I’m questioning the amount (which is what the whole argument about this being impractical is based on).
Do you really need to have a store of 11% of the city’s entire yearly energy usage? Like, 5 (almost 6!) entire weeks of energy? That seems ludicrously high to me.
Ok, let's say it's one week. Is that still ludicrously high? The scale of the challenge is the same. Storage via gravitational potential energy is not realistic, except if geography is on your side.
That was my point, that gravitational storage is surprisingly inefficient.
But since you challenged me on the 11%, I did some research, and now I think that storage may not even be needed (aside from the day-to-night storage via batteries, which is already economical nowadays).
The EIA gives [1] the US electricity generation by month and source for 2020 and 2021. Solar and wind are small nowadays, but if you were to scale to cover the entire annual needs of the US only with solar and wind, you'd get a profile where on some months you get more than you need and on some months you get less.
The longest stretch is in the Summer months (presumably because of AC). During those months, for 3 or 4 months in a row you produce less than you consume. You need about 6% or 7% of total annual consumption in storage to make up for the deficit. If we include conversion losses, and an additional buffer, then my original 11% sounds about right (although I just pulled it out of thin air).
However, if your just use natural gas for those 6-7%, then you don't need storage at all. Cutting the fossil fuel generation from the current 60% to 6% means reducing emissions by more than 90% (lost of current generation is from coal, which emits about double the CO2 than the equivalent gas generation).
You can also overbuild solar and wind a bit, let's say by 20%, and the deficit gets reduced from 6-7% to less than 3%. You can then balance the load using the hydropower that we already have.
So, I think the whole storage problem may not be such a big problem after all.
Do you really need to have a store of 11% of the city’s entire yearly energy usage? Like, 5 (almost 6!) entire weeks of energy? That seems ludicrously high to me.