Liquid air storage: the answer to wind intermittency? – E-FWD (energyvoice.com)
Long-duration energy storage requires efficient, cheap and scalable solutions. Does liquid air energy storage fit the bill?
Storing energy for long periods of low renewable supply is one of the toughest nuts to crack in the energy transition.
Batteries and pumped hydro have been the main options, with green hydrogen tipped for the future. But these are either expensive, inefficient or geographically limited in scope. Liquid air energy storage is now emerging as a potential front-runner technology. Can it live up to its billing as an efficient, cheap and scalable long-duration energy storage solution?
In early June, the UK Infrastructure Bank and Centrica provided Highview Power with a £300 million loan for the first commercial-scale liquid air energy storage (LAES) plant in the UK. Centrica invested £70 million, alongside a syndicate of big investors including Rio Tinto, Goldman Sachs, KIRKBI, Sumitomo Heavy Industries and Mosaic Capital.
The plant will have a storage capacity of 300 MWh and peak output of 50 MW over six hours, making it the biggest LAES plant in the world, and one of the world’s largest long duration energy storage (LDES) facilities of any type.
Located in Carrington, Manchester, construction will begin straight away, and the facility should be complete in early 2026, supporting over 700 jobs in construction and the supply chain.
Cold energy
Liquefied air technology might sound complex but it is relatively simple. Air is super-chilled until it condenses into liquid form and can be stored in cryogenic tanks. It is then warmed and expanded to drive a turbine. A typical plant consists of three main components:
- A charging device that uses off-peak electricity to power an industrial liquefier and produce liquid air
- An energy store where the liquid air is stored at low pressure
- A power recovery unit, where the regasified air is used to drive a turbine and generate electricity
- A fourth component, an optional thermal store and proprietary cold store, can capture and store waste cold and heat from the process to improve efficiency
Air is cleaned, dried and refrigerated through a series of compression and expansion phases until the air liquefies. This is based on the Claude Cycle, which is more than 100 years old. The liquefied air is stored in cryogenic tanks that are readily available from the industrial gases industry, and at very large scale from the liquefied natural gas (LNG) industry.
The stored energy is then converted to electricity when it is needed by regasifiying the air and using the high-pressure gas to drive a turbine. No fuel is burned in the process, so there are no emissions.
Waste cold from the generation stage is captured by the cold store and recycled to enhance liquefaction efficiency. In a similar way, heat generated from compression during recharge is captured by the thermal store.
One of the key benefits is that LAES has no geographical constraints, unlike pumped hydro and compressed air, which are limited to sites with particular geographic or geological conditions.
Highview has partnered with Danish wind champion Ørsted to firm its wind energy output. “Other LDES technologies can’t go to key locations, but we can go anywhere,” said CEO and co-founder Richard Butland.
LAES has low capital and operating costs using established global suppliers. Facilities have a lifetime of more than 35 years, with proven components available off the shelf. Highview says its solution is compact with high energy density compared to other options. It is modular, flexible and scalable from around 5 MW to hundreds of megawatts and up to 12 hours of power duration.
Liquefying the wind
Liquid air technology is a contender in the race to develop solutions to store energy for long periods – from 4+ hours to days or even weeks at a time.
By capturing and storing excess renewable energy, long duration energy storage (LDES) will capitalise on inter-day peaks and troughs in wholesale power pricing by arbitraging away the difference.
It is hoped that LDES solutions will reduce costs for consumers and improve security of supply by reducing system waste. The cost of switching off wind farms – so-called curtailment payments – reached £800m in the UK in 2023.
Liquid air (LAES) can store power over days or several weeks. This makes it ideal for balancing the variability that arises when windy low-pressure weather zones pass over the country, followed by ridges of high pressure and lower wind speeds.
Butland said LAES was well suited to a wind-dominated country like the UK, where the wind is blowing two thirds of the time.
“In this type of environment efficiency is less of a factor than in solar dominated systems where batteries may work better for charging daily or between cloudy periods. We need the right technology in the right location to solve [transition] problems,” he said.
Industrial integration
LAES can operate as a stand-alone energy storage solution that captures the arbitrage opportunity between low and high wholesale power pricing periods. But its unique technical characteristics mean it can also operate alongside other thermal industrial processes, which can enhance operating performance.
For example, it can utilise waste heat from peaking gas-fired power plants or industrial chemical plants or steel mills. It can even capture waste cold from LNG regasification terminals – all helping improve round-trip efficiency.
As well as storing energy for up to several weeks, the technology will provide stability services to the grid. Over the long-term, LAES plants will facilitate replacement of fossil fuel-based power plants that currently solve for this.
Export market
Highview CEO Butland said his priority is the first phase rollout in the UK, but that the company was “particularly excited about building [a] British technology champion that can be global”.
Liquid air “has a critical place in grids globally to firm clean energy generation… We are working with big partners to take us internationally – we’ve already signed deals with Ørsted, Sumitomo and Rio Tinto, and more will be announced by the end of the year,” he said.
Sumitomo’s presence among the backers is of note, as Japan is also likely to rely heavily on offshore wind in future, although it is well behind the UK currently.
“Sumitomo is building a demonstration [liquid air] plant in Hiroshima, integrating with [an existing] LNG facility to get efficiency into the 60s% by utilising waste cold,” he said. That plant is due online in early 2025.
LAES also has smaller scale applications for industrial plants and isolated mines or processing plants that wish to switch to 100% renewable energy. Such sites cannot tap grid power and rely on local intermittent renewable supplies that, if built alongside LAES, hope to replace existing hydrocarbon backup systems.
“We have a team with Rio Tinto in Australia, which is a number of years behind UK decarbonisation, and looking to catch up. It is both aimed at microgrids and state grids – Rio Tinto is responsible for 10% of Queensland and NSW [New South Wales] state demand, as well as stand-alone projects.”
These include a Western Australia iron ore mine with a 400 MW private power system that needs expansion and storage, and a 50 MW solar plant in Northern Australia, where the LAES discharges at night.
The potential market is huge, with up to 4 GW forecast in the UK alone, according to Julian Leslie, director & chief engineer at National Grid ESO.
“Our recent Future Energy Scenarios report shows that 4 GW of liquid air storage will be required over the coming decades. Highview’s plans are welcomed to support this target. Integrating long duration energy storage into the grid is going to be vital to delivering the UK’s long term energy strategy.”
The ESO’s plans include pumped hydro and compressed air alongside LAES for longer duration to multi-day storage, and batteries for 2-4-hour balancing.
Scaling up
Highview launched the world’s first grid-scale LAES plant in June 2018. The 5MW/15MWh plant is located at the Pilsworth landfill gas site in Bury, near Manchester, and was enabled in part by over £8m in funding from the UK government.
The facility demonstrated LAES’ balancing service capabilities, including Short Term Operating Reserve (STOR) which supported the grid during winter peaks.
Highview is planning the next four larger scale facilities at strategic sites across the UK, starting with two 200MW/2.5GWh projects in Scotland and the northeast. The program has a total anticipated cost of £3 billion, and aligns with UK LDES support mechanisms as well as fulfilling the ESO’s Future Energy Scenario Plans.
These larger facilities should be operational by 2035, in line with one of National Grid’s target scenario forecasts of a 2 GW requirement from LAES, which would represent nearly 20% of the UK’s long duration energy storage needs.
Academic endorsement
David Cebon, professor of mechanical engineering at Cambridge University, said LAES was perhaps the most promising option for long duration energy storage.
“In my opinion, one of the best candidates is liquid air energy storage, as per Highview Power.” He said LAES was well developed with a high technology readiness level and pilot plants already working effectively.
He noted that both cryogenic LAES and compressed air storage use standard off-the-shelf components for energy conversion, which cuts costs.
Hydrogen would not be economically competitive with [liquid air] at any wholesale electricity price [and] it is unlikely that the fundamentals of this calculation will change.Professor David Cebon, Cambridge University
But when it came to storage vessels, LAES uses simple and cheap low pressure storage vessels, whereas compressed air requires large high pressure salt caverns. This limits siting locations and raises safety issues, as well as requiring additional energy.
Hydrogen killer?
Cebon, who is also director of the Centre for Sustainable Road Freight, said liquid air compares favourably to green hydrogen as an energy storage vector. Hydrogen has “not been demonstrated at any significant scale and is at the lowest technology readiness,” he told E-FWD.
Storage efficiency is of key importance, and LAES is vastly superior to green hydrogen in this regard. “The economics of ‘arbitrage’ electricity storage are dominated by the ‘round-trip’ efficiency of the energy storage system. Pumped hydro, liquid air and compressed air storage can have round-trip efficiencies of up to 70%, whereas green hydrogen has a round-trip efficiency of just 30%.”
The first iteration of Highview’s technology will not achieve these very high efficiencies, however. CEO Butland said their “target efficiency” is 50-60%, and efficiencies above 60% will be achieved in future iterations.
“We look at LCOE and total system benefits, and LAES has a similar efficiency to compressed air, but much cheaper and more flexible storage containers… Batteries have 80-90% but we have 40–50-year timescales with no degradation,” the CEO added.
Professor Cebon said the low efficiency and high cost mean green hydrogen “would not be economically competitive with the alternative grid-scale storage technologies at any wholesale electricity price… It is unlikely that the fundamentals of this calculation will change significantly with time.”
Keeping an open mind
Flexitricity, a UK-based demand response aggregator, said long duration storge was critical to deliver the flexibility that will underpin a net zero energy system, although it was hedging its bets on technology.
“Investment in the most promising technology types should bring costs down as adoption increases, so we are pleased to see that beginning. We encourage the new Government to move forward with the next steps of the Long Duration Energy Storage consultation as a no-regrets action,” the company told E-FWD.
Julio Dal Poz, managing director, energy transition practice at FTI Consulting, believes LAES’s advantages are less clear-cut.
“There is value in having a range of available energy storage solutions and we should try to make the most out of our existing assets,” he told E-FWD.
“For example, we can design long-duration energy storage solutions to [use] existing lakes and mountains, when possible, in the case of pumped hydro or use existing depleted underground reservoirs to store compressed air or hydrogen. This could provide more scale and a potential competitive advantage versus newbuild storage tanks for liquid air.”
“On the other hand, liquid air could potentially provide a higher energy density in some cases, so we need to understand better the full solution costs, including storage and transport to see what technology really provides better value for money.”
Tech neutral policy
LAES faces competition from new technologies. For example, a team from Stanford University in the US has conducted research on using liquid organic hydrogen carriers (LOHCs) as a means of long-term renewable energy storage.
LOHCs – or liquid batteries – store hydrogen using catalysts and increased temperatures, before releasing it as electricity when needed. The discovery uses a catalyst called cobaltocene in the reaction to store and release the energy without releasing hydrogen gas. Development is in its early stages but the tech shows potential.
To make room for future innovation, Dal Poz said that any policy framework for encouraging LDES should be technology neutral.
“At this stage we should not try to be prescriptive and dictate which type of long-duration energy storage technology will be the most efficient in terms of value for money, grid stability and energy security.”
Development of new LDES solutions should be supported by a market mechanism that directs investment towards the most cost-efficient technologies.
The UK is currently consulting on a cap-and-floor mechanism “similar to what is currently available to interconnectors between the UK and other European countries.” It is also similar to the Contract for Difference regime for offshore wind, which balances risk and value for both investors and consumers.
“This would allow the market to develop and to choose the most effective technologies,” Dal Poz concluded.