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Comment by p1necone | Hacker News Reader

Are there many downsides to just lifting weights/pumping water up hills? What if you connected a lot of very large weights and electric motors to the grid and intelligently wound them up/let them down based on demand?

Maybe a two tiered approach combined with capacitors for fine tuning?

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Pumped hydro is by far the most commonly used utility-scale energy storage in use today. Efficiency is in the range of 70-80% so it's a lot better than compressed air in that regard, the main downside is that you just need a really large amount of water and a place to put all of it.

Lifting weights for energy storage is not really very conceptually different from pumped hydro (both store gravitational potential energy), water just happens to be vastly cheaper per ton than pretty much anything else. Concrete is something like $50 per ton and water is more like $0.50.

I wonder what it'd cost to use a waste material like slag. Slag weighs like 90% of the weight of concrete and is 10% of the price--because we basically throw it away. I guess the biggest cost would be containers to hold it. Even if the (cost container to hold slag + cost of slag) = (cost of equal weight concrete)--we're not using up concrete that could be used for things that actually need concrete. Here we just need something heavy that won't collapse when lifted. Plus, concrete releases co2 when poured. I guess co2 would have to be released to manufacture the containers--but even then...interesting thought.

How about instead of pushing water up into the air, you pulled air down into the water. Build a big floating object at sea and drag it down into the water with a cable attached to a motor/generator.

That's really clever. Only real downside is underwater maintenance is a PITA.

Although I suspect for the quantities involved, it still may be impractical.

Several similar approaches have been tested, although they use a turbine rather a moving chain to generate energy: http://euanmearns.com/a-review-of-underwater-compressed-air-....

I think you would have to use a vessel that could withstand underwater pressures. I imagine that would be on the expensive side, probably more expensive than the concrete blocks. And if the the vessel compresses at all, I think you loose efficiency due to the loss of buoyancy.

On a more general note, I think the issue with these novel storage methods is that even their more optimistic $/kWh targets are barely competitive with existing battery prices. And due to manufacturing scale, battery prices are expected to continue to decline. A similar thing happened in the solar market. Prices were really high, which led to a bunch of startups attempting to bring novel technologies to market (Solyndra was one of them), but once China started flexing its manufacturing muscle, PV prices dropped and the novel technologies had no hope of competing.

Here's a patent for a system like that: https://patents.google.com/patent/US20100107627

The main downside is that you need a place to store the water at the top. Favorable geography is most likely already in use. And building new lakes on hill tops alters the ecosystem quite a bit.

> Favorable geography is most likely already in use.

Favorable geography ON RIVERS is limited. Off rivers, the possibilities are enormous and largely unexploited.

Off rivers it's hard to get a sustainable supply of the huge amounts of water required to make a reasonably large operation to work.

No, not really. The evaporative losses are significantly less than a water-cooled thermal power plant of similar average capacity, even in desert conditions. And compared to water extraction for irrigation the water needs even to charge the reservoirs would be modest.

This startup is stacking concrete blocks as a 'battery'

https://qz.com/1355672/stacking-concrete-blocks-is-a-surpris...

It's bullshit.

https://www.youtube.com/watch?v=NIhCuzxNvv0

That is a poor quality source. A lot of "hand wavy" arguments with little to no citations.

That looks interesting, I hope the company succeeds and we see more of this.

Side note, the article has a comment about peak summer power usage that made me laugh out loud:

> For example, Mumbai hits peak consumption in the summer when air conditioners are on full blast, whereas London peaks in winters because of household heating. Ideally, energy captured in one season could be stored for months during low-use seasons, and then deployed later in the high-use seasons.

It seems hilarious to talk about storing power to run AC in order to solve an excess of heat problem. I honestly feel bad for people who die in heat waves in large cities, but it seems pretty absurd that we’re not already running AC cooling on solar like everywhere.

Vast size.

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