The energy density of mechanical storage is pretty terrible, and you need the right geography to help.

> and you need the right geography to help.

That's true of things like pumping water upstream, but I was thinking of something like this: https://qz.com/1355672/stacking-concrete-blocks-is-a-surpris...

I'm curious how much real estate it would take with that approach to equal the energy storage capacity of the Tesla battery.

I always heard that gravity was very poor for energy storage because it's such a relatively week energy. I haven't done the math so I'm not outright dismissing the idea but your article states:

>A 120-meter (nearly 400-foot) tall, six-armed crane stands in the middle. In the discharged state, concrete cylinders weighing 35 metric tons each are neatly stacked around the crane far below the crane arms.[...]

>The system is “fully charged” when the crane has created a tower of concrete blocks around it. The total energy that can be stored in the tower is 20 megawatt-hours (MWh), enough to power 2,000 Swiss homes for a whole day.

That seems like a huge hassle for a relatively meager storage. You'd need more than 6 of these to match Tesla's giant battery. Sounds like it would be an eye-sore too, but that's always a bit subjective. Maintenance-wise it could be rather tricky too, the article mentions complex systems to lift the blocks.

That thing is never going to be commercial viable. It doesn't have the energy density to be worthwhile, and comes with all the hassle that a moving mechanical system brings (maintenance etc). Plus I don't believe their 85% efficiency figure. That's ludicrously good.

Also most of the $40m/year saving of this battery is that it can respond in 100 ms which means they don't have to spend so much money buying electricity from other people when demand or supply changes suddenly.

That article says that one tower fully stacked is 20 MW, while the Tesla storage is 6 and a half times that. You can somewhat compare pictures between the articles to get a sense of scale.

Seems to me the Tesla system would have a much lower total cost of ownership as its a solid state system (and perhaps even construction costs - getting that much concrete in one place for the tower system would be a large expense). Plus the batteries can respond much faster and more efficiently to changes in electricity needs.

Moving parts are a big downside.

That's just a specific type of gravity battery. The primary issue is the low power to weight ratio. Consider that pumped water is also a gravity battery. Think of how much water is behind one of those dams.

Everyone overestimates how big gravitational potential energy is. That why we get companies peddling nonsense like energy harvesting pavements and speed bumps.

Exactly. Ultimately all energy storage has to be in one of the four fundamental fields; we've not yet harnessed the "strong interaction", the "weak interaction" gives us fission and fusion, chemical storage is effectively using electromagnetism at the atomic scale, and gravity is the weakest of them all.

For sure weights stored on railcars on hilltops (no existing commercial installs I know of) ... or the already widespread pumped-water storage ... would take a few seconds to come up to speed (compared to the 100ms for the Tesla). So clearly the battery will always win in unplanned outages.

Near-term, the batteries will probably be more expensive (replacement) than well-maintained mechanical/gravity systems. Longer-term, upcoming battery solutions may erase that advantage.

Think of it as the equivalent to high frequency trading vs long term investment. There is a need for both, and battery tech is the best at high frequency trading.

This is a small battery. The grid is very large.