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The latest renewable energy: Liquid air

By | October 2, 2012, 3:52 AM PDT

A few years after asking "Why is there air?," Bill Cosby amused us with his Fat Albert shtick. Hey hey hey Bill, air can store energy.

The comedian Bill Cosby once asked, “Why is there air?” Today there’s a new answer - to store energy.

Air, that invisible ampleness all around us, could hold on to energy from wind turbines that spin at night when we don’t need the electricity, and then release it later, the BBC reports.

All you have to do is first turn the air into a liquid state, using technology adapted by a British company called Highview Power Storage.

Liquid air? Gulp! It might sound more suited for drowning, but it’s just the sort of thing that ironically could help assure us an easier time of future breathing by curbing CO2-induced global warming and all its choking effects.

Highview uses night time electricity generated by wind turbines to chill air down to -190 degrees C (-310 degrees F), at which point it becomes liquid nitrogen. (I assume the process could also store excess daytime solar energy, although the BBC article only discusses wind).

Store that liquid in a giant vacuum, heat it back into a gas some other time, and the rush of air will drive a turbine. Feel good that renewable energy, not dirty old coal, will power your coffee maker in the morning. Except possibly for one thing - some external energy source has to help warm things up, and that source might not be renewable.

Another concern: At the moment, the process is only 25 percent efficient according to the article. I assume that means that it delivers only 25 percent of the electricity that it takes to liquify the air in the first place. That’s better than nothing, but it obviously leaves room for improvement.

The Institution of Mechanical Engineers believes the process can hit 70 percent - not too far from the 80 percent delivered by batteries.

One technique that could help, according to IMechE: Locate the air chambers near industrial plants or conventional power stations, where waste heat will help warm the air. Note, though, that this probably relies on CO2-emitting fossil fuels powering those plants (until small nuclear reactors arrive to provide process heat, but that’s another story). Nevertheless, it is effectively helping to cut down on their environmental impact.

Another trick: Run surplus chilled air through gravel that relinquishes coolness to assist in subsequent air cooling.

You have to admire the imaginative engineering, all of which derives from the work of Britain’s Peter Dearman, who invented a liquid air engine to power vehicles, as you can see in this video of him and his cryo car:

Dearman believes that liquid air will trump other energy storage technologies because it does not rely on potentially scarce metals. Or, to paraphrase some other Brits - The Hollies - some time, all we’ll need is the air that we breathe.

Reader Advisory: Apologies for the wandering pop history today. From Bill Cosby to The Hollies. This story best read while wearing bell bottoms.

Photo: From Wikipedia, and not meant to imply any position by Mr. Cosby on liquid air or energy.

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Mark Halper

About Mark Halper

Mark Halper is a contributing editor for SmartPlanet.

Mark Halper

Mark Halper

Contributing Editor

Mark Halper has written for TIME, Fortune, Financial Times, the UK's Independent on Sunday, Forbes, New York Times, Wired, Variety and The Guardian. He is based in Bristol, U.K.

Follow him on Twitter.

Mark Halper

Mark Halper

Mark has no financial holdings in the companies he writes about. He occasionally travels at the expense of companies or their press relations agencies in order to report on a company or industry event related to it; Mark will prominently disclose this information when appropriate. This relationship will have no influence on his coverage. Companies he covers do not get to review columns in advance, or select or reject topics.

He writes for SmartPlanet and is not an employee of CBS.

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+1 Vote
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liquid air
Efficiency is not everything, pumped storage is for instance only 60% efficient. The forte of the liquid air storage is its capability to drive very cheap, reliable and compact engines, and if combined with fossil fuels, this power could be variable & admirable. So it could find its niche uses in peaking plants, harbor tugs, heavy cranes, floating docks, emergency pumps in nuke plants, fire truck pumps, etc., but in cars hardly. Its energy density and efficiency are too low, and its evaporation too fast.
Posted by praoss
2nd Oct
+1 Vote
+ -
Would it not be easier and more efficient...
to use that excess energy to turn water into steam and store the steam instead? Certain railroad operations used to use what they called a "fireless locomotive" where a coal-fired steam energy plant would charge a huge thermos bottle (oddball-looking boiler) on a locomotive and get from 8 to 10 hours of functional yard-switching operations out of that locomotive before it needed recharging. It wouldn't be that difficult to use a similar process to store steam created by those wind turbines' excess electricity and use it to drive more highly-efficient steam turbines during the morning surge and maybe even balance some of the summertime air conditioning load.
Posted by DWFields
2nd Oct
0 Votes
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An Answerable Question
@DWFields, your question is an answerable one--I just have not done the calculations. However, safety is also an issue. An equivalent amount of energy stored in liquid air (I do not like this phrase, see below) is probably safer than that stored in steam. A catastrophic release of liquid air will not be as dangerous as a similar release of steam or liquid CO2 for that matter.

Actually the energy is being removed from the liquid air and being deposited in the gaseous air at the compressing station--so there is already waste heat at the compressor site but maybe not as high in quality as that from an industrial site. Creating a colder heat sink for the engine is really all that is going on here.
Posted by EmmettRedd
2nd Oct
+1 Vote
+ -
Not really the best design
Those designs were mainly used in mines and factories where an open fire could cause a massive explosion. They weren't more efficient than standard steam engines. While they did store steam at a superheated temperature and pressure, most of the energy storage came from superheated water under pressure that was also in the "thermos bottle".

The most efficient heat engines derive their power from converting liquid to a gas (e.g., water into steam, or gasoline into gases from an explosive reaction). We've gotten pretty good at doing this as efficiently as possible. The problem with the liquid air design is that you have the added step of converting gas into a liquid first. You'll always have added inefficiencies from that no matter what.
Posted by zackers
2nd Oct
+2 Votes
+ -
A bit of an answer
Mark either doesn't quite understand what happens in the creation of liquid nitrogen or explain it badly. But what happens in the creation of liquid nitrogen is also part of the answer to your question about "fireless locomotives".

The boiling temperature of any liquid is directly proportional to the temperature but inversely proportional to the pressure. This creates some interesting phenomena. It's why you can use steam to cool a building. If we take water, inject it into a partial-vacuum such that the water's temperature is above the boiling point for that particular pressure, the H2O boils, and in the process, absorbs heat. When we then return the H2O to "room temperature and pressure" it condenses, thus releasing its absorbed heat. This is known as steam refrigeration.

Fireless steam locomotives place the water in a closed container, and then super-heat it. By reducing the pressure within the container, the water is allowed to boil, thus turning it into steam. The problem is, you're dealing with a super-heated material under high pressure.

Using liquid nitrogen means compressing the air. But as you compress the air, it loses its capacity to store heat and thus releases heat. So you carry off the heat to use somewhere else. Once the nitrogen is compressed until it is a liquid, and the excess heat has been removed, you then run into the problem of storing it since if it absorbs heat, it will boil away. Luckily, Liquid Nitrogen is fairly easy to store within a vacuum-walled thermos bottle without it being under high pressure. So while you use high pressure to make it, you don't need high pressure to store it. This makes it a safer storage medium.
Posted by mheartwood
2nd Oct
0 Votes
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Export
This would be best produced in cold countries, where the heat removed from the air could be used to warm houses, then the liquid air could be exported and used in hot countries that already have the heat needed to release the air, in the air. Also, it could be used to cool down hospitals etc. in Africa and similar places. "Liquid-air" pipes could run from the polar regions to the equator, and some sort of heatpipes could return heat in the form of hot water.
Posted by Dukhalion
2nd Oct
0 Votes
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pumped storage efficiency
In response to praoss in Liquid Air, pumped storage is not 60% efficient. Older plants are 65-80% efficient. New plants are considered to be 80% efficient.
Posted by Grids1
2nd Oct
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