[arussellsaw]

Compressed air storage seems like a really appealing method, especially considering the low carbon footprint and massively longer lifetime than lithium batteries. This post covers it quite well https://solar.lowtechmagazine.com/2018/05/ditch-the-batterie... , I’d be really keen to see if compressed air can also be successful for independent households looking to go off grid or reduce dependence on the grid.

[lend000]

While it is appealing compared to many alternatives and is more portable for smaller settings, when used on an industrial scale like this giant battery, I wonder how it compares in overall utility to gravity batteries [0].

The nice thing about gravity batteries is that they can form a closed loop with water supply, too, pumping reclaimed water back up into reservoirs when there's excess power. I'd expect compressed air to have much higher energy density, but it would be interesting to see if anyone has the numbers.

[0] https://en.wikipedia.org/wiki/Gravity_battery

[ashtonkem]

Pumped water batteries are geographically limited, since they can basically only be installed wherever you could build a dam anyways.

[trickstra]

Yes, but you can be moving rocks up a hill on a train or cable car. Or concrete blocks up a crane. Geographic limitation solved.

[ashtonkem]

Rocks and hills are equally geographically limited.

Cranes would work, but I think you’re ignoring the massive difference in mass between what the biggest cranes in the world can lift and even the smallest reservoir.

[walrus01]

some people are trying this:

https://qz.com/1355672/stacking-concrete-blocks-is-a-surpris...

I believe there's a beta test facility under construction now.

[arethuza]

Still pretty small compared to pumped storage - they give a value of 20 megawatt-hours, the Cruachan pumped storage scheme (which isn't particularly large) stores 7.1 gigawatt hours:

https://en.wikipedia.org/wiki/Cruachan_Power_Station

[newyankee]

Are they efficient ?

[ashtonkem]

Pumped hydro hits about 80% efficiency. So if you’ve got the right geography for it, it’s one of the best choices available.

[disambiguation]

look into energy stored on energy invested

https://en.wikipedia.org/wiki/Energy_return_on_investment#ES...

according to the wiki, pumped hydroelectric storage has a ratio of 704 where as compressed air energy storage has a ratio of 792.

[gnramires]

Those methods are actually quite similar, they're all ultimately related (limited by) tensile strength of materials. So costs and specific energy densities (per construction material unit) are similar. An important figure is cost/tensile strenght I guess.

(Compressed air: limited by container tensile strength; gravity batteries: limited by strength of cables)

I suspect even the constants involved are the same (given the materials are almost uniformly under nominal load), although I don't have time to investigate right now (a good curiosity research topic!).

[istjohn]

They are storing liquid air at low pressure, so container tensile strength is not a limiting factor at all.

[trickstra]

I believe these ones are not limited by tensile strength: https://interestingengineering.com/concrete-gravity-trains-m.... They are a bit limited by available geography, but far less than say pumped hydro.

[gnramires]

Indeed! In this case it's the integrity and friction of the soil (of the hill) that's keeping the potential energy contained, and this hill soil is "free".

[sa1]

In my country, there are economic challenges: water isn't available everywhere, diverting water is not cheap, and it messes with water sharing agreements, which are a political issue in themselves.

[luma]

Gravity batteries only need mass, it needn’t be water: https://youtu.be/gn5AM75AGvw

[toomuchtodo]

As I once heard from a Wyoming rancher, “Whiskey’s for drinking, water’s for fighting.” Water rights are treacherous to navigate.

[PopeDotNinja]

It’s gonna get worse, too, with upstream countries building dams at the expense of downstream countries.

[sandworm101]

It has its own issues, not the least of which is safety. There is lots of energy in compressed air, that's the point. I would look heavily into the risks of structural fatigue. A lithium ion battery might catch fire, but an "air battery" can go boom.

[alex_duf]

Given that anything that contains energy can go boom, I think of all of them this one doesn't sound too bad. Probably local casualties but no risk of cancer for the next century, or ground pollution for the next decades.

[verelo]

Isn’t this the issue with any large battery? Water in large volumes can cause a lot of damage too. I suspect it’s hard to find a large battery that isn’t scary when mishandled.

[learc83]

Compressed air is much more dangerous than most other storage methods though. The failure mode tends to release stored energy very quickly.

[throwaway0a5e]

Joules are joules. A "grid scale" compressed air tank going pop is going to do a lot more damage in the immediate vicinity but won't do anything 50mi away. You can't say the same thing about a dam burst.

Just because it's dangerous in a way you're not used to doesn't mean it's more dangerous.

[learc83]

>Joules are joules.

When talking about battery failure how quickly the energy is released is important.

>A "grid scale" compressed air tank going pop is going to do a lot more damage in the immediate vicinity but won't do anything 50mi away. You can't say the same thing about a dam burst.

If your comparing it to an entire dam, then your looking at underground storage of compressed gas in caverns. For that I agree both are dangerous in different ways.

But the context I was talking about was compressed air tanks which are more comparable to chemical batteries and gravity storage. Catastrophic failure of compressed air tanks is generally going to be more destructive than many other similar alternatives.

>Just because it's dangerous in a way you're not used to doesn't mean it's more dangerous.

A large lithium battery is much less likely to level several buildings than an air tank storing a similar amount of energy. I'm not saying that the dangers of compressed air can't be engineered around, but by almost any reasonable, objective metric you could come up with, compressed air is more dangerous.

[sandworm101]

Yes. Look for the vids of scuba tanks gone wrong. I'd rather drive around with a propane tank in my trunk than a 5000psi air tank.

[csharptwdec19]

Depends on the materials...

TBF I'm pretty comfortable with a proper steel tank.

But, nowadays I'd be afraid to use any of the fiber wrapped ones. I remember in the middle of the 2000s when a lot of new companies jumped into the Fiber-wrapped tank market... and shortly thereafter there were a notable number of recalls in/around the bonding between the fiber and metal layers of the tanks.

And, mind you, this was all in the paintball industry, which was a field where many did not have an understanding of the dangers of a piece of fiberglass with 800-5000PSI pushing it somewhere.

Happened more than once:

phone rings

Boss working at field nearby: "Hey, someone might be coming across the street to try to fill a tank that we refused to fill because it was (damaged/out of hydro)"

Me: "Yeah, I turned them away 5 minutes ago."

Customer walks in

Customer: "Hey the field said they were out of air but otherwise they would fill this."

[throwaway0a5e]

Literally anything you store energy in is going to have the same safety issue. You can muck around with space efficiency and peak wattage but at the end of the day you've got the same amount of joules that want out and if they get out in an uncontrolled manner it will be bad.

[woodandsteel]

This plant is not using compressed air, it's using liquified air.

[thinkcontext]

Several startups have tried and failed. Most notable was Lightsail which raised $80M from Gates, Thiel, etc.

[dhimes]

IIRC LightSail was founded by our own very brilliant Dani Fong.