But I assume there's structural issues with suspending a few extra tons on your structure.
ARES (rail energy storage) builds a rail-line uphill, for example. Rail cannot handle a very steep slope, but a gentle hill climb will build up potential energy fine.
In the case of vertical-based gravity storage, I'd imagine that lifting blocks to the top of a cliff (or down a valley) would be most efficient.
I mean, Pumped Hydro is gravity storage, and does just that. Pumping water up a mountain and generating energy by dropping it back down. But presumably, we don't want to use water in the Western states (where water is scarce). So Gravity-energy storage WITHOUT water is the goal.
For example, all the dam failures that have obliterated entire towns.
I'd rather a failure obliterated a bunch of earthworms and voles.
I expect that the voles disagree with me.
There's hills somewhere in there, and those hills can form energy-storage solutions that can be transmitted across the entire MISO grid.
Bonus points: if you want to build a big battery in Iowa, you can take advantage of excess power in Iowa or Missouri. Building tiny batteries here and there will only lower your efficiency.
There's a reason why a lot of discussion here is on large 100s of MW proposals: because anything smaller won't really be a big win economically. And it shouldn't be too hard to fill up 100s of MW capacity because of the nature of our large and reliable power grids here in the USA.
Leading to ~10,000 feet (or nearly 2-miles) of elevation change. From there, you can dig another mile underground, leading to 1-mile (under ground), or -1000 feet elevation, to a peak elevation of 14,000.
If a tower were built on the top of the mountain: you could gain another 2000 feet or so on top: so maybe 16,000 (a 2000 foot tower on top of the mountain peak) to -1000ft (1-mile deep from the bottom of the 4000-ft elevation valley), for a total differential of 17,000 feet.
Ignoring earthquakes and other issues, of course. :-) Just purely from a hypothetical perspective: working with nature and the natural landscape seems like it'd be better than "just" digging a hole.
EDIT: Repurposing abandoned mine shafts might be worthwhile, depending how deep they are.
Gravitational potential energy is (approximately) linear in height. I say approximately because this assumes constant g (which is a good assumption when h is small compared to the radius of the earth, which it is).
And in fact, a consequence of gravity's 1/r^2 nature is that one is only subject to gravitational acceleration from what is beneath them (shells above cancel out), so mine shafts are less efficient than towers (the effect size is small to the depths we can mine).
So adding more height doesn't help, and if that height is underground it could actually hurt net efficiency.
Efficiency in this context refers potential energy stored per unit height. The field is conservative no matter what you build.
If you picture a dense weight like a cannon ball on the end of a string you're right, but if you're digging down n meters, encasing n/2 meters worth of dirt and moving it up and down the free n/2 meters of shaft, the energy storage would indeed be proportional to n^2.
I don't know anything about the field and had the same reaction you did, but considering parent is running a startup in it they're either a lunatic that doesn't know the equivalent of FizzBuzz or there's something we missed on first inspection, and we should charitably assume the latter...
The single shaft vs multiple parallel approach does seem a bit risky in the early days. If there's a 10% failure rate, and you built one shaft, that's a 10% chance of an existential threat to the company. 10 shorter shafts mean one will likely be inoperable.
Of course over the long term worrying about this doesn't make sense. Once you've scaled, 1k large vs 10k small shafts would not matter from this perspective.
Best of luck mate!
There's another thread on this comment page talking about why height is important. Please see this slide in our presentation illustrating it. https://docs.google.com/presentation/d/17FI-jrI9RWS3q7Ng44Yh...
Nah.
In exchange for nearly doubling the weight of the average 3MW tower, adding enormous complexity, you'd be able to boost power output to 3.02 MW for one hour.
That gets us back to the fundamental problem with gravity storage - it's all mgh. You want to store a lot of energy, you better have a shit-ton of either m, g, or h, and one of those numbers is already tough to change :)
I doubt that suspending the weight is the main structural issue. It's the high center of mass when the weight is at the top.
Regarding justifying the cost--obviously depends what the cost is. If it's really just the generator, cabling etc, it might work as a short term load balancer. I saw somewhere about GE investing $X millions to smooth turbine output over 5min intervals.