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Comment by robinzfc | Hacker News Reader

To estimate the cost and practicality, assume you build a tower 120 meters tall and machinery able to lift 60 tons block of concrete to the top, then retrieve the stored energy by lowering it to the ground level. Think for a moment how much that would cost. Then calculate: mgh = 60000kg x 120m x 10m/s^2 (assume acceleration of gravity is 10m/s^2 for simplicity, no energy losses due to friction etc). The result is 72 million joules. That is 20 kilowatt-hours, about two days of a single household electricity usage.

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I love comments like the one above yours "just do this eyesore/expensive/impractical thing instead!"

Good enough is good enough. There is no one size fits all, and we really need to start leveraging everything we can to tackle energy storage. Each thing used doesn't need to be perfect for energy density, it just has to be good enough.

> assume you build a tower 120 meters tall.

vs sticking a concrete block in the ground like this paper is proposing.

As long as the durability is there, and it scales up like they say, this concrete block thing has interesting practical potential, because concrete is so ubiquitous. It's in foundations, it's in walls, it's in floors, it's under the road, sidewalk etc.

Heck, where I live we could turn our whole street in to one big battery to service the neighbourhood, while we couldn't possibly stick a whopping great big tower with concrete blocks in it, or a suitable size water tower.

All right, now assume making a 120m deep hole is cheaper than building a 120m tower. BTW, how many 120m deep holes have you seen in your life? You seem to be expert at them.

I have seen a few 120m towers. They call them skyscrappers.

Anyway, all this for 20Kwh. I can get a Nissan Leaf with a 40/60Kwh battery for way less than a skyscrapper. Most likely for way less than what it costs to make a 120m deep hole.

Long story short: cranes and concrete don't make a practical battery, but they make for many articles and publications.

Before you say "but lithium is hard to find, and concrete isn't": you can also make lead batteries, and ni/cd batteries, and liquid air batteries too. I don't expect the Earth to run out of air in the next decades.

Sorry, I guess I'm coming across wrongly somehow? I think 120m towers are crap as an energy storage solution. Maybe they could shove them inside skyscrapers that are being built, but that seems like a reach, especially given the size of the blocks needed for things to be practical. Leveraging existing mine shafts for it seems relatively sane. The work is done, it's unused, might as well get some ongoing value out of it, vs building a whole sodding great tower.

Static concrete being able to store power like a battery, like the article is talking about, is ideal if it works (possibly with caveats depending on how quickly it degrades). It's a ubiquitous material, used all over the place. It'd be getting value out of something that is going to be used anyway.

Gravity batteries are practical if you don't have to construct most of the infrastructure. Examples would include a bunch of mountains already there to construct a dam and have hydro pump storage, or an unusually nice and straight mine shaft that was already paid by the mine.

Anything heavy can be used as a gravity battery. Water in hydro pump for example. Or lead, or concrete. Lead is not that cheap, concrete is not that effective. For water we usually have already constructed a dam, it's just a case of adding another pipe and a pump.

But I guarantee you that if we were to construct a dam, pipe and pump just for energy storage - instead of taking an already existing dam we built for another reason, it would also not be as good as a bunch of batteries in pretty much all relevant factors.

Or you could avoid building the machinery and just pump water up and down. Then to lower the cost you could drop the tower idea and use a natural hill with reservoir on top. Surprise, surprise you just invented a pumped-storage power station.

Pumped hydro is great, but there are relatively few geographic areas where the terrain is suitable. You need a valley that can be dammed to fill a reservoir, enough water that it actually becomes a reservoir, and then a gentle enough slope coming out of the dam that you can build a secondary reservoir with enough water to capture the outflow of whatever period of time you're storing the energy and pump it back in.

California is one potential location, and there's been a lot of interest in pumped hydro from the California Department of Energy (and utilities), but I doubt it'd work as well nationwide.

Dig a 1300m shaft in the ground. Robots would be ideal for construction, as a large cistern would need to be built at the bottom.

I recalled a company doing exactly that design (but 60m high), EnergyVault - I think they also had mineshaft-based projects too. The cranes stack the weights, so there's a lot more than one weight.

Checking their site, I see they currently have a 100MWh storage under construction in china, with a different, boxy-building design. No idea on costs. https://www.energyvault.com/project-cn-rudong

>assume you build a tower 120 meters

I think the more popular approach is to use a deep hole, like a mine shaft. Maybe depth measured in kms. Because you're suspending from above you might be able to get a bit heavier than 60 tons.

useage in this manner could lead to a mineshaft gap

A kilometer deep hole is not very cheap.

Lets make them cheap. What is the minimum shaft size to get construction equipment to the bottom?

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