First off, don't be rude. Second off, bold claim saying I don't know shit about shit when you don't know that a gravity battery is measured in mass (or volume, sure) and height, you know, that thing that gravity needs to make stuff move.

Edit: Also, batteries don't directly power cities, they just smooth out power generation, but I'll show how a large enough battery could provide more than enough power if all other generation went offline and it could charge to full when that power was online.

Anyways, I'm too lazy to calculate this myself, but the Hoover Dam website has better data than I do and probably smarter people doing the formulas anyways. It produces 4 billion kWh of power per year on average. The power usage of a city of 1,000,000 people varies based on average headcount of each household and especially by industrial (and commercial) consumption compared to residential consumption, but to take NYC as an example, it uses about 11 million kWh per day, and has a population of about 8 million, so it uses about 1.375 kWh per person per day. Over the course of a year, this means that a city of 1 million people would take 1.375*365*1,000,000 = 500 million kWh for a year. Conclusion: the Hoover Dam, which is a gravity battery, could fully power 8 cities of 1 million people, or almost exactly 1 New York City.

[–] PowerCrazy@lemmy.ml -5 points 4 months ago* (last edited 4 months ago) (2 children)

I'll accept your math. So now in-order to solve america's storage problem to convert to a 100% renewable grid, we just need to build (Population of the US) / (Population of NYC) = 340million / 8million = ~43 Hoover dams. Do you think that is maybe a non-trivial problem to solve?

Don't forget that we also need the ~250sq miles of reservoir space for each dam. (technically it's the volume that is important, but for reservoirs you are often limited by surface area because of the topology required)

[–] efstajas@lemmy.world 5 points 4 months ago* (last edited 4 months ago) (1 children)

You're glossing over the fact that the battery is a backup to kick in only when renewable production doesn't meet demand, and that much more space-efficient energy storage solutions exist, even if they lose more power to inefficiency.

[–] PowerCrazy@lemmy.ml 1 points 4 months ago* (last edited 4 months ago) (2 children)

That happens literally every night though and wind also doesn't blow 100% of the time. There are significant amounts of time where the sun isn't shining and the wind isn't blowing. The current solution to this issue that is used all around the world are fossil fuels. Renewables make up a trivial* amount of power production compared to fossil fuels, and as we phase out fossil fuels, the requirement for energy storage is going up drastically.

*<30% by 2030 is the prediction by the EIA

[–] efstajas@lemmy.world 2 points 4 months ago* (last edited 4 months ago)

That happens literally every night though and wind also doesn't blow 100% of the time.

Very true, but the fact that wind blows often and there's also varying amounts of direct sunlight during the day already massively decreases the amount of storage required for a grid. You don't need the capacity to cover 100% of energy usage, sustained, like you suggested earlier. Especially as grids become (geographically) larger and smarter — we need wind and sun somewhere to cover energy needed elsewhere — it doesn't have to be localized. Plus solar output obviously peaks during the day, when demand is also highest.

Renewables make up a trivial* amount

The percentage is absolutely not trivial today. Especially considering there are multiple large grids today that can easily sustain 50%+ renewable energy over sustained periods. And 30% by 2030 is a lot, though of course it could be a lot better.

and as we phase out fossil fuels, the requirement for energy storage is going up drastically.

Yes, no-one is arguing otherwise.

[–] Feathercrown@lemmy.world 1 points 4 months ago* (last edited 4 months ago)

30% is NOT trivial lmao

Do you know what else decreases when the sun goes down? Power demand.

[–] Feathercrown@lemmy.world 2 points 4 months ago (1 children)

If we built 43 Hoover Dams, we wouldn't need to build any other renewables at all-- the Hoover Dam doesn't just store power, it also generates it. I'm not sure of the numbers for pure pumped storage hydropower systems (I don't think "pure" systems even exist, everywhere gets some rain), but we only need enough capacity to take over when the normal grid is underproducing.

[–] Feathercrown@lemmy.world 2 points 4 months ago* (last edited 4 months ago)

To answer your actual question though, we need about 85 times our current pumped hydro capacity to transition to a fully renewable US. This seems daunting, but:

Pumped hydro is growing rapidly
It's not the only battery storage technology (heat batteries look promising imo)
Any increases in storage allow more renewables, less pollution, and overall contribute to making our future better

Pumped Hydro doesn't need to singlehandedly handle the storage load of the entire US because there are other options to use in conjunction with it and even a partial storage solution produces benefits. This is good, because Pumped Hydro is geographically limited.