4 ms·

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 10,0

by 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.
  - qsdf38100 4y ago
    Rock is cheap. The shape is irrelevant. For grid scale, total capacity is what makes it grid scale. No amount of parameter tuning can change the fact that stored energy is at best mass * g * height. Adding more huge mineshafts is irrelevant. You can always add more units, it doesn’t make it more efficient. Sounds like an Elon Musk solution. Make it bigger, taller, make more of it, and somehow it’ll bend basic physics facts to become the ground breaking disruptor technology of the next century.
    - ncmncm 4y ago
      Efficiency doesn't matter nearly so much as is usually assumed. What matters is cost. Exactly, cost per Wh stored, and per W in and per W out. Mineshaft storage is very, very efficient, but has an upper limit on energy per mineshaft determined by its depth and how much weight fits in it. The cost of the winch apparatus is amortized over that amount. More mineshafts means more total storage. Pumped hydro has very, very low cost per Wh stored, but kinda high per W in and out. But thousands of pumped hydro systems were already built, almost, so seem free; they just needed pumps added. Synthetic H2 and NH3 are very, very cheap per Wh stored. W out uses existing turbines, so seems cheap. W in depends on your electrolysers, which are improving fast. In batteries, cost per Wh stored has been large, but is different in different chemistries. In a better chemistry it is lower. Flow batteries have lower cost per Wh stored, for any liquid chemistry, but higher per W in or out; and need plumbing and pumps. Details matter. Numbers matter. Dumb choices make dumb designs. Dumb designs can be improved on. Drawing conclusions based on dumb choices is just dumb. Musk is dumb, but just barely smart enough to hire smart people and, sometimes, let them be smart. So, Hyperloop was just dumb, no matter who works on it. Starship is kinda smart, depending on what you can think of to do with it. Mars colonization is dumb. Starlink could possibly be smart, depending on a lot of details. A wholly new capability, like radically cheaper mass to orbit, can often enable smart ideas. Super-expensive mass to orbit was good enough for weather satellites, planetary probes, and geosynch COMSATs.

by ncmncm 4y ago

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.
- qsdf38100 4y ago
  Rock is cheap. The shape is irrelevant. For grid scale, total capacity is what makes it grid scale. No amount of parameter tuning can change the fact that stored energy is at best mass * g * height. Adding more huge mineshafts is irrelevant. You can always add more units, it doesn’t make it more efficient. Sounds like an Elon Musk solution. Make it bigger, taller, make more of it, and somehow it’ll bend basic physics facts to become the ground breaking disruptor technology of the next century.
  - ncmncm 4y ago
    Efficiency doesn't matter nearly so much as is usually assumed. What matters is cost. Exactly, cost per Wh stored, and per W in and per W out. Mineshaft storage is very, very efficient, but has an upper limit on energy per mineshaft determined by its depth and how much weight fits in it. The cost of the winch apparatus is amortized over that amount. More mineshafts means more total storage. Pumped hydro has very, very low cost per Wh stored, but kinda high per W in and out. But thousands of pumped hydro systems were already built, almost, so seem free; they just needed pumps added. Synthetic H2 and NH3 are very, very cheap per Wh stored. W out uses existing turbines, so seems cheap. W in depends on your electrolysers, which are improving fast. In batteries, cost per Wh stored has been large, but is different in different chemistries. In a better chemistry it is lower. Flow batteries have lower cost per Wh stored, for any liquid chemistry, but higher per W in or out; and need plumbing and pumps. Details matter. Numbers matter. Dumb choices make dumb designs. Dumb designs can be improved on. Drawing conclusions based on dumb choices is just dumb. Musk is dumb, but just barely smart enough to hire smart people and, sometimes, let them be smart. So, Hyperloop was just dumb, no matter who works on it. Starship is kinda smart, depending on what you can think of to do with it. Mars colonization is dumb. Starlink could possibly be smart, depending on a lot of details. A wholly new capability, like radically cheaper mass to orbit, can often enable smart ideas. Super-expensive mass to orbit was good enough for weather satellites, planetary probes, and geosynch COMSATs.