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Comment by kordlessagain | Hacker News Reader

> Let's spin some numbers to further illustrate the poor energy density of gravity-based storage systems. Assume that you have a 100 kilogram lead weight that you can lower into a 10 meter deep hole in your yard.

> Now, how much energy can it store? This is given by potential energy formula E=mgh, thus E=100kg⋅9.8m/s2⋅10m=9.8kJ≈2.7Wh.

> For comparison, a single AA-sized battery stores about 2Wh of energy.

https://physics.stackexchange.com/questions/305563/why-dont-...

Wind turbine height: 99 meters. 100 kilogram lead weight == about a large person. So, a normal turbine maybe can hold about 100 people's worth of additional weight (elephant or two) * 10 (height multiplier) = ~1,000 AA batteries worth of stored power.

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If the stacking approach works at all, it must be because it is self-supporting. The material, once lifted, holds itself up.

At first it seems a bit silly that the bottom layers aren't lifted off the ground much at all, but if a tower is N meters high, the average height of each block is N/2, so that's only a factor of 2 loss. (For example, if each block were 1m tall, a stack of 100 of them would be 100m tall, and the average block would be 49.5m off the ground.)

And of course also because concrete is a combination of cheap, strong, and heavy. All of these serve as multipliers for energy storage practicality.

This excellently illustrates how a comparably weak force gravity is.

You also notice that when you go hiking on the mountains: it takes a lot of struggle to lose the weight that you gain with very little food. If you bring ham sandwiches, your net gain is probably positive...

Yes. Pretty much the opposite of the article headline, it's surprising how little energy you can store with gravity. When you do the maths, it's amazing pumped hydro works at all. And that's on the scale of cubic kilometres of water being lifted hundreds of metres - much more than any crane proposal.

Wow, I never really realized how good our current chemical battery technology is at being extremely dense.

Decades of incremental small percentage gains really adds up in overall terms.

Relative to kinetic/gravity storage, yes.

Relative to combustibles such as hydrocarbons, ammonia, or hydrogen, not so much.

(It's possible to synthesize carbon-neutral hydrocarbons, though with high round-trip losses, and not yet proved at scale.)

Our battery tech is pretty impressive. However, this is also a clear example of how weak of a force gravity is, comparatively.

One simple demonstration is to look at how a small magnet can combat the gravity of the entire planet when it holds an metal object in place above the ground.

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