> Electrical grids don't store energy. If you wanted to store just 10% of the U.S. electrical generation from summer to winter using lithium-ion batteries, it would cost roughly $42 trillion dollars. Yes, trillion.

Do you mean 10% of the generation on a typical summer day? Or 10% of the generation of an entire summer?

The problem with this kind of calculation is that battery technology (and cost) is very much a moving target.

LFP would probably be the better choice today. It's cheaper, safer, and can handle far more load cycles. That comes at a cost of a lower energy density, but that hardly matters for utility scale batteries. Tesla's megapacks use LFP already - https://cleantechnica.com/2021/05/11/tesla-transitions-to-lf....

Like you say, there are many other energy storage options like pumped hydro, compressed air, etc. My personal favorite is the train full of concrete that goes up and down a hill (https://interestingengineering.com/concrete-gravity-trains-m...).