There is much today about the energy storage capacity of magnetic bearing Flywheels. One I read about was made of bamboo fibers and could be spun up to 90000 rpm at that time not even carbon fiber could take that speed. The article said when the wind stopped there was enough energy stored in the wheel to operate a large farm for a week. They did not give a clue what that meant in KW. To me this would be like having a large bomb near my home. All other materials failed and disintegrated. At much lower speeds. as a guess what do you think would happen if one of these failed at such speed?