The Dearman Engine: Making Intermittent Generation Viable?

Posted: May 13, 2015 by tallbloke in innovation
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Claims of up to 70% efficiency have been made for converting ‘wrong time’ electricity produced by intermittent generators such as wind turbines to ‘right time’ electricity supplied onto the grid. The proposed storage medium is liquid air (with co2 and water vapour first removed. This -190C medium is used to drive a piston engine without combustion, and waste heat is re-used.


The BBC’s Roger Harrabin mis-reports this engine as a ‘turbine’ in this report:

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%.

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.

Full story


Dearman’s website page concerning the engine is here.

I wonder how much more efficient this engine is than a stirling engine using liquid air to create the heat differential.

  1. Of course the thermodynamic efficiency is low. Think Carnot.

    Those who fall for the 70% advertised are ignorant of Engineering basics.

  2. tallbloke says:

    Bernd: Premise for 70% instead of 25% seems to be dependent on cryo plant being built right next to waste heat source from another industry. So some scavenging from outside the carnot cycle would seem to be implied.

  3. To produce liquid O2 or liquid N2 is very expense and to waste the gas after the CO2 and H2O have been removed is plain stupid. It would be far better to extract CSG or shale gas and liquify that as done in US, and use that for continuous energy production, except the LNG plants cost multi-billions. Producing LNG, liquid O2 and N2 is chemical engineering, maybe these supposed mechanical engineers do not know about costs. Of course no socialist (who seem to be inhabiting all parts of academia) understands costs and economics. Plant cost estimation was an important part of my engineering studies. Most engineers in private industry have to understand capital costs and management cost control.

  4. Steve Crook says:

    What I don’t understand is what the 70% efficiency comes from. 70% across the whole cycle of compress, store, decompress and generate? Or just from the decompression and generation of what’s stored?

    Also, just what sort of volume of storage of liquefied gas are we talking about if we store enough for 10GWh of generation?

  5. oldbrew says:

    ‘the liquid air is held in a giant vacuum flask until it is needed’

    How ‘giant’ is that going to have to be, in order to be any use to entire countries?

  6. tallbloke says: May 13, 2015 at 10:58 am

    “Bernd: Premise for 70% instead of 25% seems to be dependent on cryo plant being built right next to waste heat source from another industry. So some scavenging from outside the carnot cycle would seem to be implied.”

    Current estimates for the “coal” storage of “insolation”, then modern conversion back to some useful power is 2%. This complete nonsense must be less than 0.02% max. How do we get the trees to produce more “coal”? What a wonderful way of reducing atmospheric CO2, until no more trees! 🙂

  7. tchannon says:

    An old idea, fallen many times, keeps resurfacing.

    If you compress the air with all the heat generated and keep all the heat the process would indeed offer reasonable overall goodness.

    Unfortunately the competition is unhelpfully good. Pumped storage for example can in large size do 0.9 x 0.9, 80%, anything good has to be large, including very very large for cost reasons.

    I happen to be well up on the subject, lets dig out a few things.

    [edit, oops, WordPress put it inline, ]

    “The system was used in England on the Wantage Tramway but did not find favour there because the compressor plant used more than four times as much coal as a steam locomotive.” This is fairly well documented. (twice I have worked in the Wantage area)

    And now consider that steam locomotives are horribly inefficient thermodynamically!

    The adding back in of heat is barely able to keep the expander frost free, let alone make up for the lost energy during the compression process.

    The bottom line is the lack of discussion of the overarching problem, perhaps ultimately well illuminated by the rejection of an infamous but accurate phrase “too cheap to meter”. This is about the protestant ethos of parsimony, thinking tiny and too small. If there is a need to electrify that does mean everything, which in turn means 100x or more electricity generation than the entire system today. Merely supplanting current generation capacity is a pointless joke.

  8. michael hart says:

    If it is credible then the likes of Praxair and BOC will presumably take it up first. But as others point out, storing enough liquid air to power a whole country for days or weeks in the middle of winter is a different proposition.

    And it has to be next to someone who is producing spare heat. A nuclear power station sounds about right.

  9. Graeme No.3 says:

    Liquifying air is a standard industrial process, used to produce EITHER liquid oxygen or nitrogen as the main product. They are CONTINUOUS processes. Once you’ve ‘boiled off’ the nitrogen you can easily re-liquify it in another additional cryogenic plant. Very large plants can produce 50-60,000 tonnes a day. And yes, they do store liquid gas.

    Nitrogen boils at -196℃ v oxygen at -183℃, so I wonder how much attention was paid to the idea by the vague description of around -190℃. And when they make up their mind what the working fluid is going to be, they might consider if the cryogenic plant could supply waste heat.

    Handling either liquid gas is hazardous, but nitrogen at least doesn’t fuel fires. Nitrogen is usually cheaper as well. The cost of these liquid gases is STRONGLY dependent on the cost of electricity, so encouraging lots of more expensive wind energy isn’t going to help the economics, and what about the backup for the continuous liquid gas producers?

    All in all, this sounds like a typical “green” or BCBC** process. Send more money now.

    **Bloody Clever But Costly.

  10. AlecM says:

    Isentropic compression and expansion is standard in these technologies.

    It’s just too bloody expensive……

  11. Fanakapan says:

    Going by the informed input above, this’ll be one to file with that Musk charlatan’s home battery mallarky ?

    But hey, it’ll make a lot of ‘Middle England’ BBC viewers have a cuddly feeling for 30 seconds, so from Harabins position its a Win 🙂

  12. catweazle666 says:

    No chance.

  13. p.g.sharrow says:

    Is it do-able? Well, yeah sort of. Would an intelligent person do it with his own money? H_E_LL NO!

    If the electric energy was free and you had a Fueled and operating thermal plant next door that would provide free heat energy during the energy reclaim cycle, then this might make sense to a politician or bureaucrat. Then this is an OPM user’s dream come true. pg

  14. tom0mason says:

    A French company called MDI had a similar idea for vehicle engines. Their idea was solar and wind powered fill-up stations would supply the electricity to run air compressors. These compressors would pre-fill cylinders that the motorist exchanged when more ‘fuel’ was needed leaving the empty to be filled by the sustainably green power plant. 🙂
    For some reason they could never get enough investors excited enough to stump up more money required to help iron-out the wrinkles in the technology.
    Now the whole idea has been ‘parked’ in a technology warehouse in Luxembourg

    Yep, another “green or BCBC process” as Graeme No.3 says.

  15. Konrad. says:

    This concept appears like a fools errand. The low efficiency and engineering difficulty of cryogenic liquids make this idea un-viable. Wind turbines and photovoltaic panels are inefficient to start with, and storage systems, while a step in the right direction, can never make the current technology viable for baseload power.

    There is however a way. Sunoba came close. Noel Barton, the founder, may have contributed here (IFRC) around the time Willis et. al. were smearing the Makarieva 2010 discussion paper. (my first empirical climate experiments upheld Makarieva’s claims).

    Barton’s design involved a condensation engine working in a similar manner to an old Newcomen atmospheric engine. Warm saturated air was drawn into a large diameter cylinder, then crash cooled with an ultra fine spray of cold water, driving the piston. The moist air was to be generated from solar pebble bed storage.

    An accidental discovery has led me to recently work on a similar design, with double the potential power of Barton’s and with higher speed of working gas temperate change. The up-shot of this is that it may indeed be possible to power the average home with just two standard solar hot water units, with the tanks acting as “batteries”.

    Solar hot water is about the only solar system with any real efficiency and effective energy storage. Conversion to electricity is a technology problem, not a science problem. The energy is easily collected and stored, but what is needed is a way to utilise what has formerly been referred to as “low grade heat”. It’s not the heat that is lowgrade, but our technology. Converting water to steam requires far more energy than causing water to evaporate into air. Barton realised that the same 1:1600 expansion of the water molecules still occurs in the lower temperature process.

    Ultimately what is going to be a better home solution, photovoltaic cells converting only 15% of visible light to electricity and expensive and dangerous lithium-ion storage? Or solar thermal collectors with black nickel selective surface and hot water storage in vacuum insulated tanks?

    I am a climate sceptic who knows full well that radiative gases cool our atmosphere, which in turn cools our solar heated oceans. CO2 emissions pose no threat whatsoever. However, due to the lessons learnt from the CO2 hoax, there are now reasons to look at alternative energy, especially for the individual citizen. The key to our modern civilisation is energy. Those seeking to control, subjugate and oppress will always strike here. What better end to the Fabian “long march through the institutions” than a bunch of sorry socialists in control of institutions that in turn control…nothing 😉

  16. steverichards1984 says:

    1) The linked article is from 2012!
    2) “the heat exchange fluid is reclaimed, reheated and reused, while the nitrogen or air is released back to the atmosphere.”: reheated? where is the energy for this ‘reheating’ coming from?
    3) Liquefying nitrogen (or any gas) is very expensive.
    4) Might as well just compress air with windmill power and use to power compressed air powered electrical generators.
    5) I can not see the ‘gain’ of cooling in this case….

  17. oldbrew says:

    French car maker Peugeot is dabbling in compressed air ‘energy storage’. Its prototypes can’t be plugged in for a recharge yet though.

    [image credit: Gizmag]

  18. manicbeancounter says:

    I look at the issue from an accountant’s viewpoint. Suppose the system is 70% efficient with utilizing the waste heat. The unit cost of electricity is going to be nearly 50% dearer than if the wind energy was directed straight into the grid. Then there are losses in cooling the air. Then there is the capital cost of this system. You are already looking at doubling the unit cost of electricity from wind turbines. Electricity from offshore wind turbines is already three times the cost of that from gas or coal-fired power stations.

  19. E.M.Smith says:

    Would it not be easier to use a fluid with more tractable temperatures? Propane or Freon-12 for example? And closed cycle, not throwing away the air after you’ve cleaned it.

    It also seems to need some kind of large heat storage system so that when you have made all the cold liquid the waste heat can be put in rocks or a eutectic salt bed, then you get that heat back during the expansion / vaporization stage via a liquid pre-heat.

    So once you are all done it’s going to be gigantic, and likely still not very efficient… but it could work… just not very economically…

  20. Konrad says:

    “double the potential power of Barton’s and with higher speed of working gas temperate change.”

    Not even a nibble? Seems Talkshop is losing its edge…

    Are Willis’ Warmulonians at WUWT going to win?

  21. Just build very large flywheels to store the energy generated so when the sun goes down or the wind don’t blow you can use the motor that powered the flywheel to generate DC and with a big inverter convert it back to the grid. Anyone care to work out the maths required? Best built deep in the earth in case an failure or inbalance tries to make the flywheel literally fly and cause damage.

    See wikipedia