Learning that flywheels have an energy storage density competitive with batteries. There was once a bus that was powered entirely by a flywheel (it could only go 6 kms, but still). Trying to get my head around how this could all be true while national grids are still buying batteries for their load balancing.

The explanation turns out to be weird: Despite flywheels being so conceptually simple, despite being able to go 20 years without maintenance, batteries are significantly cheaper??


How could that be true? Good flywheels are kept in a vacuum, on magnetic bearings. I came across one that uses high temperature superconductor. Often, they're strengthened with carbon fiber (but why would that affect cost efficicacy? Why not just make a larger number of cheaper ones without the strengthening that can't spin as fast?).

I still can't believe this and I suspect it comes down to economies of scale or something annoying like that.

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