Cheaper Energy From Caverns of Compressed Air

An anonymous reader writes "By using the Earth's vast underground caverns to store compressed air generated by wind farms at night, several U.S. municipalities will be 'going green' by using that stored energy to generate daytime electricity on the cheap. Engineers at a National Lab think compressed air stored in underground caverns could cut in half the cost of electricity."

Comments

vast?

[Ydna]

Earth's vast underground caverns? Oh please. If scientists actually tried doing this, it would surely bring about the end of life as we know it. The atmosphere would all be sucked up into these vast caverns leaving nothing but a vast vacuum on the surface. No, thank you!

Re:vast?

[w0mprat]

Your right, such a project would produce unacceptable levels of vacuum emissions into earths atmosphere. But this could be a good thing!: Production of Vacuum tubes and Cathode Ray Tubes in the 20th century used up all the easily available vacuum on earth (mined from the air which contained precious little vacuum! - bringing it down from space is not cost-effective!) humanity had to make do with the transistor and now we have to change to LCD screens since CRTs are no longer profitable to manufacture. But this could change things!

Re:vast?

[srjh]

You'll also need to purify the dirty vacuum that is present in the earth's atmosphere.

I suggest a vacuum cleaner for the task. (ducks)

Re:vast?

[PHPfanboy]

And this is why I have applied for a job at NASA. Think of all the vacuum we could mine from space!!! (Space is also very big but we'll make sure we get mines near to earth, to reduce our transport costs and make it cost effective)

We'll make a fortune selling vacuum to store in caves and then once we've sold to local authorities and energy companies we can sell to homeowners "A Vacuum for Every Yard" and then as the market becomes educated we can crack the enterprise and SMB market with "A Vacuum on every Desktop".

P.S.
I first got the inspiration for this awesome business opportunity idea from the documentary movie "Spaceballs".

Re:vast?

[TropicalCoder]

If we could find a way to compress the vacuum to a tiny fraction of its normal size, we could put it in little containers to power a vacuum cleaner. Imagine then - a "green" vacuum cleaner that runs on cans of this compressed vacuum instead of electricity! Instead of plugging in your vacuum cleaner, you just stick in a new can of highly compressed vacuum before you begin to clean the house.

How Efficient is It?

[TheStonepedo]

How far are the turbines from the caves? What happens if the wind that should be generating electricity for the compressors takes the day off and chooses to make an unfashionably late arrival? How much of a boost do the turbines get from the compressed air?
I'd think with enough losses along the way (steps up/down in voltage at transformers to transmit the power to the compressors, mechanical inefficiencies of the compressors, dependence of the turbines' optimum performance on this assistance) the project, while novel, could take a while to pay for itself. I'm not suggesting that bleeding-edge science should be economically feasible - that should come after the science is established - but that efficiency should be priority number one so that the technology can become competitive with other ways to store potential energy.

Re:How Efficient is It?

[tirerim]

I think they're mainly suggesting that it would be more efficient than storing the same energy in ordinary chemical batteries, which is the current method for storing energy from natural sources for times of higher demand (or lower production, in the case of solar). Presumably their calculations are based on minimizing the inefficiencies for both batteries and compressed air.

Re:How Efficient is It?

[Free the Cowards]

What happens if the wind that should be generating electricity for the compressors takes the day off and chooses to make an unfashionably late arrival?

You draw power from the grid, which you'll still be connected to.

Re:How Efficient is It?

[Rakishi]

The current method as I understand it for large scale energy storage is water. Specifically http://en.wikipedia.org/wiki/Pumped_storage

Compressed air probably less efficient but potentially cheaper to implement.

Re:How Efficient is It?

[WalksOnDirt]

How Efficient is It?

If you just throw away the heat generated during the compression, which I think is what is done in current large installations, I have read that you can get about 50% efficiency. The fact that natural gas is used in conjunction with the compressed air to regenerate the stored power confuses the issue, which leads to much higher efficiencies sometimes being claimed.

Here they are proposing to capture the compression heat and use it (with an "adiabatic generator"), which should help the efficiency. I'm a bit surprised the energy savings are worth enough to cover the capital costs of tapping such a low grade heat source, especially since this is also excess energy that will also need to be stored for later.

Re:How Efficient is It?

[kesuki]

you have a lot of questions but here is the point.

at night time the wind dies down to the point where wind turbines generate 0 power. the whole point is that they can compress air in existing underground caves, near municipal wind farms, to run them after dark.

I'm worried about long term side effects, 1200 PSI is a lot of potential energy, and cave systems, even an airtight system as this must be, are underground and usually there are things above it, in this case, prime iowa farmland. if the cave blows a gasket, you probably don't lose much, unless it happens to take the hill the windmill was on with it.

worse still, if you take down a farmhouse loaded full of farmers and get sued.. yeah the risk is low, and it saves using coal... oh and BTW because the power comes from the grid, the wind farm can be in one place, the cave system turbines in another location... (eg: using the same turbines to fill the caves as to create power at night)

but still, I'd feel safer with a atomic power plant in my backyard than a giant cave system being used to compress and store air to make power at night time.

Re:How Efficient is It?

[dbIII]

How Efficient is It?

Not very. The point however is to even out the load and fill the peaks, it's just another form of pump storage I suppose for places where you can't just conveniently pump water uphill. Despite the nuke lobby cry that it is all about base load the real problems are the peaks. With base load generation you have a whole lot of power being generated at night that isn't being used by anything and what is being used is lighting which mucks up the power factor. Running great big motors (like pumps) at night or resistance heating is what is usually done.

To sum up - a lot of energy is wasted but you get to fill the peaks without needing base load generation capacity equal to peak load requirements.

Sometimes wasting the energy is not a big deal. The ideal centuries old application for a windmill is to move enough water into a tank over the course of a week or two for use over the next week or two. With a long enough timeframe in the design it really doesn't matter if you have a few windless days or for solar a sudden cold snap. Compressed air however is a very inefficient way to store energy.

Re:How Efficient is It?

[Simon Brooke]

I think they're mainly suggesting that it would be more efficient than storing the same energy in ordinary chemical batteries, which is the current method for storing energy from natural sources for times of higher demand (or lower production, in the case of solar). Presumably their calculations are based on minimizing the inefficiencies for both batteries and compressed air.

Pumped storage systems - essentially hydroelectric systems with a top reservoir, a bottom reservoir, and a system of pumps to move water back up to the top reservoir at times of excess generating capacity - are used in the UK at Dinorwig and at Ffestiniog, and in the US at Luddington, Michigan (and probably in other places I don't know about). This is a reasonably simple, reasonably efficient system of storing energy at time of surplus production and releasing it at times of peak demand.

Re:How Efficient is It?

[Anomalyst]

We don't cache energy in your toilet, please don't pee in our pumped storage.

I don't believe it...

[AlienIntelligence]

I think those guys are full of vast hot air.

Re:Why air?

[srjh]

This doesn't compete with geothermal or tidal generation, so it's not necessarily any "better" or "worse". It's really more of an energy storage method (like a battery) that may even be useful as a supplement to something like geothermal generation. Store the energy at night when demand is low, and release it during the day when demand is high, and you'll smooth out variations in the power supply.

Also, you need a pressure difference to extract energy, just a high pressure is not good enough (similar to the fact that you can't extract electrical power from heat alone - you also need a cold reservoir).

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Not really new news?

[inflex]

This has been done on large scales by a couple of power plants in the past.

http://en.wikipedia.org/wiki/Compressed_air_energy_storage

Kubla Khan

[lazyDog86]

In Xanadu did Kubla Khan
a stately pleasure dome decree
where Aleph, the sacred river ran
down to caverns measureless to man...
from memory, apologies to Coleridge

Those words were famously written after an opium-induced hallucination, as was this plan

Flatulence

[riceboy50]

Yeah, I keep a lot of compressed air in my cavern. It's so powerful that sometimes I can't contain it any longer and it escapes. /ducks

Re:Why air?

[dbIII]

would be like using gravity for energy. If you find a way, let me know!

Easy:

1/ Lift musical instrument high into the air.

2/ Let go.

3/ Voila - energy from gravity!

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Ecofriendly?

[FrostDust]

Maybe I didn't understand the article well enough, but it just seems to me like they're using energy to compress air in caverns during the night, then using that air to make energy production during the day more efficient. Unless they're violating thermodynamics here, the amount of energy gained by using this compressed air system can't be more than the amount of energy used to compress this air into the caverns.

So, is it that only benefit here, cheaper energy costs, comes about because they're buying the energy when it's cheaper, and storing it for use when paying for this energy is more expensive?

Untapped reserves

[KlaymenDK]

Production ... used up all the easily available vacuum on earth (mined from the air which contained precious little vacuum! - bringing it down from space is not cost-effective!)

Oh, come off it. There are still plenty of untapped vacuum sources around.

There's about of cubic foot of the stuff in any PHB cranium, you just need to open the thing and tap it! Granted, you'd need quite a bit of source PHB, but that's easy enough to come by -- and it's renewable.

Re:Untapped reserves

[doug]

You're right that the transportation costs are low, but the mining costs are prohibitive. Those PHB skulls are so dense, so they chew up the drill bits like there's no tomorrow.

I believe that they are more effective as the power source for air turbines. Harnessing all that hot air that they produce to spin a turbine should generate countless megawatts. And it might justify some of the meetings that I've had to go to.

- doug

Re:How long will it last?

[dsvilko]

You mean cave-outs.

Hmmm

[bagsc]

Why not just put carbon dioxide down there, and burn more coal?

Re:Why air?

[jollyreaper]

Easy:

1/ Lift musical instrument high into the air.

2/ Let go.

3/ Viola - energy from gravity!

Corrected.