The best short to medium term grid storage battery is pumped storage. 90% efficiency. Price per MWh of about 1/3 of the cheapest lithium battery. Largest one is

The best short to medium term grid storage battery is pumped storage. 90% efficiency. Price per MWh of about 1/3 of the cheapest lithium battery. Largest one is 350GWh. The geography to build these things is extremely common - there's very little shortage of up. The best long term grid storage is probably still electrolyzed hydrogen pumped into a cavern underground. ~50% round trip efficiency but very high energy density at relatively low cost.