This was a pretty novel approach that just showed up on my twitter wall:
Energy Vault to build grid-level, gravity-fed battery from a tower of concrete blocks -- Michael Irving -- November 8th, 2018
https://newatlas.com/energy-vault-concrete-tower-battery/57164/
...
Well, it's not really novel, gravity storage has been around for centuries. Ever see the weights on a Grandfather's clock?
So if this had much going for it, why wouldn't we see it used more already? There is demand for energy storage that can be quickly dispatched like this. There's really
nothing standing in the way. We understand the technology fully, nothing advanced is required. It's not like molten salt, next gen nuclear, batteries made of unobtanuium, or anything. We can do this today - we could have done it decades ago at scale.
I've researched this pretty deeply before on a tech forum. Sure, there are things about gravity storage that are attractive - simple, reliable, no advanced tech or materials, no long term losses, easy to understand, can be done safely. So why don't we do it?
Easy - just run some back of the envelope numbers. The math is simple, gravity x mass x height. It takes a LOT of mass, and a LOT of height to get much energy at all. I don't see anything in the linked article that describes the size required for these gravity towers, do you? "big?" Hmmmm?
Assuming "up to 35 MWh and 4 MW peak power" is in the same unit, it would take ~ 200 of these units to supply the power of one typical fossil fuel plant (~ 800 MW). And it would run out in less than 9 hours.
https://power-calculation.com/potential-energy-gravitational-calculator.php
For example, lift 3700 kg ( ~ 8200 pounds) 100 Meters (~ 328 feet), and you get a mere single, lonely kWh. Since a US home uses ~ 30 kWh per day, you need 30 of those to back up a single home for a day. Imagine 30 towers capable of supporting 8200 pounds 300 feet in the air on my property!
So, how big is this tower?
Also consider their claim of dispatching this energy in 2.9 seconds. Think about the incredible mechanical stresses of starting/stopping that amount of mass that quickly.
I wish you fans would actually critique this stuff objectively, and present numbers and context, rather than just post flying car dreams.
-ERD50