Compressed Air Energy Storage: Renewable Energy

Compressed Air Energy Storage: Renewable Energy
Compressors use off-peak electricity to fill the cavern with compressed air. For peak demand, the compressed air is withdrawn from the cavern and used to power a wind turbine. Credit: Ridge Energy Storage & Grid Services LP

( -- Wind-power turbines have played an important step in renewable energy but now the future of wind power may be underground. By using compressed-air energy storage plants, air is pumped into large underground formations where it can be used later to deliver a large amount of energy that it received.

Electricity is cheapest in the middle of the night and by running air compressors, air can be pumped into a cavern or vessel at 750 psi. In the daytime, when the price of electricity is expensive, the compressed air is preheated with the heat generated and stored during compression and then used to help power a turbine.

Compressed Air Energy Storage: Renewable Energy
Compressed air is stored in a vessel during off-peak hours and released during peak hours to power wind turbines.

CAES (compressed air ) is relatively low efficiency and prices out to about $1000 per kilowatt of storage as compared to about $3000 per kilowatt for lead acid battery storage. These estimates are according to EPRI (Electric Power Research Institute).

There are currently a few CAES projects underway that are slated for government funding:

• New York State Electric and Gas is currently working on a CAES project that involves pumping into a salt cavern in upstate New York
• Pacific Gas and Electric is looking at a 300MW CAES project in Kern County

EPRI has determined that up to 80 percent of the US has geology suitable for CAES. EPRI has established that a single 300MW CAES plant would require about 22 million cubic feet of storage space; this storage space would yield eight hours of electricity.

Compressed Air Energy Storage: Renewable Energy
Regions with geology favorable for CAES and class 4+ winds are superimposed to indicate ideal CAES plant locations. Credit: Princeton University

From the above map it can be seen that hundreds of 300 megawatt CAES plants can be constructed across the US. This is relatively inexpensive and can turn intermittent like wind into more reliable distribution.

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Mar 17, 2010
This is old news! The idea of storing compressed air in underground caverns for use as a battery was discussed in depth last year in other resources. This seems to contain more advertising and less cutting edge development.

Mar 17, 2010
ok, how about a fat pipeline to offshore windfarms instead of powerlines and onsite converters, the long pipeline wopuld both serve as transporter and as buffer battery for power storage, a converter station could be based onshore to make electricity from the compressed air.

Mar 17, 2010
works well until the utilities allow the generating infrastructure to deteriorate, as they have for the last 50 years. 50 years ago the U.S. home delivery standard was 125V/250V, today it is 108V/215V. Your 50 year old coffee pot may not boil water today.

We don't need compressed air. We need NEW generating capacity and lots of it.

Mar 17, 2010
I have worked many years with compressed air systems and have grown to dislike them. They are nasty and maintenance intensive, especially large systems. To work properly the air must be dried before it is stored, which takes a lot of energy, and lubricant must be added to it before it is used. The extracted moisture stinks like s**t and is nasty. If lubricant isn't added to it when the air is used valves and such seize up quickly, and of course it is difficult to contain the oily air and clean it after it is used. With pneumatics the devil is in the details.

Mar 17, 2010
.... 50 years ago the U.S. home delivery standard was 125V/250V, today it is 108V/215V. ....

As a licensed electrician I believe your numbers are wrong. What is your source? 120/240 is more like it as far as my experience and research shows. My #2 key is sticky.

Mar 17, 2010
Flywheel storage is the ticket! Modern flywheels offer almost frictionless magnetic bearings,and run in a vacuum chamber to minimize losses.Compared to batteries,they offer unlimited charge/discharge cycles.

Mar 18, 2010
50 years ago the U.S. home delivery standard was 125V/250V, today it is 108V/215V. Your 50 year old coffee pot may not boil water today.

I think you may be confused by 2 phase vs. 3 phase power. With two-phase power, the phases are at 90 degrees to each other, and distribution typically uses 3 wires. Typically a house is connected to a single center-tapped phase, giving 120 and 240 volts. In a three-phase system delta is used for transmission (two wires with the third phase being ground). This is converted to Y (or if you prefer wye) to go to the house or factory. In theory you now have three phases (and wires) each 120 volts with respect to ground, and 208 volts between phases. This is used to power, in most houses, the dryer, an electric stove, perhaps a water pump, and some air conditioners. (I hope your house doesn't still use electric heat.)

Notice though, what happens if you have poor grounding. The ground drifts to between the two phases used for the dryer.

Mar 18, 2010
The same situation can occur if the load on one of the step down transformers (usually on poles in big cans) has an unbalanced load. This is your house and several of your neighbors. The phases shift out of a perfect Y, and two of the 208 volt supplies will drift up, and one will be lower. The same thing can happen with an imbalance between the phases and ground. One phase will drop, and the others will increase. (In theory the opposite can happen as well, but I have never seen it.)

What can you do to fix this? If you understand it, re-balancing the load in your house by moving wires around in the main power distribution panel can fix it. If you are not an Electrical Power Engineer (a lot of EEs today never take courses in power distribution) or a competent electrician, hire someone to do it. Don't buy any snake oil, AKA phase shifting capacitors, or the like. For most homes, moving an air conditioner to a different circuit is all it takes.

Mar 18, 2010
Ignore all the above if you live in California, and tell your politicians that not allowing new power plants to be built in the state is crazy. All the major urban areas need (more) power plants nearby. If you are drawing power from a long distance away, any shift in load sets the power grid dancing like a conga line.

It doesn't matter whether the plants are coal, oil, hydroelectric, nuclear, etc., as long as they put a lot of rotating generator mass near where the load is changing rapidly. Good electric companies have such generators idling on line as peak periods approach. This way they don't have to be spun up as demand rises, but it also means that there is more inertial mass on the line and close to where it is needed.

Mar 18, 2010
In order to achieve anything like say 80% to 90% return of energy invested into CA storage, the air taken out of storage must come out at the same temperature it went in.

It is worse than that. You need to continuously adjust the compression ratio to match the pressure in the storage volume. It can be done, but it adds expense to the system.

However, if you can store the air deep enough underground, the air will be heated by the earth. Add water, as in a salt dome, and you can have a (relatively) constant pressure system. So CAES systems using salt domes where oil has been extracted is not that unreasonable.

If the salt dome is three or four miles underground, and if it hasn't been too compromised by multiple wells for secondary and tertiary extraction, the system would work. The air would be kept hot by the ground.

However, given all of the above, it is probably easier to build a geothermal energy system which is a net energy producer.

Mar 18, 2010
lengould100: "the energy losses in compressed air storage due to cooling of the gas in the storage container"

With the underground scenarios, surely it would be the case that to start with the surrounding rock, and ground water I suppose, would certainly absorb heat from the compressed air. In time though the rock would reach a much higher ambient temperature and thus reduce that kind of energy loss. The water would heat up also which certainly could cause relatively slow convection through porous rock,a regular but slow loss of heat.
As this is meant to be a way of storing off peak energy so as to spread the load better across the daily cycle, each implementation would have to be looked at on its particular merits. In some places with the right rock formations at the right distances from power plants and consumers it may work very well.

Mar 20, 2010
No, underground CA is crap- this is a transparent effort by the petro/mining industries to coopt energy production, at very litle or no cost to themselves, and to maintain the stranglehold on energy consumers that they have profitably enjoyed for so long.
Think about it- who owns the sites they propose to use? Who will fund the projects? My guess is a large taxpayer subsidy, or direct rate hikes to utility customers. And of course- let's not forget how profitable maintenance of an inefficient and troublle-prone technology will be(think of how corrosive salt/wet air is, and compression/decompression cycle effects geologically, on the storage structures themselves), plus the"dirtyness" that RobertKLR pointed out, earlier.
This is the proverbial "pig in a poke" boondoggle, and the seller is EXXON/SHELL/CHEVRON/BP or one of their shell corporations.

I'm with Newbeak- FLYWHEEL ALL THE WAY!!!!

Mar 22, 2010
...Compared to batteries,they offer unlimited charge/discharge cycles...

What a dumb statement "compared to batteries" is a qualifier or limiter so offering unlimited charge cycles is impossible.

Besides its risky to say that anything is limitless.

Though what you were trying to say is spot on, fly wheels were a good idea and they've gotten better.

Mar 22, 2010
Damn, I should have made a crack about him working for a cell phone company.


Apr 12, 2010
Compressed air is viable, though not exactly in it's current form. Efficiency is less of an issue if the source is natural, wave or wind direct to compressed air works, particularly in a marine or nature sensitive environment.

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