Liquid air 'offers energy storage hope'

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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 459.

    It's easy to see who was bunking off their physics classes.

    Carnot was the bloke of note.

    Wake up at the back.

    Truth is coming to get you.

  • rate this

    Comment number 458.

    @444 Alex
    “calculation gives about 15kg/KWhr (about half that of Li-ion). That scales up to 360000 tons / Gwday”

    I have no idea where you get the 15kg to the KWhr, but you have left 3 0's off the tons, a KW is 10^3 watts, a GW is 10^9 watts.

    Your maths leaves something to be desired

  • rate this

    Comment number 457.

    A French guy called Guy Negre has built engines (e.g. to run vans) that runs on compressed air. Wouldn't this be a more efficient way of recycling the energy?

  • rate this

    Comment number 456.

    If a home owner purchases a Solar Array and all unused energy generated goes into the system, the system is not going to have such a great demand put onto it
    Think it thru!
    Enough homes & businesses with Solar Arrays or wind towers will reduce demands @ peak hours dramatically
    Your need for storage is reduced & passes as the sun rises, people sleep at night, well they party too
    But what the heck!

  • rate this

    Comment number 455.

    432.Trout Mask Replica
    40 Minutes ago
    "Sidney Monroe
    If AGW did not rely on guesswork one of the computer models would have made an accurate prediction by now"

    Since you demand that every prediction, even those with strong caveats and uncertainties, be met every time before you are satisfied.'

    Just one prediction coming true would be nice Mr Trout/Retain/Centre/Logic etc.

  • rate this

    Comment number 454.

    Superb, well done that man!

    Storage is key to unlocking renewable energy intermittency and this looks like a promising development. I had thought that, with sufficient development, hydrogen was the optimal solution - perhaps one day, hopefully in the not too distant future.

  • rate this

    Comment number 453.

    If I log on to 15 different bbc HYS accounts and mark my comments positively it may well look as though folk agree with what I say.

    It will not make one iota of difference to this scheme however.

    One way or another.

    Efficiency is efficiency is efficiency is

    And that is what matters.

    I hope these guys like their gravy.
    It wont last forever.
    The government is looking to educate engineers. Good

  • rate this

    Comment number 452.

    Besides - would YOU want a tank of liquid air at minus 200 degrees C in your basement ?
    Very dangerous - if there's a fire in your house it would be big BA-DA BOOM !
    Nearly all pubs in the UK now have these as standard to create the gas that goes into every pint served.

  • rate this

    Comment number 451.

    438. Wee-Scamp
    The amount of energy needed to cool the air has already been taken into account.
    Engineers have sometimes got things wrong but they have long experience with the machines used for this process and know what they are talking about. Problems will come when money-men try to get them to tweak things to 'reduce costs' and thereby make the scheme less efficient.

  • rate this

    Comment number 450.

    Liquid air storage, a sort of solution, but storage is a distraction.

    The main problems are baseload and on-demand provision. Even with like-for-like generation and storage, where every off-peak "green" kWh generated is stored for later use, intermittent renewables will never come close.

  • rate this

    Comment number 449.

    442 englishvote : Are you one of folks who deny global warming and think Oil and Gas pollution are good to breathe?
    More power to the nut jobs that want to preserve clean air and a pure aquifer! Right wing Extremists in U$A are all for fracking for gas and polluting our aquifer
    What a trade off!
    They are making billions now and will in the future when they sell the ordinary poor sods pure water!

  • rate this

    Comment number 448.

    re. #397.Typical_English_No8: "until you get the likes of America, China and India etc to cut their levels of pollution, you are rather, 'urinating head on into a very stiff breeze'..."

    True but show them a cost effective way to produce more power with less pollution and the idea sells itself, especially to industrial users. This technology could make a real difference.

  • rate this

    Comment number 447.

    I hope we would be left with enough air to maintain our breathing.....

  • rate this

    Comment number 446.

    @431 Mark.

    Read back through the thread - this has been discussed. You are going to tell us that this will exacerbate global warming aren't you.

  • rate this

    Comment number 445.

    It is just a scam.

    Although energy can be stored this
    way, most of it will be lost along the
    way.From basic thermodynamic principles any such scheme has
    limited efficiency. Even if the
    equipment was 100% free from
    friction and other such losses,
    fundamental limit for this particular
    process is approximately 25%,
    if you go from room temperature (300K) to liquid air temperature (78K), and back.

  • rate this

    Comment number 444.

    @277: Liquid air can store much more energy than compressed air. A quick calculation gives about 15kg/KWhr (about half that of Li-ion). That scales up to 360000 tons / GWday. Liquid air is very easy to store - a 100m diameter dome with a 1GWday capacity is quite possible.
    @207: You need to think of the liquid air as a fuel. Not as dense as oil, but no reason for it to run out.

  • Comment number 443.

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

  • rate this

    Comment number 442.

    Putting the line in the article about removing CO2 appears to be rather distracting for many.

    It is irrelevant because the quantities are tiny

    Once construction of the thousands of additional electricity pylons starts people ill realise just what a con “green” energy is, and once the lights start going out the taxpayer will start to get mad about all the lies

  • Comment number 441.

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

  • rate this

    Comment number 440.

    428. @Davidtrev You ARE missing something. These cooled air storage units ARE batteries!


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