FLYWHEEL Energy Storage Systems

A friend told me just yesterday that the Wall Street Journal had made reference to a Flywheel energy storage system was being worked on by a Japanese power company.

http://www.energystorageforum.com/e...mpany-develops-flywheel-system-energy-storage

This Wikipedia reference is also very interesting:
https://en.wikipedia.org/wiki/Flywheel_energy_storage

Wow, I found myself again,...via google.

I had forgotten about this subject thread I started a number of years ago,..then a friend brought up this subject of energy storage recently,
http://www.bbc.com/future/story/20190327-the-tiny-islands-leading-the-way-in-hydrogen-power

I was never that 'hot' on the idea of hydrogen storage. It cost too much energy to make hydrogen,...and I remember Germany's problem with it when they couldn't get helium from us for their airships.

It made me think back to this older idea of mechanical energy storage,...maybe still viable for ground based power plants