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?

 

[TheTick]

@ 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.

They could build a shell and fill it with rubble from the dig.

 

[btrueblood]

Tick, They'd still have to process the entire volume of the dig, no? Unless you propose to use an existing hole (maybe infill an old pit mine?).

Mint, double checking, for 150 o.d. x 150 ht. piston, volume is about 2.65 x 10^6 m^3, mass (assume 2750 kg/m^3) is 7.3 x 10^9 kg, yielding about 4.04 MPa lift pressure required neglecting any buoyancy correction, or about 586 psi.

At 290 MPa, you'd be worried about the granite being crushed (compressive strength of typical granite is around/north of 200 MPa).

Here's a fun idea: build condos atop the piston, and advertise as view property.

 

[TheTick]

Doesn't really matter. The primary purpose of this venture is to separate investors from their money. Energy production is just a potential side effect.

 

[miningman]

Well as someone who knows a bit about rock excavation, and dealing with all the fractures and slip planes, I am not going to comment on the practicality of excavating the rock, but lets just say I am not rushing to invest in this.

But to trueblood's estimates, his values might be realistic at a depth below surface of 300-500 metres but close to surface, no way. Without getting into technicalities, its all "rotten rock" down to 100 metres or so. This is due to geological forces / erosion over the eons. And if it were attempted, its not crushing of the rock that I'd be worried about, its hydrofracturing where the hydraulic pressures involved start to open up the microfractures in the rock and all of a sudden you've got no lift pressure because its all being bled away into the surrounding rock. And please don't suggest grouting. Bin there done that , know its limitations.

 

[IRstuff]

The 4 MPa value is if your pump outlet was that are, but it's not. I think the 290 MPa value would be for a pump with about 18-m OD, still pretty gigantic, possibly manageable.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[btrueblood]

Mining,

By my estimates, I assume you are referring to the crush strength of the rock. Agree, the 200 MPa value is probably for slabs/chunks used in buildings, not for raw rock with fissures and seams as you say. I was just trying to figure out if my numbers for the lift pressure were way off...290 MPa is pushing things even for mild steel...I'm pretty sure the actual pressure in the lift cylinder will be on the order of hundreds to a thousand psi (dep. on height of piston and number of condos atop it), but not 42000 psi.

IRStuff...hunh? Pressure to lift a granite cylinder is what I calculated, not sure why you think the pump outlet area factors in?

 

[BUGGAR]

This is just pumped storage with pumps lifting a rock instead of lifting water. Different strokes, I guess.

 

[rb1957]

how much work does it take to pump the water in ?

how much energy do you get back out ?

What you want is an anti-gravity device to temporarily take the weight of the pump, fill hole with water, restore weight to pump to pressurise the water.

another day in paradise, or is paradise one day closer ?

 

[KENAT]

I believe the term is Hydraulic Accumulator, very 19th century;.-)

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[btrueblood]

Kenat,

Yeah, but with gravity rather than a spring or pneumatic energy storage. To be true 19th century, it would be a steam lift, not water, and have a lot more brasswork and decorative cast iron

The first time I ever heard about gasometers was when reading Simon Winchester's book about Krakatoa - apparently the blast wave was recorded on gasometer level recorders across the world (ok, mostly in Europe), including several reverberations.

 

[MartinLe]

I'm still unsure if we can know the inner structure, little fissures etc. of a 100m bedrock plug.

From the site:
"The Gravity Storage is cut out of surrounding rocks. Because rocks nearly always have crevasses and fine cracks through which water can flow, it is necessary to completely seal the piston and the surrounding piston cylinder against the surrounding area.
For this purpose, all freely exposed surfaces are sealed with a geomembrane and concrete."

Plausible/workable?

 

[miningman]

no

 

[btrueblood]

Hmm. Not sure I completely agree with miningman. Dams, tunnels, and reservoirs are built routinely and sealed well enough (or pumped out fast enough?) to mostly prevent failures of the systems (lots of counterexamples, so "mostly" is justified). So, yes, leakage of the "cylinder cavity" could be minimized well enough to preclude complete failure of the system, given enough money and time. Mainly because the stresses involved are compression in nature.

I'm not at all certain, and I think miningman's gripe may also be: there is no way to guarantee the integrity of the piston rock, and failure of that rock along a seam (i.e. shear or tensile stresses) means a big chunk could come loose, with some fairly dramatic consequences. Ain't no geomembrane gonna hold up 150 tons of rock.

 

[TheTick]

Probably better just to hoist the plug up and down with pulleys. No leakage and simpler maintenance.

The whole thing has the ring of someone who is a little too enamored with his own concept.

 

[HamburgerHelper]

Using a rail up a large hill seems like a simpler and more reliable version of this same concept.

https://www.scientificamerican.com/article/energy-storage-hits-the-rails-out-west/

Seperately, how come no one talks about thermal storage?

 

[IRstuff]

Thermal storage invariably has leakage and losses. Moreover, it's difficult to maintain its quality factor, i.e., how much energy per unit time is extractable. If you were able to store molten sodium or similar, then the "quality" is "high" since you can use the large temperature difference to convert the thermal into, say, electrical. But, the high temperature difference makes the losses significant. Storing the water at, say, 95C, does not provide you with as many options for energy conversion, so its "quality" is low, but the thermal losses are substantially smaller.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[FoxRox]

I like the rail cars a lot better. Seems like it could be scaled to just about any size. Just need more rails, cars, and transmission. However, It wouldn't be much use out here on the plains of Kansas, where we make a lot of that pesky intermittent wind energy. If we could get one of those 500 kV DC lines out to the front range, then we would have something.

 

[cranky108]

Or maybe a rail up and down that mine shaft they just purchased.

Just a thought, but don't crystals generate a voltage when compressed? Or is it when the compression changes?

Or maybe just the difference in pressure between the upper lake and the cavity.

 

[MintJulep]

How would you build it?

Either start at the top, or start at the bottom.

Starting at the top:

Cut out the cylindrical kerf.
Line both surfaces with geotextile and concrete].
[highlight #EF2929]somehow[/highlight]support the giant cylinder of rock while excavating the disc below it.
Seal bottom of pit and cylinder.

Starting at the bottom:
Excavate a disc from the bottom and seal bottom of cylinder and bottom of pit.
[highlight #EF2929]somehow[/highlight] support the giant cylinder of rock while excavating the kerf around it.
Seal both cylindrical surfaces.

Not impossible I guess, although supporting a couple billion pounds of rock while working under or around it might not be so easy.

But is sure ain't gonna be cheap.

Doesn't seem economically viable.

 

[btrueblood]

Rail cars and mine hoists work...but to scale to the energy storage of the piston, takes a lot of railcars and a lot of acreage. In Nevada or similar, no big deal as there's lots of acres with steep inclines going idle right now.

If you drill vertically and use a simple hoist arrangement, it's a lot of drilling - probably more rock displaced than the piston concept at some scale.

But I like the idea of the railcars or mine hoists, because if one fails, you have a few dozen cars to scrape out of the pit at the bottom, while the next line over continues doing its thing. Not sure how you make the rock hydraulic accumulator piston idea redundant. But then, I still don't know how you'd make a 500 psi, 1m wide rolling diaphragm either.