"Because batteries are expensive"
Are they? It would only take 4000 copies of the Moss Landing Energy Storage Facility to store all the electricity we currently use in a day.
Some back of the napkin math says it would cost $2 Trillion, which is only double the amout we subsidized the fuel industry last year
Technically yes, but that's a bad idea: ocean environment is very unforgiving, and has more clouds than land has. It also has more (and more reliable) wind and fewer people complaining about the very large turbines, which is why it works for wind.
> Some back of the napkin math says it would cost $2 Trillion, which is only double the amout we subsidized the fuel industry last year
Napkin maths also says that a global power grid would be 10% of that price. By coincidence, it takes a cross section of almost exactly 1m^2 to make a 40,000 km long line have a resistance of 1 Ω.
Further investigation said that literally only China has that much spare capacity for aluminium production, but still.
That kind of scale of battery production is still needed for the cars, though.
It’s ultimately more about unit cost of power than total available power.