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CryoEnergy System uses liquid air to store energy


March 16, 2011

The CES pilot project in operation at Scotland's Slough Heat & Power plant (Photo: Highview Power Storage)

The CES pilot project in operation at Scotland's Slough Heat & Power plant (Photo: Highview Power Storage)

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Balancing demand for energy with timely production is a juggling act that is particularly relevant to renewable sources such as wind and solar. Because the wind isn't always blowing and the sun isn't always shining, the energy produced by these systems needs to be stored efficiently so it can be used when it's needed. While some scientists are looking into storing such energy by converting it to natural gas, Britain's Highview Power Storage has its own approach, which is already in use in a pilot project. In a nutshell, the company is storing excess energy as liquid air.

In Highview's CryoEnergy System (CES), excess energy is used to run refrigeration units which cool air down to a temperature of -196C (-320.8F), at which point it liquifies. The liquid air, also known as cryogen, can be stored in an insulated tank, at an ambient pressure of about 1 bar.

At higher-demand periods, when the direct output of existing energy sources can't meet the needs of the municipal power grid, the liquid air is released into a confined space. The liquid boils as soon as it is heated above -196C, so even room temperatures will superheat it, causing it to regasify and expand in volume by approximately 700 percent. From there, a steam engine effect comes into play, with the high-pressure gas spinning a turbine which in turn powers a generator.

When exposed to ambient air temperatures, the liquid air returns about 50 percent of the energy that went into creating it. If exposed to heated air, however, the phase change from liquid to gas is more intense, resulting in an efficiency of up to 70 percent. If a CES were to be installed at an existing facility where waste heat were already present, the system could use that heat to boost its own efficiency. Conversely, because the only by-product of the system is cold air, it could also be used to provide air conditioning, refrigeration, or even to create more liquid air.

Currently, one of the most common forms of large-scale energy storage is the pumped hydro method. In this system, excess energy is used to pump water from one body of water up to a reservoir at a higher elevation. When power is required, water is released from that reservoir through a dam, spinning turbines as it cascades back down. While that system is more energy-efficient than CES, it is also reportedly more expensive to build and operate, requires a mountainous topography, offers a much lower energy density, and the energy it stores isn't portable. Tanks of liquid air, on the other hand, can be loaded onto a truck and transported to where power is needed – assuming that the energy required to run the truck is less than the amount that is being delivered.

According to a study conducted by consulting firm Frost and Sullivan, the use of batteries for energy storage is inferior to CES, when all criteria are combined. While some types of batteries offer more energy efficiency, they cost about US$4,000 per kilowatt of generating capacity, while CES only costs a quarter of that amount.

A 300-kilowatt pilot demonstrator of the CryoEnergy System has been in use at Scotland's Slough Heat & Power plant for the past nine months, where it has been utilizing the plant's waste heat, and regularly exporting electricity to the national grid. So far, the air has been liquified off-site, but the next phase of the project will integrate a liquifier into the system. The company plans to have a 3.5-megawatt commercial-scale plant operational by late next year, with plans to increase its capacity to 8 to 10 megawatts by early 2014.

Via New Scientist

About the Author
Ben Coxworth An experienced freelance writer, videographer and television producer, Ben's interest in all forms of innovation is particularly fanatical when it comes to human-powered transportation, film-making gear, environmentally-friendly technologies and anything that's designed to go underwater. He lives in Edmonton, Alberta, where he spends a lot of time going over the handlebars of his mountain bike, hanging out in off-leash parks, and wishing the Pacific Ocean wasn't so far away. All articles by Ben Coxworth

Battery prices will come down drastically, plus they are convenient. Efficiency is paramount. Wastage is sin.

Also, why not a technology that HEATS something instead of cooling something? The power plants produce heat as a by-product and its free.


If this is possible then, this would be more better option rather than making a situation like Japan. We may spend more but it will keep us all and the nature safe.

Robert Thomas

The question is,is it easier to keep something hot, or cold? Molten salt is used with solar energy storage, but that must take a lot of energy to heat it. I think there might be too great an efficiency loss (50%) to make it worthwhile. I think it is wasteful for power stations to use cooling towers, with the (waste)heat being lost up the cooling towers as steam. There has got to be a better way.


The efficiency of the cryo-storage system could be improved by using the cold end of sterling cycle engines to heat the gas.

sidred - March 17, 2011 @ 10:20 am PDT

A less efficient system that you can afford to build is superior to to a more efficient system that you can not afford to build.

Robert Thomas - March 17, 2011 @ 06:49 am PDT

The situation in Japan is a record earthquake, (which the 40 year old reactors survived just fine), followed by a record Tsunami, (twice as high as the anticipated worst case scenario) that took down all the reactors support equipment through power loss. And still there has been only minor radiation releases. Modern nuclear reactors use convection currents to provide cooling. There are ten of thousands of people dead, and missing and everybody is freaking out about the nuclear power plant that has killed less than ten people, by exploding hydrogen not radiation.


Slowburn: You concisely gave one of the best quotes I\'ve seen all week on the current disaster, that should make us all think about how safe nuclear power is in its current modern state (vice our current coal-plants that are estimated to contribute to tens of thousands of deaths EVERY YEAR in the USA by the particles they release.)

People freak about the small possibility of death by radiation when the tsunami wiped out tens of thousands. Better to not live near the coast, than worry about living by a nuclear power plant! The ocean is more dangerous!

Matt Rings

well slowburn..it looks like your handle is appropriate, as now all 6 reactors including the fuel from the shut down reactors are burning..slowly..toward a meltdown..I hear airplane seats to Tokyo are going pretty cheap..perhaps you should give us a ringside report...


the 700% quoted for expansion of liquid air into gas is ridiculous. That\'s only 7 times the volume. My dive tank stores 120 cu ft of air in a tank with an internal volume of only a couple cu ft. And it\'s not liquified. It should be 700 times (70,000%) not 700%.

Also, what do they do with all the heat that comes off when compressing the air? There\'s a lot of heat given off (again that\'s why they sit dive tanks in a water bath when filling them). When the gas is expanded again, that energy is required back (which is why in that photo all the pipework is frozen over). So this thing will suck a lot of heat out of the area it\'s expanded back into. That energy isn\'t free.


@Adrien - they would be using the excess energy from the primary source (heat) to cool the air - eg: an Absorption Refrigerator. Your skuba tank, which is compressing the air, has the unwanted side-effect of acting like a different kind of refridgerator (a heat pump). PV=nRT.

In other words - take a look at the back of your caravan\'s fridge. Fire from the gas outside makes it cold inside.

Cool :-)

@windykites1 - Don\'t be so fast to claim Japan is under control! 8000 uSv/h is not my idea of \"minor\" (0.07 uSv/h is what my dosimeter normally reads!). Sending a cloud of radioactive fallout over 30 million people is probably not such a great idea. The mere fear of problems killed 50,000 unborn (abortion) babies after Chernobyl remember!

Bring on the pebble reactors, so nobody has to pay this high price for accidents again!


wavetop - Your anti-nuclear fear mongering has been noted. And dismissed by the rational.


The proponents of thorium-fueled reactors, particularly a variant known as LFTR, claim that type of reactor, which several passive safety features, is safer and far superior to pebble-bed types, and just about ever Gen IV uranium, solid-fuel reactor.

Nick Huggins
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