_whiteCaps_ parent
Caterpillar provides some really neat small scale flywheel UPS - used in places like hospitals where it would be very bad to lose power. They last long enough for the diesel gennies to start up.
I saw these in the basement of a data center about 11-12 years ago. Most steampunk thing I've seen in real life.
Here's a bigger one at ASDEX (a fusion experiment):
I've worked on mine sites that use this as well.