How liquid air can store solar and wind energy

Storing energy from solar and wind is a huge challenge. We talk to Highview Power, whose liquid air concept means solar and wind farms can store energy for the long term.

Forward: features are independent pieces written for Mewburn Ellis discussing and celebrating the best of innovation and exploration from the scientific and entrepreneurial worlds.

The Sunnica Energy Farm in Suffolk is planned to cover 2,500 acres, enough to power 172,000 homes. Planning consent is not yet given. A major sticking point? The way Sunnica will store excess electricity. It’s not clear what technology will be used. Lithium-ion? Redox flow? Local residents have triggered two reviews partly stemming from the uncertainty.

How best to capture the energy produced by solar and wind farms is a global debate. When the sun shines and the wind blows, power output surges. Later, in times of stillness and darkness, the grid needs to draw on reserves.

There are five main methods of storing electrical energy. Electrochemical batteries such as lithium-ion and redox flow are the current default, but expensive. Pumped hydro sends water uphill during times of energy generation, which is then released to flow through turbines to a lower reservoir when needed. There are mechanical stores, relying on gravity or momentum – raising weights or spinning up flywheels. Creating hydrogen through electrolysis. And, finally, thermal and phase transition: turning air into a liquid or heating sand to 500°C to store heat – pioneered rather counter-intuitively by Polar Night Energy in western Finland.

Grid scale storage is urgently needed. Demand for storage is forecast to grow from 60GWh in 2022 to 840GWh. The US alone is looking at a six-fold increase in demand. The world needs a way to store energy on a grid scale.

So what’s the answer? A leading candidate is Highview Power’s liquid air concept. By cooling air to -195°C and storing the liquid in tanks, the company offers an alternative to lithium-ion or redox flow batteries. The company claims there is no way to hit net zero without its technology.

‘Air is cleaned and dried,’ explains Richard Butland, the CEO of Highview Power. ‘Then it is refrigerated by compression and expansion stages until it liquefies. The liquid air is stored in tanks. When power is needed, the liquid is pumped at high pressure and heated, so expands, and drives a gas turbine to generate electricity.’

This method is known as the Claude cycle, invented by French engineer Georges Claude a century ago.

There are some big advantages to this method. The equipment used is standard, proven kit. Nothing fancy. The turbines are from the gas industry. The storage tanks are from the LNG sector. This means the components are market ready and can be produced at scale. This is an asset for a solution aimed at grid-scale deployment.

A secondary system improves the performance of the process. Molten salt is used to capture heat that would otherwise be wasted, and gravel to store excess cold. ‘This dramatically increases efficiency,’ says Butland. ‘We have an overall round-trip efficiency of over 50%, even in the first generation of our plants. That is our signal achievement. We can push that number up.’

The capacity is large. ‘At the moment, one of our plants with full tanks stores 2.5GWh. We can charge quickly through the day, and then supply 200MW for up to 12 hours through the night. Or as little as 5MW for longer periods.’

The technology is modular. It is possible to add more cryo tanks to store more liquid air or select a different turbine size to increase output. Unlike lithium-ion, there’s no danger of a fire.


So, is Highview competing with other technologies to be the answer to grid-scale storage? ‘No,’ says Butland. ‘The reason is that it is going to take all of these technologies to make a dent in the problem. We need terawatt hours of storage. Most will find a niche. If you look at Gravitricity or pumped hydro, they are brilliant technologies, but are very location specific. Gravitricity needs deep caverns to drop weights into. Compressed air technologies, which we are seeing in places such as Broken Hill, Australia, need mines to fill with compressed air. Pumped hydro needs reservoirs. They are good, but niche.’

For reference, total global manufacturing capacity for lithium-ion batteries reached 1TWh last year. Electricity demand in the UK alone in 2022 was 275TWh, of which 40% was supplied by renewables. Storage is in its infancy.

Delve deeper and the Highview proposition becomes even more convincing. It has the ability to address grid intermittency. ‘Wind is like a hosepipe,’ says Butland. ‘What you put in has to come out the other end. The grid is constantly battling to balance surges and slumps in supply. Forty per cent of UK generation today is wind and it simply can’t be used most of the time. So the UK is wasting 3TWh of wind a year, which is enough to power a sizable city. It’s costing the grid more than a billion pounds to pay the wind farms to switch off. Intermittency is a massive, massive problem, which we can address.’

A second problem for the grid is the location of power generation. Coal and gas power stations can be located around the country. ‘The next generation of supply – wind and hydro – is going to be located at a greater distance, so the transmission networks need to be rebuilt. We are able to build storage plants anywhere needed.’ The absence of any fire risk should make planning approval easier to win.

And the third advantage is stability. Butland explains: ‘Grids need to be resilient. They need voltage management and to have an array of backup capabilities that can be brought to bear at a moment’s notice. There is a £3bn market delivering reactive power services into the grid. And 80% of these services today are by fossil fuel power stations, which are set to be decommissioned over the next decade. Solar and wind won’t be able to replace these services. So those are the three challenges: intermittency, geography and stability. And the solution needs to be able to work at grid scale.’ Highview in theory can nail all these, bringing smooth energy release, where needed, whenever the grid requires.

Highview is now scaling up, having raised over £300m. ‘We are not just a technology company, we are a delivery company,’ says Butland. ‘Our first renewable power station, which we are building in Carrington near Manchester and will be operational by the end of 2026, will charge at 50MW and store 300MWh. Planning is also now commencing on four large-scale 2.5GWh facilities at strategic locations across the UK.’

The company has been refining its liquid cooled air concept for 17 years now, enjoying £25m in funding before its latest round. The Manchester plant will require approximately £250m of investment. Then the plan is to build out the new large plants over the next few years. That mission needs £10bn in funding. ‘We can deliver 45GWh a year of storage capabilities in a decade,’ says Butland. ‘That will make a serious dent in the net-zero challenge.’ Other grids Highview Power is talking to include Australia, where a facility to store solar energy is in the planning stages in the Northern Territories.

Highview offers a market-ready, proven technology, able to offer true grid-scale storage. Plants can be built on any plot of land. The components are standard gas industry hardware. As Butland says, other technologies such as redox flow batteries have their place. The economics is complex, depending on variables such as component costs and the performance of rival technologies.

But for sheer storage capacity, anywhere energy is needed on demand, Highview Power’s liquid cooled air is a formidable proposition.



Liquefied air set to become essential part of energy storage landscape

Callum McGuinn, Partner and Patent Attorney at Mewburn Ellis, comments:

“With their liquefied air technology, Highview Power are offering a tried-and-tested, modular and versatile solution to smoothing out the intermittent nature of renewable energy supply. It is clearly unsustainable to be wasting terawatts of wind power annually due to the serious lack of grid-scale storage in the UK. Investment in renewables needs to be matched by investment in grid-scale storage, and liquefied air is set to become an essential part of the energy storage landscape alongside more traditional technologies like pumped hydro.”



Written by Charles Orton-Jones