The Royal Society – Written evidence (LES0014)


The Royal Society is the national academy of science for the UK. Its Fellows include many of the world’s most distinguished scientists working across a broad range of disciplines in academia, industry, charities and the public sector. The Society draws on the expertise of the Fellowship to provide independent and authoritative advice to UK, European and international decision-makers.


The Society’s fundamental purpose, reflected in its founding Charters of the 1660s, is to recognise, promote, and support excellence in science and to encourage the development and use of science for the benefit of humanity. Our strategic priorities therefore are to promote excellence in science; to support international collaboration; and to demonstrate the importance of science to everyone.



1. How much medium- and long-duration energy storage will be needed to reach the Government’s goal of a fully decarbonised power grid by 2035 and net zero by 2050, and by when will it need to be ready?


The Royal Society report, Large-scale electricity storage, identifies that many tens of TWh of energy storage capacity will be needed to support a Great British electricity system fed mainly by wind and solar energy, even when other generating technologies such as nuclear are included. The report is available at


By 2050, Great Britains electricity needs could be met entirely by wind and solar supported by large-scale storage. In this case, which we are not advocating, up to 123 TWh of energy storage capacity would be needed to ensure electricity supply meets demand even during rare widespread or prolonged instances of insufficient wind and solar supply. Including other technologies like nuclear or retaining some gas (methane) plus CCS reduces the requirement for storage but it remains high at tens of TWh.


The scale of storage needed in the UK is over 1000 times that currently provided by pumped hydro and is far more than could be provided by conventional batteries.



Electricity systems with a high proportion of wind and solar generation are sensitive to extreme weather events, beyond diurnal and seasonal variations. GB’s electricity system will be impacted by three main types of extreme weather:


Table 1: Weather stress events

Stress events



Summer wind drought – frequent

One full day of very low wind speed in summer

Once or twice per year

Summer wind drought – infrequent

Up to four weeks of very low wind speed in summer

Once every 10 years

Winter wind drought

Up to a week of very low wind speed in winter

Every few years


The greatest challenge to renewable systems is posed by winter wind droughts because they coincide with periods of low temperatures that lead to high energy demand, as well as lower solar irradiance.


Wind has greater year-to-year variability than solar. The Met Office has advised that while climate change is expected to lead to increased volatility in the wind, the effect will be less than the interannual volatility that is seen in the 37 years that was used to model the need for storage (there is a small probability that climate models may miss potential tipping points and seriously underestimate the impact of climate change on temperatures and sea levels, as well as on wind and solar irradiance).


The 37 years studied probably do not sample the full range of variations in wind speeds. We include 20% contingency in the requisite storge capacity to allow for this. Studies that look at individual years (as some do), or even a few decades of weather data, are likely to very seriously underestimate the need for storage, and overestimate the need for alternative flexible sources of elecricty (such as gas + CCS).



The Royal Society’s study of storage, which is focused on the net zero era, uses the hourly profile in a model (provided by AFRY) of 2050 demand of 570 TWh (before transmission and distribution losses). Levels of 440 and 770 TWh were also studied. This is consistent with projections in the National Grid’s Future Energy Scenarios and those made by BEIS.


The 570 TWh/year in AFRY’s model comprises base contribution 355 TWh, heating 96 TWh, and EV charging 119 TWh.



2. How sensitive is the amount of storage needed to assumptions about the future balance of supply and demand on the grid?


The Royal Society finds that the need for storage, and the level of wind and solar generated electricity that will be needed, is proportional to demand, but the expected average cost of electricity is not very sensitive to this level as storage is only required to meet approx. 14% or demand.



Both nuclear and gas with CCS could be used as a baseload. This would provide a constant amount of reliable energy supply, therefore reducing the amount of wind and solar supply needed, and in turn the amount of storage. Nuclear and gas are expensive to run flexibly to respond to fluctuations in supply or demand. The Royal Society report uses BEIS’s projections that:

                     Nuclear will cost £66-99/MWh (with 90% load factor)

                     Gas with CCS will cost £78-85/MWh (with 92% load factor): this estimate is very sensitive to the assumed cost of gas.


Adding baseload will increase the cost of electricity provided by wind, solar, and storage. This is because, although the demand that wind, solar and storage will have to meet will be smaller, it will be more volatile as baseload removes a constant amount. It follows that the cost of electricity will only be reduced by adding a baseload if the cost with baseload is lower than the average cost of electricity without baseload.


BEIS’s central projection that gas with CCS will cost £82/MWh in 2040 is towards the top of the range of the estimated cost of electricity without baseload. Baseload gas with CCS is therefore unlikely to lower the cost of electricity. Adding enough flexibly operated gas with CCS to replace all storage would lead to higher costs and unacceptable levels of GHG emissions. It is possible, however, that using gas with CCS to provide some of the flexibility needed to match wind and solar (most of which will be provided by storage) could lower costs. Whether or not this will be the case is sensitive to many factors that are very hard to predict. Gas is also subject to price volatility and energy insecurity, to a greater extent than wind, solar and storage.


Bioenergy, with or without CCS is also capable of meeting a significant proportion of demand; up to 50 TWh/year without imports. However, it is expensive (BEIS projects £182 – 211/MWh with CCS) and has broader challenges around the imperative for responsible sourcing as well as potentially substantial air quality implications. If used with CCS, it has the potential to be carbon negative, so it could attract carbon credits that would lower the cost.


Pumped hydropower, which delivered 5.5 TWhe in 2021 in the UK, offers good flexibility to match variations in wind/solar supply and demand. However, its potential capacity is limited in GB and it will therefore not have a significant impact on the need for other forms of storage



Upgrades to interconnectors across Europe could help smooth supply fluctuations driven by weather. However, the weather across the British Isles and over Europe is linked. Intra-UK or pan-European interconnectors are therefore vulnerable to wind droughts, cold periods, widespread cloud cover and water shortages at the national or continental scale respectively. They are also subject to political factors. It would therefore be prudent to create a GB system that can cope when imports are not available.


There is an opportunity for exporting surplus electricity through interconnectors. The volume of imports and exports will depend on renewable capacity in GB and across Europe. Since GB has a very large wind resource, it is possible that it could be exporting on a 100 TWh scale in 2050, while also importing solar energy from southern Europe.



Conventional demand-side management that are used to smooth out peaks in electricity demand, cannot provide help in dealing with the longer-term variations in wind and solar supply that pose the major challenge for storage. However, it has recently been shown that cutting demand by small amounts in period when a few months of low wind speeds are forecast can have a significant impact on the need for storage (an analysis of this possibility is reported in a Stop Press in the Supplementary Information to the Royal Society report).



The electrification of heat will lead to a much larger difference between winter and summer demand (which will be slightly offset by greater demand for cooling). However, a mixture of 80% of electricity provided by wind and 20% by solar will mirror this difference when averaged over many years, although there is huge interannual variability: volatility not seasonality is the issue.



3. Which technologies can scale up to play a major role in storage?


Hydrogen will play a major role in long-term energy storage. It has a low round-trip efficiency, but its low cost per unit of storage capacity makes it the leading candidate for storing energy for long periods. The UK has a more than adequate potential for underground hydrogen storage, although it is spatially limited to East Yorkshire, Cheshire, and Wessex.


Ammonia may also be useful for long-term storage, but it is unable to compete with hydrogen due to cost (it is estimated that using ammonia to provide all storage instead of hydrogen would increase the average cost of electricity by at least £5/MWh). However, it may be useful in areas which cannot store hydrogen underground. Ammonia is also much easier to transport than hydrogen, which would likely need to be produced and converted to electricity close to storage caverns.


There are many other viable forms of storage which can play a role over short to intermediate time scales. Most are at a low technological readiness level, and therefore would benefit from further R&D and need to be demonstrated at scale. ACAES, thermal and pumped thermal storage, thermochemical storage, gravitational storage, and storage designed to deliver heat could potentially store TWhs of energy, using multiple distributed units. These technologies are potentially low cost (relative to batteries), have low self-discharge rates and potentially good round-trip efficiencies. Thermochemical is the only one of these technologies that may be viable for very long duration storage but remains at an early stage of development, and is not best suited to storing electricity.


Some small-scale storage which can respond rapidly is also necessary. Batteries will continue to fulfil this need. While they are highly expensive, they are also very efficient and can respond rapidly to fluctuations in demand. In costing electricity the Royal Society report assumes that 15 GW will be needed by 2050 to provide rapid response, which should be more than adequate,.


Table 4 from the large-scale electricity storage report provides further information.

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Please see the table above, in which storage technologies are divided into different categories according to how frequently the stores have to be cycled to recover the investment.


In the long-term category, hydrogen is the cheapest option. The report uses the H21 NE consortiums study of storing hydrogen in caverns of 300,000m3 each, which would be combined to form clusters comprising 10 caverns. H21 NE estimate that each cavern could house 122 GWhLHV of useable hydrogen. Using only hydrogen to meet the need for storage in a high wind and solar energy system with no baseload, would require 85 clusters of 10 caverns (without contingency capacity). Building this many by 2050 would be challenging, but the technical capabilities to undertake such projects exist in the UK.


Hydrogen, potentially supported by ACAES and/or some other forms of relatively efficient ‘medium-term’ storage, with some batteries for grid stability, is expected to offer the most viable and cost-effective approach to storage in GB.


There are a variety of storage options available but, in many cases, they are at a low TRL and may not provide much storage capacity in isolation.



Refer to table 4 above.



It would be possible to produce enough hydrogen from wind and solar to meet the UK’s long-term energy storage needs. There is also adequate capability to store hydrogen in underground solution-mined salt caverns, though their locations are geographically limited.


There would also be co-benefits in producing additional green hydrogen beyond the level needed for storage. It is expected that there may be tens of TWh of demand for green hydrogen for other services, which would lower the cost of green hydrogen for storage and therefore reduce electricity costs.



Storing heat can reduce the demand on electricity systems and therefore could play an important role in shifting the electricity demand away from peak hours. However, heat networks in the UK currently only provide 2% of the UK’s heat (whereas in some European countries, such as Denmark, local heat networks meet over 50% of water and space heating demand).


Thermal and pumped thermal storage and thermochemical storage could potentially deliver some TWh of energy, which in isolation would not meet GB storage needs. Technologies include water pit storage, molten salts, and Carnot batteries. Most would use multiple distributed units with storage capacities up to multiple GWh and outputs from a few kW to hundreds of MW. Heat storage may prove to be a low-cost storage option and have good round-trip efficiencies. Most thermal storage technologies are at an early stage of development and would benefit from further research as well as demonstration at scale to prove their efficiency.



4. What policy support is currently in place to support deployment of storage technologies? Is it sufficient to support deployment at scale?



There is a good economic case for long-duration energy storage: the alternate paths to a low carbon electricity system are expected to be more expensive. Using only wind and solar supply, supported by hydrogen storage (and some batteries for grid stabilisation), would lead to an average cost of electricity fed into the grid in 2050 between £52/MWh and £92 MW/h, in 2021 prices (based on the range of assumptions used in the Royal Society report). For comparison, the wholesale electricity price hovered around £46/MWh in the last decade , but for most of 2022 it was over £200 MW/h. Building renewable energy and storage systems in Great Britain will also enable greater sovereignty and protect against fluctuations in the price of imported energy.


Building the storage needed in GB will require substantial financial investments. The report notes that price differentials in wholesale and balancing markets may incentivise the construction of significant amounts of short-term storage, but new mechanisms, including forms of guarantees, will be needed to make investment in large-scale, long-duration storage attractive. There will also be a need to facilitate far greater cooperation between generators and owners of storage in scheduling charging and dispatch of energy from different types of stores. The report suggests that the current GB wholesale market arrangements, in which long-term investment decisions and short-term dispatch are largely governed by a single price signal, will not be able to meet these needs.



To enable the development of the storage necessary to underpin a wind and solar dominated grid, the transmission grid will need to be enlarged (to connect new sources of electricity to new storage sites) and strengthened (to deal with large fluctuations and higher peak loads).


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5. How well developed is the UK industry across different storage technologies, such as hydrogen or redox flow batteries? How does the UK compare to global competitors in these industries?


Refer to Table 4 above.



The UK has expertise in many of the technologies needed for hydrogen storage. The construction of large hydrogen storage systems (which must start soon if he UK is to meet its climate targets) would foster the development and drive down the costs of technologies for which there are potentially large export markets


Export potential could also be realised by transmitting surplus electricity through interconnectors, which will depend on generating costs when there are surpluses, and renewable capacity in GB. GB has a large wind resource and it could be exporting on a 100 TWh scale by 2050, while importing solar energy from southern Europe in periods when wind is low.


Of the considered storage media, there may be a potential for hydrogen or ammonia export,



See answer above.



6. Beyond the cost of deploying long-duration energy storage, what major barriers exist to its successful scale up (e.g. the availability of a skilled workforce, the ability to construct the necessary infrastructure on time, or safety concerns around new technologies)?


Developing the number of caverns needed to meet GB’s storage needs by 2050 will be challenging, but the UK has the technical capabilities to complete such projects. The report points out that studying further the possible barriers to the rapid construction of such caverns would be a useful next step.


There needs to be a holistic approach to developing the storage required. It isn’t just a question of inviting bids to build and operate say a hydrogen store. Consideration must be given to grid reinforcement and connection, electrolyser and turbine installation, the skilled workers needed to construct and operate a safe storage facility.




It is expected that a cluster of ten caverns of 300,000 m3 each could be constructed in 5 years, if the caverns are solution-mined in parallel. 85 clusters will be needed by 2050. Achieving this is challenging but possible by 2050 if a start is made in the very near future. It is important to recognise that we do not require all the storage capacity to be built in one step. It can be ramped up, but the rate of ramping needs to be as fast as possible.



7. What steps should the Government take now to ensure this storage can come online later in the current decade?



Yes. A number of other countries face broadly similar challenges in decarbonising their electricity systems. However, there are difference starting points, for example France is a much higher contribution from existing nuclear. The UK has a surplus of wind but less solar than others farther south.


Ways to foster the use of hydrogen are being actively studied in many countries, but we have not analysed the ideas that have been proposed.


11 September 2023