Even if less efficient, you can get enormous potential storage from pumped water with relatively simple machines compared to massive battery farms.
He also said the inertia of a falling weight is enormous, and would help stabilize the grid.
Now if you use water, pipes and pumps, instead of solid materials, now we’re talking. It’s called pumped hydro storage and is the number one grid scale storage in the world.
It is #1, just now, because a lot already existed. They cost a great deal to build, back when. New ones would cost as much, but a small variation is much cheaper, not needing a dam or a watershed.
A small variation on a bad idea can be a very good idea.
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.
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.)
Assuming utilities will do the stupid, expensive thing leads to failed analyses.
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.
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.
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.
The weight system only requires part of a hillside, has a pretty small environmental footprint, and there are lots and 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.
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.
Algorithms have been created to use GIS data to automatically find potential PHES sites. There are lots of candidates. Australia, for example, has 300x more potential that it would need for a 100% renewable grid.
If not, maybe there is a box canyon you can close the end of with a dam.
In places, they have flattened a convex hilltop and used the material to make a dike.
Usually you don't need anywhere near as much storage volume as a typical hydroelectric dam reservoir holds.
> efficiently
Are you sure about that? He said the losses due to pipe friction were considerable.
If the railroad is already built, and disused, that drives down cost.
Cost is what matters most.
The sweet spot for storage is near-zero opex, very low per-Wh stored capex, and cheap capex per-W in and, particularly, out. Thus, weight for watt-hours, and simple motor / generator for watts in and out.
Synthetic fuel has the appeal that the stored energy is readily tanked and transported, and very saleable; enough so to overcome low round-trip efficiency, expensive electrolysers for W-in, and complicated combined-cycle turbines for W-out.
This is partly because it needs no watershed, and partly because transmission lines mean it need not be local.
Anyway pumped hydro is only one of many equally viable alternatives. All will be used. Eventually which ones are cheapest will become clear.
None of these things exist at a large scale except for pumped hydro / water gravity, and that requires very convenient topography and geology to work. Generally, any non-chemical storage system is overpriced (too inefficient) or a maintenance disaster.
Not much storage exists because it has not been built yet. It has not been built yet because we haven't the renewable generating capacity to charge it from yet. Thus, we are spending on renewable generating capacity first, and lately factories that will build storage systems.
Battery storage is the most expensive variety. Round-trip efficiency is not very important anymore. I.e., other concerns dominate now. Anyway, gravity storage efficiency has always been fine.