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 279.


    Why bother to @ me unless you understand the process?. If you want a more exact explanation look at 173 I dont have enough characters to explain it all. The article does point out it MUST be near a viable heat source like a power station to make it efficient it doesnt store any heat! When it heats up it absorbs heat from the source both ambient heat and supplied by power station.

  • rate this

    Comment number 278.

    Not sure if this has already been mentioned but what sort of size are we talking about to be useful on a national grid scale? How long would it keep for? A day? a month? Lots of questions and not enough detail.

  • rate this

    Comment number 277.

    Neat idea but I've seen a similar idea while I worked in the energy industry then it was using wind farms to pump comressed air deep into the ground and let it out at very high pressure and temp to run turbines. Both good ideas but the cost will be so high companies won't go down this road, and anyway where is all the liquid air to be stored?, your going to need vast storage areas.

  • rate this

    Comment number 276.

    " Mayna
    I did/do not compare it with fuels, only hydro energy storage."

    If your concern is whether this has a material effect on the CO2 levels in the air then you can be assured that is does not.

    You don't have hot energy or cold energy.... just energy."

    Though entropy is related to the temperature of that energy and so limits the efficiency at which is can be exploited.

  • rate this

    Comment number 275.

    If this new technology significantly reduces reliance on fossil fuels, and provided it is scientifically proven that it does, then this is a good step in the right direction.

    Clean, reliable, green and low-cost is the way to go (but please come up with an alternative to get rid of those costly and unsightly wind turbines!)

  • rate this

    Comment number 274.

    There is a technical error in your article.
    You DON'T store coolness.
    The cool air is at a lower temp than the gravel, so the gravel gives up it's heat until the system is in equilibrium. Then you insulate the gravel so that the thermal flow from the environment to the gravel is extremely low.
    Go and have a look at the Laws of Thermodynamics !
    It's the 2nd basic Physics blunder seen here today !

  • rate this

    Comment number 273.

    @ 250. Mayna

    Your analogy is wrong. This process does not add co2 to the atmosphere - oxygen and nitrogen are temporarily removed - by definition it is carbon neutral.

  • rate this

    Comment number 272.

    @240 'WendyRainbow'
    Please don't be despondent. Yes, population growth is a problem, globally, but it doesn't make you less worthy, nor should it.

    I don't know from your post where you live, nor your circumstances - but if you feel so low call Samaritans 08457 909090 or go to

    Not judgemental, not political, not religious. Kind regards, coram.

  • rate this

    Comment number 271.

    10 Minutes ago
    I'm with the Danes and wind to H2 to methane here. As inefficient but better outcomes.

    We already have the means of storing and distributing hydrocarbons as gaseous and liquid fuels. So those synthetic fuels look very useful.

  • rate this

    Comment number 270.

    55. Andy Sanderson
    "Stores what? Coolness? That's not in GCSE Physics... in fact, it's not in Physics at all. Another sad contribution to the public ignorance of science."

    I need to back Andy up here. You cannot store "coolness". "Coolness" is the lowering of energy in a system by taking it away.

    You don't have hot energy or cold energy.... just energy.

  • rate this

    Comment number 269.

    Maybe I mis-read it, I thought this system doesn't need wind, it works by converting liquid to gas to turn the turbines?? I think it sounds goo to me, although, I'm no expert!

  • Comment number 268.

    This comment was removed because the moderators found it broke the house rules. Explain.

  • rate this

    Comment number 267.

    "Technically speaking, you are correct that while the air is liquefied overnight, IF the CO2 when frozen is released STRAIGHT back into the air, there will be an infinitesimal increase in the CO2 levels"

    So as I said, if used for LONG TERM storage ....

    263.Trout Mask Replica

    I did/do not compare it with fuels, only hydro energy storage.

  • rate this

    Comment number 266.

    NIMBY's object to wind farms supposedly because of this issue of intermittent power generation. Of course it's a ludicrous objection (I live in Scotland). One doesn't even need compressed air plants like the one discussed here. Surely pumping water from a low place to a high place and then using the water down-flow to drive turbines achieves much the same result. This is not rocket science.

  • rate this

    Comment number 265.

    Another possibility occurs to me as a means to store "wrong time" energy, which is analogous to the proven strategy of pumping water uphill, is to pump air underwater (especially at offshore wind turbine sites) and have it drive turbines as it resurfaces when energy is required. Not sure of the practicalities as you would need to contain the submerged air somehow.

  • rate this

    Comment number 264.

    Great idea.
    We pay 30% extra for our electricity, to subsidise covering half the country in hugely expensive wind turbines, that will never generate enough to recover the amount of energy needed to install them. Now we can cover the other half of the country, and store the electricity produced during the 50% of the time when the wind actually blows.
    If we hugely increase the subsidy we pay.

  • rate this

    Comment number 263.

    250. Mayna

    And compared to the 100Mtons of CO2 being released each day by burning fossil fuels and even the CO2 not being released by burning fuels to provide a similar output of electricity as through this method, this is a problem because......?

  • rate this

    Comment number 262.

    British brilliance at its best.
    If the government can support this then maybe the power suppliers can be effectively reigned in and forced to supply cheaper energy to the masses.
    With our weather predicted to get wilder as a result of global warming an effective storage process will even out the current ups and downs of our current supply issues.

  • rate this

    Comment number 261.

    Balanced, mixed approach to our energy demands. As our population grows, more people will make demands. those who have access will never give it up and those who aspire will always want it. We have lost our way with our two cars, foreign holidays and our disposable life style. I think the solution needs everyone's buy in and needs to be radical.

  • rate this

    Comment number 260.

    If we could make energy from our farts it wouldnt matter one bit because all the while we have crooks running our energy companies the price will keep going up, how many people will die of the cold this winter because their too scared to turn on the heating due to cost last year over 12000 people did just that, we need our govt to cap price hikes they do in France?


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