Any comments on this large energy storage device? 7

[MartinLe]

Look at this:

http://www.heindl-energy.com/

Essentially they plan to cut a large plug from bedrock, raise it by pumping water underneath to store energy:

The thing looks insane. They address a few design issues on their site. I'm unsure about the feasiblity, what do you think?

 

[CheckerHater]

Looks surprisingly similar to the idea of importing vacuum from space.

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[FoxRox]

With the lessons being learned in Oklahoma about pumping water underground at high pressure, I'd think we'd want to table this idea for now.

 

[JNieman]

water.... table.... I see what you did there.

 

[natepiercy]

If that concrete wall is strong enough, I don't see why this is a bad idea. It seems more feasible to dig a giant hole to store pressurized water than to build a giant tank many feet off the ground. Certainly, this is a more complicated system than a water tower, and I'd be curious to see how much additional energy loss there is in the system... But this looks like it will scale well into large sizes.

 

[MartinLe]

Can anyone with knowledge of mining comment on their approach to building the plug:

http://www.heindl-energy.com/gravity-storage/building-the-storage.html

To me it looks like they put a lot of thought into this and I don't see the huge flaw that makes it unbuildable. Still don't trust the idea.

 

[cranky108]

So how many locations would you find a large enough rocky base with few seams, and enough water?

Then after cutting the rock from the hole, you would need to seal it enough to keep the water from escaping around it.

Another thought is the rock would not need to be round, except that we like nice shapes. If big enough, one could place the solar panels or wind machines on the rock. Or one could even add to the rock after it has been excavated.

But in general, the problem looks to be the seals. But you would not need to use water, as high pressure air could also work (maybe not as well).

 

[KENAT]

cranky, that's why it has to be round - so the O-ring is easy to fit.

Massively scaled up version of the old style Gas Holders (Gasometer) of Oval cricket ground fame.

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[hendersdc]

Assuming they can build the thing and get it working in the first place maintenance and repair of cracks would be hell. Seems like you would need to have a completely uniform density in the piston to get it to ride evenly as well.

 

[JNieman]

I would think a system of ballast would be inconsequential.

 

[CheckerHater]

But you would not need to use water, as high pressure air could also work

Just think of how much damage the potato gun of this caliber can do.

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[IRstuff]

The roundness is partly to make sealing easier, but primarily, to make cutting easier. There's no good way to cut a square corner with their cutting approach.

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[btrueblood]

The more massive the piston, the less likely you know the internal structure very well, i.e. the location of seams/fissures that could rupture unexpectedly. Maybe it becomes a non-issue after the cylinder is filled and the piston is "floating" with uniform pressure around the sides, but it would sure be worrisome during the excavation.

I'd not worry tremendously about the static seals along the walls and floor of the cylinder, but the rolling diaphragm piston seal...working at several tens to a hundred bars...across a meter or three of radial span? That's a pretty tricky job, given the seal will be formed in-situ, so no real chance of using cured elastomers. Not saying it's impossible, but we use rolling diaphragms in our products, and design for 100-200 psi is non-trivial in a long-stroke rolling diaphragm.

I'm also curious as to how uniform in density the piston rock will be. They show a system of rollers to guide the piston along the upper edge, but if the rock is heavier on one side, how many megatons do those rollers have to be designed for, and will the seal still get pinched if the piston tilts?

 

[HamburgerHelper]

The price for a kwh of lithium ion is dropping fast. Fast enough that energy storage for arbitrage could be feasible in the near future in expensive markets. In California, Telsa won a project for a huge battery bank that the SoCal Edison will use because they were afraid of a generation shortage due to a natural gas pipeline being damaged.

http://www.bloomberg.com/news/artic...e-battery-storage-after-porter-ranch-gas-leak

 

[ornerynorsk]

Looks like an absolute boondoggle, imho.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[MintJulep]

Scaling by eyeball vs. the power line towers the cylinder is roughly 150 m high and the same diameter.

Assuming granite.

Pressure needed to lift it is roughly 290 MPa (42,000 psi). 4 MPa (550 psi) [Thank you Btrueblood for checking my math]

I guess that's high enough to contain useful amounts of energy.

Should be an interesting turbine.

Designing the seal for the rock cylinder may be non-trivial.

I guess just coating the pit will flex seal will keep the water in.

 

[IRstuff]

Pretty interesting. So there are pumps that can generate that sort of pressure:

http://www.jetech.com/node/59

That pump will move the plug 0.7 mm/hr at 600 gpm flow.

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[TheTick]

I don't see why they are fixated on cutting the plug from bedrock. Surely a better one can be fabricated.

Good luck sealing.

 

[MartinLe]

@ Tick:
By cutting a plug from bedrock, they have a volume = surface area of plug x 3m to move, to manufacture a plug they would need to handle the whole volume. The theory is that their way, the costs scale with R², not R³.

@btrueblood
I think you raise good points.
To me (but I never designed one!) the rolling seal looked like a good idea. At the large size, you have little curvature so that certainly helps.
But you'd have to assemble the membrane in place, which doesnt help at all ...

Another point raised by btrueblood:
How well can we know the inner workings of such a large plug?

 

[moltenmetal]

HamburgerHelper: Li-ion automotive cells are already below $140/kWh and packs below $180/kWh, so your curves are already quite a bit out of date!

I still think that Li-ion isn't going to be the right tool for grid storage. Something with less energy density but with similar efficiency at significantly less $/kWh is going to be developed. Right now everyone is still racing after the highest energy density rather than digging through the old work to find a chemistry which can generate cheap cells with outstanding cycle life but with lousy energy density.

My bet is ultimately on flow batteries- they're significantly worse in efficiency but you can't beat their storage cost- tanks for holding liquid at room temperature and atmospheric pressure are very cheap indeed.