Liquid air 'offers energy storage hope'

Electricity pylon and wind turbines (Image: PA) Renewable power generation, such as wind turbines, can produce electricity when it is not in demand

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Turning air into liquid may offer a solution to one of the great challenges in engineering - how to store energy.

The Institution of Mechanical Engineers says liquid air can compete with batteries and hydrogen to store excess energy generated from renewables.

IMechE says "wrong-time" electricity generated by wind farms at night can be used to chill air to a cryogenic state at a distant location.

When demand increases, the liquid air can be warmed to drive a turbine.

Engineers say the process to produce "right-time" electricity can achieve an efficiency of up to 70%.

IMechE is holding a conference today to discuss new ideas on how using "cryo-power" can benefit the low-carbon economy.

The technology was originally developed by Peter Dearman, a garage inventor in Hertfordshire, to power vehicles.

A new firm, Highview Power Storage, was created to transfer Mr Dearman's technology to a system that can store energy to be used on the power grid.

The process, part-funded by the government, has now been trialled for two years at the back of a power station in Slough, Berkshire.

More than hot air The results have attracted the admiration of IMechE officials.

Mr Dearman uses his garage as a laboratory

"I get half a dozen people a week trying to persuade me they have a brilliant invention," head of energy Tim Fox told BBC News.

"In this case, it is a very clever application that really does look like a potential solution to a really great challenge that faces us as we increase the amount of intermittent power from renewables."

Dr Fox urged the government to provide incentives in its forthcoming electricity legislation for firms to store energy on a commercial scale with this and other technologies.

IMechE says the simplicity and elegance of the Highview process is appealing, especially as it addresses not just the problem of storage but also the separate problem of waste industrial heat.

The process follows a number of stages:

  1. "Wrong-time electricity" is used to take in air, remove the CO2 and water vapour, which would otherwise freeze solid
  2. the remaining air, mostly nitrogen, is chilled to -190C (-310F) and turns to liquid - this provides a compact storage medium that can later draw energy in the form of heat from the environment
  3. the liquid air is held in a giant vacuum flask until it is needed
  4. when demand for power rises, the liquid is warmed to ambient temperature. As it vapourises, the expanding gas drives a turbine to produce electricity - no combustion is involved

IMechE says this process is only 25% efficient but it is massively improved by co-siting the cryo-generator next to an industrial plant or power station producing low-grade heat that is currently vented and being released into the atmosphere.

The heat can be used to boost the thermal expansion of the liquid air.

More energy is saved by taking the waste cool air when the air has finished chilling, and passing it through three tanks containing gravel.

The gravel remains cool until it is needed to restart the air-chilling process.

Delivering durability

Highview believes that, produced at scale, their kits could be up to 70% efficient, and IMechE agrees this figure is realistic.

"Batteries can get 80% efficiency so this isn't as good in that respect," explains Dr Fox.

"But we do not have a battery industry in the UK and we do have plenty of respected engineers to produce a technology like this.

"What's more, it uses standard industrial components - which reduces commercial risk; it will last for decades and it can be fixed with a spanner."

In the future, it is expected that batteries currently used in electric cars may play a part in household energy storage.

But Richard Smith, head of energy strategy for National Grid, told BBC News that other sorts of storage would be increasingly important in coming decades and should be incentivised to commercial scale by government.

He said: "Storage is one of four tools we have to balance supply and demand, including thermal flexing (switching on and off gas-fired power stations); interconnections, and demand-side management. Ultimately it will be down to economics."

Mr Dearman, who also invented the MicroVent resuscitation device used in ambulances, told BBC News he was delighted at the success of his ideas.

He said he believed his liquid air engine would prevail against other storage technologies because it did not rely on potentially scarce materials for batteries. "I have been working on this off and on for close on 50 years," he told BBC News.

"I started when I was a teenager because I thought there wouldn't be enough raw materials in the world for everyone to have a car. There had to be a different way. Then somehow I came up with the idea of storing energy in cold.

"It's hard to put into words to see what's happening with my ideas today."

John Scott, from the Institution of Engineering and Technology (IET), added: "At present, pumped-hydro storage is the only practical bulk storage medium in the British grid.

"However, locations are very restricted," he told BBC News. "In the future, if new storage technologies can be deployed at a lower cost than alternatives, it would benefit the power system."

A spokesman for the Department of Energy and Climate Change (Decc) said it would shortly launch a scheme to incentivise innovation in energy storage. Other grants are available from Ofgem.

Follow Roger Harrabin on Twitter: @RogerHarrabin


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  • rate this

    Comment number 479.

    What all the fuss is about. Physics can quite easily identify ways of storing energy including heating or cooling gasses or many other ways of generating potential energy e.g. elevating weight or compressing springs. This individual may have developed a gas method but is it the most efficient method? It should be quite easy to compare with other methods before developing further.

  • rate this

    Comment number 478.

    Liquid Nitrogen has been used as refrigerant in the food industry for many years. Storing and controlling liquid nitrogen is a well known technology and should present few problems.
    This technology could also be used on the national grid not just on wind farm generation. The used of low grade heat in the process is a major step in improving the efficiency of the process.

  • rate this

    Comment number 477.

    #473. FisherOfTruth
    "Feed the green night time energy into the grid and power down the fossil fuel plants accordingly."

    Fossil fuel plants, such as coal or gas powered ones, run most efficiently when running at their rated capacity.

    Makes no sense to close them down. Enormous losses involved in starting them up.

    Does any wind make sense?
    Particularly when it needs to be backed up with Diesel...

  • rate this

    Comment number 476.

    @471: There is the loss on conversion from air to liquid, and then the loss on conversion from liquid to air, and then the loss in the turbines. Then the figure of 70% is a theoretical figure. So you'd get something like 60% * 60% * 80% = approx 25%.

    By storing heat from one stage and using it in the other, they get 70%, which is pretty amazing (to me, not being a thermodynamics expert).

  • rate this

    Comment number 475.

    I wonder if the "wrong-time" electricity, combined with other scientific techniques, can be as used efficiently to produce hydrogen fuel.

  • rate this

    Comment number 474.

    #462 Mike - you'd rather rely on the French or the Russians?

    You must really hate the Scots;-)

    #468 Angus Cleaver - because potential wind energy is much higher. Britain has amongst the highest wind power potential in Europe, on and off-shore. Its about using the resources available to you and minimising external exposure and exposure to depletion of non-renewable energy sources.

  • rate this

    Comment number 473.

    But wind farms don't produce enough energy to fuel the country at night on their own, so where's the point in storing the energy they produce?
    Feed the green night time energy into the grid and power down the fossil fuel plants accordinly.

  • rate this

    Comment number 472.


    There is of course the heat generated by compression to consider. This could be stored and used to assist the gasification.

  • rate this

    Comment number 471.

    463 Student

    Can you explain why the maximum efficiency is only 25%? Is the calculation not:

    efficiency ≤ 1 - 83/283 = 70%-ish

    Assuming the external temperature is around 10 degC?

    I'm not a scientist or an engineer, but I would like to know.

  • rate this

    Comment number 470.

    There is, for instance, a very well well
    researched proposal to convert it to conventional liquid fuel:
    Which will still need to be combusted to create energy thus creating excess CO2.

    You didn't think that through, did you?

  • rate this

    Comment number 469.

    55 Minutes ago
    It is just a scam.

    It's not just about efficiency , a process that is only 10% efficient but still economical given construction/operating costs and environmentally friendly is still worth doing

  • rate this

    Comment number 468.

    Overnight demand, according to the National Grid, at present is about 25GW. Wind is contributing 3GW at the most, so why on earth would anyone need to 'store' electricity from wind generation? Can you imagine wind producing in excess of 25GW?

  • rate this

    Comment number 467.

    It seems that there are more direct
    and more efficient ways to use
    excess electricity generated by wind turbines.

    There is, for instance, a very well well
    researched proposal to convert it to conventional liquid fuel:

    The efficiency is still not perfect,
    but it is much better than in
    thermal storage/recovery schemes.
    Why not try that first ?

  • rate this

    Comment number 466.

    If plans to power the country with wind, sun, fairy breath and baby laughter are to be viable then cheap, efficient energy storage is going to be extremely important.

    Then again theres always nuclear.

  • rate this

    Comment number 465.

    @458 Englishvote

    I think you're missing the fact that @444 Alex has converted from Kg to tonnes.

  • rate this

    Comment number 464.

    Liquid air is very safe as long as you don't come into contact with it. That said, heat gain is an issue - but the larger the system, the less of a problem this is. Then again, this system needs industrial heat to get the required efficiency and the only really big sources of this are thermal power stations.

  • rate this

    Comment number 463.

    Performance measure of a device that uses thermal energy can be easily calculated:


    For the proposed process the limit
    is 25%

  • rate this

    Comment number 462.


    The greatest advantage over hydro power is that we in England dont have to rely on the Scots so much.

  • rate this

    Comment number 461.


    No I haven't read every post on the board - sorry.

    And no - clearly it won't exacerbate global warming if CO2 is returned to the atmosphere - my point was that if this technology is used on a large scale then using it to remove some of the excess carbon from the atmosphere would be an added benefit.

    Why don't you think before trying to patronise?

  • rate this

    Comment number 460.

    32.Trout Mask Replica

    Given your latest moniker, I would have thought you could see the surreal nature of scientists demanding money try and change the weather. BTW, did you notice I defended you earlier when someone described you as a student?I am sure you have never been one.


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