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It’s actually not a good idea at all. When you do the math ( or rather the physics) gravity batteries need so much mass and height to compete with other technol

It’s actually not a good idea at all. When you do the math ( or rather the physics) gravity batteries need so much mass and height to compete with other technologies that it’s just not worth it. Except if water, pipes and pumps are used, as water is heavy, and pipes and pumps can transport a lot of it very efficiently and cheaply. That’s called pumped hydro storage and is currently the #1 grid scale storage in the world. Trying to do the same with solid materials can sound like a genius idea but it’s really not.

WalterBright 4y ago
Well, his company is building a pilot plant in Brazil. I suppose we'll find out if he's a genius or not. > efficiently Are you sure about that? He said the losses due to pipe friction were considerable.
- ncmncm 4y ago
  Losses turn out not to matter much when opex is near zero and generation capex is very low. You just build a little more top-line generating capacity.
- qsdf38100 4y ago
  70% round trop efficiency. And it’s from actual operational data, not from an optimistic spreadsheet calculation.
  - ncmncm 4y ago
    70% is plenty, nowadays. If the railroad is already built, and disused, that drives down cost. Cost is what matters most.
ncmncm 4y ago
You need a very, very large mass, and then rails and rolling stock to carry it. That is why vertical motion in a disused mineshaft is attractive. A single 10,000t weight hanging from a winch has just one moving part, the winch, and cable all in tension, with no preparation of the shaft sides; everything is concentrated at the top. The mineshaft provides isolation from environmental disruption. You get much the same effect with a float attached to a cable down to a pulley augered into the sea floor; thence to an onshore winch. The cable and pulley are exposed to sea (or lake) water, but you get the advantage that the winch may be shared among as many cable reels as you like, with only simple clutches. A 20m diameter float displaces 4000 tons of water, and the sea floor may be much more than a km deep. (In principle you could share a winch drive among lots of mineshafts, but they are rarely close enough together. You could bore more, but that drives up cost. The world is absolutely perforated with disused mineshafts.)
- sanderjd 4y ago
  I hadn't heard this sea float / winch idea before! Any links you could dig up for me? Anyone operationalizing this yet?
  - ncmncm 4y ago
    There was an "Undecided with Matt Ferrell" on YT some weeks back that mentioned a dumb version of it somebody at a university promoted. That one had the winch and motor / generator at the sea floor, and a big rack of floats. It was, of course, too expensive. This is a common feature of energy storage ideas: people seem to love to promote the most stupidly expensive version of a good idea, and then give up when it is shot down for that. Certainly, any scheme where you put complicated electromechanical stuff on the sea floor, it will be expensive. And likewise, where the expensive part is only usable with one "unit" of storage. Or anyway it just costs too much or needs perfect weather or something. (E.g., Energy Vault (NRGV) is stupid and their investors will lose their shirts.) But there is usually a simple variation that lacks these problems.
- qsdf38100 4y ago
  10,000t weight? If it’s made up of rock with a density of 3000kg/m3, it’s 3333 cubic meters, so about 15x15x15 m3. Basically a large building. I’m not sure what kind of shaft can handle it. And even if you can pull it of, 10000t over 1000 meters is only 27 MWh of storage. 1 pumped hydro plant can store hundred of GWh!
  - ncmncm 4y ago
    (1) Rock is not very dense; pig iron density is 3x rock's. (2) A cube is not the only shape, for a weight. (3) Total capacity is not the only parameter of interest, for utility storage. (4) There is not only one mineshaft. (5) No utility is restricted to using only one kind of storage; different kinds favor different parameters, and we may expect utilities to use different kinds at the same time to maximize value and minimize cost. Assuming utilities will do the stupid, expensive thing leads to failed analyses.
WalterBright 4y ago
The downside of pumped water, of course, is you need a hydroelectric dam and there are not many sites suitable for that. Those dams also come with significant environmental disruption. The weight system only requires part of a hillside, has a pretty small environmental footprint, and there are lots and lots of hills.
- ncmncm 4y ago
  Not true. You can pump water to an existing hydroelectric dam, but you can also just pump it to a pond on a hilltop. No environmental disruption. There are lots of hills. The rail system needs maintained rolling stock and maintained rails. The mineshaft method is overwhelmingly cheaper and more reliable, because all that must be kept working is an electric winch. There are lots and lots of disused mineshafts.
  - WalterBright 4y ago
    Sorry, you can't make hydropower without constructing a dam, turbines, and completely disrupting the stream. This is environmentally destructive, and due to the scale needed, there are few suitable sites. There are indeed many unused mineshafts, but a shaft would be only suitable for a small weight, maybe enough for a single house. This does not scale.
    - pfdietz 4y ago
      Pumped hydro doesn't require a stream, since it isn't harvesting energy from a preexisting flow of water.
      - WalterBright 4y ago
        How are you going to create a large enough pond?
        ncmncm 4y ago
        Maybe read up? When you just make shit up as you go along, you say dumb things.

WalterBright 4y ago

Well, his company is building a pilot plant in Brazil. I suppose we'll find out if he's a genius or not. > efficiently Are you sure about that? He said the losses due to pipe friction were considerable.

ncmncm 4y ago
Losses turn out not to matter much when opex is near zero and generation capex is very low. You just build a little more top-line generating capacity.
qsdf38100 4y ago
70% round trop efficiency. And it’s from actual operational data, not from an optimistic spreadsheet calculation.
- ncmncm 4y ago
  70% is plenty, nowadays. If the railroad is already built, and disused, that drives down cost. Cost is what matters most.

ncmncm 4y ago

You need a very, very large mass, and then rails and rolling stock to carry it. That is why vertical motion in a disused mineshaft is attractive. A single 10,000t weight hanging from a winch has just one moving part, the winch, and cable all in tension, with no preparation of the shaft sides; everything is concentrated at the top. The mineshaft provides isolation from environmental disruption. You get much the same effect with a float attached to a cable down to a pulley augered into the sea floor; thence to an onshore winch. The cable and pulley are exposed to sea (or lake) water, but you get the advantage that the winch may be shared among as many cable reels as you like, with only simple clutches. A 20m diameter float displaces 4000 tons of water, and the sea floor may be much more than a km deep. (In principle you could share a winch drive among lots of mineshafts, but they are rarely close enough together. You could bore more, but that drives up cost. The world is absolutely perforated with disused mineshafts.)

sanderjd 4y ago
I hadn't heard this sea float / winch idea before! Any links you could dig up for me? Anyone operationalizing this yet?
- ncmncm 4y ago
  There was an "Undecided with Matt Ferrell" on YT some weeks back that mentioned a dumb version of it somebody at a university promoted. That one had the winch and motor / generator at the sea floor, and a big rack of floats. It was, of course, too expensive. This is a common feature of energy storage ideas: people seem to love to promote the most stupidly expensive version of a good idea, and then give up when it is shot down for that. Certainly, any scheme where you put complicated electromechanical stuff on the sea floor, it will be expensive. And likewise, where the expensive part is only usable with one "unit" of storage. Or anyway it just costs too much or needs perfect weather or something. (E.g., Energy Vault (NRGV) is stupid and their investors will lose their shirts.) But there is usually a simple variation that lacks these problems.
qsdf38100 4y ago
10,000t weight? If it’s made up of rock with a density of 3000kg/m3, it’s 3333 cubic meters, so about 15x15x15 m3. Basically a large building. I’m not sure what kind of shaft can handle it. And even if you can pull it of, 10000t over 1000 meters is only 27 MWh of storage. 1 pumped hydro plant can store hundred of GWh!
- ncmncm 4y ago
  (1) Rock is not very dense; pig iron density is 3x rock's. (2) A cube is not the only shape, for a weight. (3) Total capacity is not the only parameter of interest, for utility storage. (4) There is not only one mineshaft. (5) No utility is restricted to using only one kind of storage; different kinds favor different parameters, and we may expect utilities to use different kinds at the same time to maximize value and minimize cost. Assuming utilities will do the stupid, expensive thing leads to failed analyses.

WalterBright 4y ago

The downside of pumped water, of course, is you need a hydroelectric dam and there are not many sites suitable for that. Those dams also come with significant environmental disruption. The weight system only requires part of a hillside, has a pretty small environmental footprint, and there are lots and lots of hills.

ncmncm 4y ago
Not true. You can pump water to an existing hydroelectric dam, but you can also just pump it to a pond on a hilltop. No environmental disruption. There are lots of hills. The rail system needs maintained rolling stock and maintained rails. The mineshaft method is overwhelmingly cheaper and more reliable, because all that must be kept working is an electric winch. There are lots and lots of disused mineshafts.
- WalterBright 4y ago
  Sorry, you can't make hydropower without constructing a dam, turbines, and completely disrupting the stream. This is environmentally destructive, and due to the scale needed, there are few suitable sites. There are indeed many unused mineshafts, but a shaft would be only suitable for a small weight, maybe enough for a single house. This does not scale.
  - pfdietz 4y ago
    Pumped hydro doesn't require a stream, since it isn't harvesting energy from a preexisting flow of water.
    - WalterBright 4y ago
      How are you going to create a large enough pond?
      - ncmncm 4y ago
        Maybe read up? When you just make shit up as you go along, you say dumb things.