No, superconductor. Effectively an electronic version of the flywheel.
There is a company in the United States that has been making these for almost 20 years now, they are used for ride-through in hospitals and for windfarm output stabilization.
Not really, I've seen these units in the middle of the mountains sitting right next to a windfarm. About as inaccessible as it gets and yet they were there and humming along. Note that there is plenty of energy available for the refrigeration and that those units run for years unattended. Occasionally you need to top off the refrigeration gear but that's once every two years or so, a bit more involved than your average HVAC setup but not that much more involved.
There is a company in the United States that has been making these for almost 20 years now, they are used for ride-through in hospitals and for windfarm output stabilization.
https://en.wikipedia.org/wiki/Superconducting_magnetic_energ...
https://www.amsc.com/gridtec/renewable-interconnectivity-sol...
Enjoy the read. It's interesting stuff.