was especially strong in terms of content relating to Medium Duration Energy Storage (MDES) technologies – mostly thermo-mechanical energy storage propositions based on compressed air, liquid air or pumped thermal energy storage. These units typically feature discharge times between 4 and 200 hours. These technologies are squeezed between hydrogen on the one side (the long duration side) and batteries on the other side (the short duration side). A keynote entitled Monetising Energy Storage gave a very vivid visualisation of how the MDES technologies will be squeezed by hydrogen on the long-duration side and by batteries on the short-duration side. It crystallised the urgent need to find a way for the MDES technologies to travel down the learning-by-doing curve. The journey between the present state of cost and performance and the future states that we know (from engineering science) to be achievable is an especially difficult one for the MDES technologies because both good performance and competitive cost depend critically on building large-scale units. A 300MW compressor cannot be built as a large collection of identical small units in quite the same way that a 300MW electrolysis plant might be built or the same way that a (300MW, 150MWh) battery energy storage system would be developed. Some way must be found by which classes of large machine design can be evolved without huge risk to the developers and then those designs can perhaps be licensed very widely at low cost. The keynote address from an eminent engineer based in China and connected to all of the major compressed air energy storage (CAES) projects there relayed the high ambition for CAES in China: 123MW of power is already associated with operational CAES plant introduced since 2020 and a further 1200MW of CAES plant is currently under construction.

Integration and the coordinated action of subsystems percolated through every session. The advent of AI and high-bandwidth communications is opening-up a range of flexibility options that would not otherwise be possible. Distributed energy storage units within the electricity distribution networks clearly have potential to play a huge role in deferring network upgrades – especially when these are operated in a coordinated way. Monolithic energy stores sited at critical points in the transmission network can serve the combined functions of (1) acting as storage assets for the country as a whole and (2) helping to resolve power transmission bottlenecks (especially the well-known North-South constriction). Smart tariffs for domestic and other customers also show promise for unlocking swathes of additional flexibility resource over fairly short timescales (typically 1 – 6 hours) at very low marginal cost that will be invaluable in our future Net Zero electricity system. In this conference, it was especially evident that the nexus between space heating and flexibility in the future electricity system will become increasingly important. Much more focus is needed on ensuring that electrically-driven heat pumps operating at the coldest times in Winter can (a) still achieve a reasonably-good coefficient-of-performance and (b) be run flexibly with in-property thermal storage serving to smooth-out the heating delivery within the target spaces. Thermochemical energy storage is emerging powerfully to complement and even displace phase-change materials in the latter domain. Salt/water pairs serve the lower temperature end, oxide/hydroxide pairs fit in the middle and high temperature thermo-chemical storage was reported based on using metal/metal-oxide (or metal-oxide/carbonate) pairs.

Unsurprisingly, the central roles of policy and market structure came up for discussion very frequently. Some of the existing structures incentivise behaviours that are not at all conducive to our progress towards net zero. Two cases of note were: (a) existing rules on the use of energy storage systems within networks that preclude the exploitation of the full range of charging and discharging powers of flywheel energy storage systems and (b) the charges made by networks incentivising plant delivering flat demand over those that can produce truly flexible demand. A very broad observation made in the final discussions of the conference seemed to resonate with everyone: that with our present political system, policy is precisely as transitory as its political proponents. There is, at least arguably, a need for energy policy to evolve on timescales much longer than a single term of office. There was a call, during the closing session of UKES2024 for policy to have some transparent link to models of the future energy system. Multiple parties can now understand and run such models if the datasets (time-series data for assumed demand and supply) are made available.

The time and place for UKES2024 could hardly have been more appropriate. Delegates were able to look out the window of the conference venue to see Ratcliffe-upon-Soar power station consuming the last coal that will be burned in the UK for power generation prior to the disappearance of coal-fired generation in September of this year. Some were also aware that electricity prices across Europe had been zero or negative for sustained periods of time during the week of the conference: 15 consecutive hours in the UK on April 6^th-7th, and prices were negative again in the afternoon of the last day of UKES2024. These negative prices arise when low-carbon generators are providing most or all power and when additional thermal power plant are also being run to provide system stability. The UK power grid had set a new record low carbon intensity of 21gCO2/kWh on April 5th – and then broke that record on April 15th when it fell to 19gCO2/kWh. These figures will fall again when the Ratcliffe station finally shuts down. Suitably dimensioned energy storage will replace the firm capacity provided by plants like that, charging on low-cost low carbon energy harvested in periods of surplus renewable energy generation.

There are some inevitabilities about energy storage alright:

1. Virtually every energy storage solution will find a substantial and lucrative niche to serve in our Net Zero future
2. The scale of UK spending on energy storage over the coming few decades will be in the hundreds of billions of pounds – similar in magnitude to the spending on the new renewable energy generators

It is possible, but far from inevitable, that the UK itself could become a powerhouse of energy storage technology – directly utilising its own offerings in the first instance and subsequently exporting these worldwide. For this, we need firstly to understand closely where our intrinsic market needs best map onto our innate energy storage capabilities and then we need our policy makers to catch up with the vision of this amazing community." 

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