And flywheels! That’s what my startup is working on.

Came here to ask: why store energy in chemical batteries rather than gravity batteries (like pumping water up a mountain)? I know this is done (like here: https://www.tva.com/energy/our-power-system/hydroelectric/ra...)

Batteries are generally better for short term storage, aka daily usage. Pumped hydro is generally better for long term storage. We need both, but we can generally efficiently get to 70-90% carbon-free electricity without long term storage so we haven't need much long term storage yet.

> Pumped hydro is generally better for long term storage

Up to a point. Very long term storage is another thing again.

This twitter/X post has a very nice animated graphic of the predicted evolution of storage technologies over time (from 2020 to 2030), plotted against two attributes: duration of discharge, and # of cycles per year.

https://twitter.com/iain_staffell/status/1722544993179504965

Li-ion batteries and hydrogen are expanding the areas where they would dominate; pumped hydro is shrinking. Compressed air is getting squeezed out (no pun intended).

Water and increased physical space aren't universally available, which can raise cost.

PHES consumes surprisingly little water, even in a desert. It's an order of magnitude less than evaporated by a thermal power plant of the same energy throughput.

Energy density on chemical batteries is orders of magnitude higher than e.g. gravity batteries. Also you don't need to rewire a mountain.