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Any comments on this large energy storage device?
7

Any comments on this large energy storage device?

RE: Any comments on this large energy storage device?

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

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

RE: Any comments on this large energy storage device?

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.

RE: Any comments on this large energy storage device?

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

RE: Any comments on this large energy storage device?

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.

RE: Any comments on this large energy storage device?

(OP)
Can anyone with knowledge of mining comment on their approach to building the plug: http://www.heindl-energy.com/gravity-storage/build...

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.

RE: Any comments on this large energy storage device?

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).

RE: Any comments on this large energy storage device?

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.

RE: Any comments on this large energy storage device?

I would think a system of ballast would be inconsequential.

RE: Any comments on this large energy storage device?

2

Quote (cranky108)

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.

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

RE: Any comments on this large energy storage device?

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?

RE: Any comments on this large energy storage device?

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/articles/2016-09-15/...

RE: Any comments on this large energy storage device?

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.

RE: Any comments on this large energy storage device?

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.

RE: Any comments on this large energy storage device?

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

Good luck sealing.

RE: Any comments on this large energy storage device?

(OP)
@ 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?

RE: Any comments on this large energy storage device?

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.

RE: Any comments on this large energy storage device?

Quote:

@ 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.

RE: Any comments on this large energy storage device?

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.

RE: Any comments on this large energy storage device?

3
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.

RE: Any comments on this large energy storage device?

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.

RE: Any comments on this large energy storage device?

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?

RE: Any comments on this large energy storage device?

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

RE: Any comments on this large energy storage device?

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 ?

RE: Any comments on this large energy storage device?

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.

RE: Any comments on this large energy storage device?

(OP)
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?

RE: Any comments on this large energy storage device?

no

RE: Any comments on this large energy storage device?

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.

RE: Any comments on this large energy storage device?

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.

RE: Any comments on this large energy storage device?

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! https://www.youtube.com/watch?v=BKorP55Aqvg
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RE: Any comments on this large energy storage device?

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.

RE: Any comments on this large energy storage device?

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.

RE: Any comments on this large energy storage device?

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].
somehowsupport 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.
somehow 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.

RE: Any comments on this large energy storage device?

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.

RE: Any comments on this large energy storage device?

All,
I would think that if this is a viable energy-storage alternative, we should have seen a scaled-down version (ie proof of concept) by now. N'est pas?
I don't see this thing taking off; too much risk.
GG


http://www.theglobeandmail.com/report-on-business/...

The pessimist sees difficulty in every opportunity. The optimist sees the opportunity in every difficulty.
Winston Churchill

RE: Any comments on this large energy storage device?

In some sense, the concept isn't really scaleable. The trench digger that cuts the cylindrical portion of the plunger cannot be arbitrarily shrunk, so there's a limitation on the kerf width around the cylinder, and therefore, a limitation on the cylinder width as well.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers

RE: Any comments on this large energy storage device?

If one put a large car park building on the top of the plug for a residential area one could get "free" energy. Cars leave during the day (reducing mass) when it is charging and return adding mass just before the start of peak power consumption.

Is it likely to act like a giant compass? (OK that would be dependent on the rock and its only going to move very slowly but its not a trivial mass to stop rotating).

RE: Any comments on this large energy storage device?

If it could act like a giant compass and it rotated in it's hole, would the world wobble?

RE: Any comments on this large energy storage device?

I wouldn't mind each day being a little longer.

RE: Any comments on this large energy storage device?

Days longer, year remains the same... assuming salaried paid, I'm coming out ahead!

RE: Any comments on this large energy storage device?

If you build a better mouse trap. But I have not seen efficiency numbers on any of the proposed schemes. Are any of them better than 50%?

At least with power plants there are numbers of Dollars per megawatt, which is a cost to construct. And there are heat rate numbers to help define the efficiency.

RE: Any comments on this large energy storage device?

RE: Any comments on this large energy storage device?

Conflating the storage of low grade heat with the storage of mechanical or electrical energy is not helpful...but it's a hamburgerhelpful graph.

RE: Any comments on this large energy storage device?

btrue, if I recall correctly some of the early hydraulic accumulators did just use a mass on top of the column of water. Quick look on Wikipedia didn't contradict it as I recall but I can't remember if it 100% confirmed it either.

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RE: Any comments on this large energy storage device?

Moltenmetal,

Hamburgerhelpful graph? I don't know what that means exactly but I like graphs so I'll roll with it.

These numbers line up with stuff I have seen elsewhere with the exception of thermal storage for electricity. Numbers I have seen elsewhere place it around 70-80%. None of these methods that I have seen use low grade thermal storage. All of them that I have run across on the web that are for grid energy storage use molten salts.

RE: Any comments on this large energy storage device?

(OP)
Heindl claims their dvice could be as efficient as pumped hydro, which makes sense.

Storage efficiency ~90% for heat can't mean electrical power as output. No heat engine that efficient.
Storing heat as heat OTOH makes a lot of sense.

RE: Any comments on this large energy storage device?

Considering size and pressure requirement for the pumps, wouldn't it be easier just to "reverse" hydro-electric station and pump water uphill, back into reservoir?

Pumped storage seems to be viable solution for years.

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

RE: Any comments on this large energy storage device?

(OP)
The idea is to have a smaller footprint than a valley (which is the usual footprint of pumped hydro). But let's do a dirty quick & calc if it actually holds up:

Let's say 100mx100m piston (DxH), density of 2600kg/m³, moving height 50m - Approx: 280MWh stored (potential energy of plug, ignoring water we pump down to move the plug up)

For the same potential energy you need at 50m pumped height 2 mill. m³ water.

How much water level fluctuation do you permit in the upper reservoir of your pumped hydro storage?
Let's say 1 m (my nearest plant has 70cm in the lower reservoir) so we arrive at 2 mill m² surface - 2km x 1km or so. A small valley.

The idea behind the plug is that we run out of good sites for pumped hydro sooner or later. Looking at what others in this thread have written, I now doubt there's a good site to build the plug.



RE: Any comments on this large energy storage device?

Actually you don't need a lower lake for pumped hydro. If you have a river where the water level is normally high enough, it can be used as your lower source.

Another method may not require any generation on the back end, in that water systems all over use a upper storage so they don't have to run pumps all the time. But if those upper storage were to expand, and the pumps only timed with the excess generation, then it would appear as a form of energy storage.

RE: Any comments on this large energy storage device?

Just thinking aloud here- I have read a little about this but have never designed or operated a hydro station- but I understand that in some cases there would be no real need for pumping at all- you'd just modulate the flow of water to the turbines and allow the upper reservoir level to rise while you're not running them. Some reservoirs can handle the variable level, and the downstream body of water can also handle the varying outflow, so some hydro facilities are used for "peaking" in this way. But most can't be used that way- their output can be modulated based on demand, but the excess water soon has to be spilled and its potential energy wasted when the full output isn't required.

The real problem with storage of any kind is that electricity is just too cheap to bother storing in most locales. Why would you want to build a facility capable of operating in this fashion unless there was a payback for the extra capital required? You'd need to build turbines capable of, say, 3x the average flow, and then operate them only 1/3 of the time.

RE: Any comments on this large energy storage device?

Actually we do operate some of the hydro plants at some fraction of their rated output most of the time. The reason is limited water flow, demand, maintaining water level, etc.
The fact is that people don't demand peak electricity or water all the time. Some people like a lake that does not have a daily high and low tide.

And some of our high lakes are frozen for part of the year, so the hydros are not operated during those months.

RE: Any comments on this large energy storage device?

Quote (moltenmetal )

The real problem with storage of any kind is that electricity is just too cheap to bother storing in most locales.

Well, the politicians and greens are working on the problem :)

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

RE: Any comments on this large energy storage device?

"doubt there's a good site to build the plug." ... someone else's back yard ?

so "at best" this'd make available 70% of the energy it took in ? so this is more about allowing the main line power stations run at constant, or at worse a slowly varying, load and so allow these to be more efficient. The point of this is to harness the potential energy of the plug. what sort of water pressure are we talking about ?

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

RE: Any comments on this large energy storage device?

"doubt there's a good site to build the plug." ... someone else's back yard ?
Not a bad idea. When a house connects to the water utility, they have to provide their own energy plug in their back yard. They could put a platform on it and give the kids a ride while storing and retrieving energy. The resources are all in place: pressure, quantity of media (except maybe during drought), distribution.

RE: Any comments on this large energy storage device?

Quote (KENAT)

if I recall correctly some of the early hydraulic accumulators did just use a mass on top of the column of water
You're right. There's still one like that works the machinery at Bristol Docks. There also used to be (may still be) one to lift the bascules at Tower Bridge in London.

A.

RE: Any comments on this large energy storage device?

Interesting, but the challenges presented are substantial, and the energy required to construct it will go unrecovered. Water storage is useful, but this mechanism would only be useful in certain situations, probably not in most parts of North America, Europe, China, much of South America, or northern Asia, because of the plenty of natural elevation changes, and within good transmission distances from utilization areas.

.


Me wrong? I'm just fine-tuning my sarcasm!

RE: Any comments on this large energy storage device?

2
I was down at the Underfall Yard in Bristol just after Christmas and grabbed a photo of the old accumulator.


Round the back, they have a cafe with a working model. Various relatives enjoyed being pumped up and down to play the part of the deadweight.


A

RE: Any comments on this large energy storage device?

Insane? No
Realistic? Equally no.
There's no way you can excavate a solid plug like that. You would never be able to cut the horizontal section unless you mined it out and then propped it up while you sealed the base of the"cylinder"

The cost of the concrete shell,the seal, the hundreds of rollers compared to the storage capacity must be uneconomic.

The pressure even of an un feasible 100m high plug is only 26 bar.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Any comments on this large energy storage device?

I believe a much more simpler and probably cheaper solution may be convert existing hydropower stations in to pumped storage plants. Build a small check dam at tail rise and pump water at day time and reverse flow to generate power at night.[link ]Link[/link]

RE: Any comments on this large energy storage device?

Raising an obelisk with pulleys and wire rope and hydraulic pump/motors might be sort of practical, but archaeologists have yet to figure out how the Egyptians made the horizontal cut to free the obelisk from the rock.

Giant o-rings or rolling bellows working against cut rock faces do not sound viable.

Mike Halloran
Pembroke Pines, FL, USA

RE: Any comments on this large energy storage device?

How to make it isn't all that impossible - just money.

If you want a narrow kerf, sink a shaft alongside the plug.
Dig horizontally to the edge of the future plug.
Dig a circular tunnel under the desired cut line.
Drill two small passages from the surface to the tunnel and feed cutting cable down one side, around a pulley in the tunnel, and then back up to the cutting rig through the other hole. The original holes can be filled with epoxy/cement and are cut to finished width with an overcut.
Move the cutting rig along the top and move a turning pulley along the bottom to make the cut.
When the plug side is finished, move the cable drive or turning pulleys to the bottom of the side shaft and place pulleys at either side of the opening, with the cable looped around the plug base.
As the cable cuts, backfill to support the plug and prevent cable pinching. Access to backfill the cut will be available immediately behind the cable as it advances.

Cable cutting does wonders on limestone and ships; no reason to believe that it can't work here, just a matter of cost/time.

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