MTechnology, a research firm that runs probabilistic risk assessment analyses of electric power sources, has released a study finding that flywheel-based uninterruptible power supply (UPS) systems are more reliable than the more common battery-based UPS during short outages of 10 seconds or less.

The study was paid for by Active Power, a flywheel-based UPS company, so you can take the conclusions for what you think they’re worth. Martin Olsen, the product manager and development director at Active Power, said that they “made it very clear that (MTechnology) would be doing the study, and to make it as objective as possible. That’s what they do for a living.”

Flywheel-based UPS systems have gained some traction in data centers as an alternative or complement to battery-based UPS. Terremark, a large data center colocation company, just recently installed flywheels instead of batteries at a new campus in Virginia. How it works is the primary utility power gets the mechanical flywheel spinning. When the utility power cuts out, inertia keeps the flywheel spinning at thousands of rotations per minute. That rotation is harnessed into power that can support the data center for short periods of time until either the utility power returns or the switch is made to backup generators.

The MTechnology study compared a flywheel UPS to double-conversion battery UPS and found that the flywheel was almost seven times more reliable than the battery UPS during short outages (10 seconds or less). During longer outages, failure rates were about the same.