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luxmesa t1_j0mc4xn wrote

Reply to comment by transmitthis in Switzerland’s Giant “Water Battery” Starts Working by Wagamaga

I wanted to do some quick math on this.

Let’s say you’re trying to replace a power wall. That’s 13.5 kWh or 48.6 MJ. It takes 9.8 joules to lift 1 kg to a height of 1 m in Earth’s gravity. Let’s say the height of your basement is 3 meters. The weight would need to be 1,650 metric tons to replace the powerwall.

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vAltyR47 t1_j0mvwsg wrote

I wanted to see how big this would actually need to be.

Let's say we're using cast iron. Density is 7800 kg/m^3, so you'd need approximately 211 cubic meters of solid cast iron, which is a cube with side length of approximately 6 meters. So you'd need two stories just to fit the thing in your house, and another to be able to lift the required amount.

So that's obviously impractical, let's use a denser metal. The densest metal material is osmium at 22,600 kg/m^3, resulting in a block 73 m^3 which is a cube with side length 4 meters, which still doesn't fit in your basement, but we can probably fit most of the mechanism into two stories.

The densest know element is hassium, which gets you down to a cube with side length 3.4 m, which still doesn't fit in your basement (let alone the height needed to lift) and has the minor drawback of a half-life of 10 seconds.

So short of exotic materials you generally only find in stars, such a system is fairly impractical on the household scale.

I think this example really highlights the main drawback of these kinds of energy storage systems: they take up a lot of volume.

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vellyr t1_j0n7ph5 wrote

Why is a six-meter cube impractical? Lots of people have that much space on their property in America, and you could easily make it taller/narrower and put most of it underground.

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jawshoeaw t1_j0o0ws2 wrote

Impractical for small suburban lots/homes. Quite feasible for larger properties. Of course water would probably be used as it’s readily available. Or maybe dirt /sand?

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Longjumping_Meat_138 t1_j0or66e wrote

Water is best, Dirt and Sand would be impractical. But we have to think about the fact that the Storage system together would be the size of two large cars. The issue with storage would be most problamatic and so would the cost of building these tanks. It could easily ho upto 20,000 dollars for two tanks if not higher.

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