alt Hacker Newscan you explain the economics of that to me, because it doesn't track my understanding.
Are you just talking about total capacity dominated breakeven? The economics of both want daily cycles. Water has a more favorable power/$ scaling curve for storage if you have a site.
Any sort of seasonal storage is horrendously expensive and completely infeasible using economics alone. It's really only a concern once our power grid is 98%-99% carbon-neutral and we want to get it to 100%.
A battery storage facility has watts and watt-hours roughly equivalent. A typical storage battery is around "1C" -- it takes about one hour to fully charge or discharge. The limiting factor on the build price is the MWh -- if you keep the power the same but double the storage the price of the plant still roughly doubles.
A typical daily storage facility wants around 4C, so that coupling between power and energy for batteries is not a significant drawback.
Seasonal storage is not coupled in this way. You increase MWh by increasing the size of your reservoirs. You increase MW by increasing the number of pumps/turbines. MWh is usually a lot cheaper than MW. A typical pumped storage facility today has MWh only being 10-20X the MW which means they're tuned for daily-ish usage (see top line). One tuned for seasonal usage would have that ratio >> 100.