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 539.

    - not that water pumps need exactly 50Hz either ! The waste is expecting synchronous 50Hz mains that can be pooled in transmission. We have lost sight of living by nature. The only way to couple wind power to our ego, is buffer it by some intermediate flexibility. The machine must extract power over a range of wind speeds. Yet we stop wind turbines if they are too slow or too fast to get 50Hz !

  • rate this

    Comment number 538.

    You are still missing the point ! This is storage AFTER we have wasted most of the wind power ! We spill enormous power to get a 50Hz sine wave for transmission. Past millers adjusted their product to suit the wind; grinding different animal feed or bread flour. We ignore the speed, and waste it. Pumped storage must speed variable, done at the windmill, not 200 miles away via 50Hz electricity.

  • rate this

    Comment number 537.


    Or an over populated one.

    What ever happened to compressed air powered vehicles ?

  • rate this

    Comment number 536.

    Does anyone know how this compares to pumping water to a large
    container at a great height? That is technology that has been around
    for years and it works quite well. I visited such a setup in Wales in
    the early 1980's.

  • rate this

    Comment number 535.

    Given that we started this year with a hosepipe ban and are ending it with floods, we seem to have plenty of water but insufficient storage - why not build more resevoirs and use them to store the energy from the windfarms.

  • rate this

    Comment number 534.

    "313. steven
    Wind turbines should be built at sea, round an artificial lagoon; they pump water. ... The electricity is generated when the water is let out through a generator. That's the way to use wind power !..."

    That would definitely be the best way to do it, but protecting such lagoons from tidal and storm damage would be the pinch point.

  • rate this

    Comment number 533.

    Both the electricity from the wind farms and the heat from the power station would otherwise go to waste.
    This is energy which would otherwise be discarded, and therefore costs very little in economic terms. The cost is in the build and operation of the liquid air plant and its associated generator. If that is economic at whatever efficiency it achieves, that is sufficient.

  • rate this

    Comment number 532.

    Solar panels on every house provided free from elecricity supplier, mini wind turbine on every roof, blow the cost, use free energy and use other less. Birds dropping from the skies, whales committing suicide, radiated tuna, bad crops due to insecticide losing natures battle, fukushima, chernobyl. We need to alter things now not later or drip drip drip. You cannot survive on a dead planet.

  • rate this

    Comment number 531.

    A dose of reality:

    Energy in watt-hours per kilogram of fuel (W-hr/kg):

    liquid nitrogen 100
    lithium-ion battery 250
    petrol 11000

    To produce liquid nitrogen requires 500 W-hr/kg.

  • rate this

    Comment number 530.

    This work may not be as original as is being reported. In 1998 C. Knowlen, A.T. Mattick, A.P. Bruckner and A. Hertzberg published a paper entitled "High Efficiency Energy Conversion Systems for Liquid Nitrogen Automobiles". Very similar.

  • rate this

    Comment number 529.

    This would be great in hot climates as the wast cold air can be used for air conditioning

  • rate this

    Comment number 528.

    Most energy storage systems sadly aren't profitable in a liberal energy market. A large availability of storage in the grid plus demand-side management will eradicate the cost advantage of off-peak electricity. Adding the costs of the electricity "consumed" by the storage due to

  • rate this

    Comment number 527.


    So, he wants to find a way to make it
    work. By the time when oil runs out..
    Hes got plenty time then

    We need some cheap storage solution now to help offset the expense of what has been spent.
    Germany with all their wind power could do with it also because they're having to build 23 coal & gas power stations as their 'renewables' are proving unreliable & expensive.

  • rate this

    Comment number 526.


    Precisely -- and there are people
    who already figured out most of the
    technological details to make it work.
    Look up "Doty Energy".

    According to the analysis, making
    liquid fuel using wind energy can be
    55% efficient.

    Making liquid nitrogen has theoretical
    maximum of being 36% efficient, in
    practice less than half of that.

  • rate this

    Comment number 525.

    Absolute tosh, a bit like perpetual motion - engy out does not exceed energy in - EVER

  • rate this

    Comment number 524.


    The beauty of this proposal is deceptive.

    Why should we pay for research
    and development of a system
    that will be only 10% efficient
    (see the linked article)
    in practice, when you would
    have chosen something that
    is closer to 50% efficient,
    if all the factors were carefully considered.

  • rate this

    Comment number 523.

    509 tothepoint
    Vertical rotating wind turbines, land under can be wilderness full of wildlife rather than manicured lawns.
    Combine this with water electrolysis, use some of the hydrogen generated to combine with the carbon dioxide to produce fuel gas and the rest to recombine in fuel cells. What would YOU do with the spare oxygen?

  • rate this

    Comment number 522.

    Few commentators here get the beauty & simplicity of this - off on irrelevant tangents. But some do. Efficiency is not an issue when the energy stored would otherwise be wasted or is very cheap off peak baseload. Simple energy storage near to users is the key to renewable & economical power. Powerline distribution to the storage is already there. Hydrogen has failed.This is really something.Bravo!

  • rate this

    Comment number 521.

    518 Cariboo : Plains Indians lived in Tipi's
    Wood was in abundance and it was a really hard life way back in the 1700's
    Now a days they battle with alcohol and the US government
    Lakota Oglala Sioux are trying to fight back and want to get wind farms on the plains
    I personally wish them the best as their plight is very close to my heart thru relations
    U$ Congress have blocked everything for 2 years

  • rate this

    Comment number 520.

    What idiot coined the phrase "wrong time electricity" for off peak electricity. Do we really need hype if this is a good system?


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