Here's another startup that's been starting up for a while now. Active Power was founded in 1992 and provides what it calls flywheel-based UPS systems.

While Active Power calls it a UPS, the system is not the sort that can supply power for hours in the event of a power outage. Instead, it uses a spinning flywheel to provide power through transient spikes and dips, and can also supply enough power to allow generators to start up. Generators usually take just a few seconds to come on line.

The company just completed a private stock placement that raised $14 million. The funds will be used to "grow the business," according to its press release.

There's no doubt that the rush for everything "green" has rekindled interest in Active Power. Since the system requires no batteries -- with their environmentally unfriendly lead acid makeup -- there's substantial benefit for the environment. Of course, the only data centers that could benefit from the system must include generator backup. Active Power also sells systems with generators fully integrated.

Active Power says it has 1,600 flywheel systems in place and cites health care, data centers, and government applications among its product's usage.