Pentadyne Power, a Chatsworth, Calif.-based developer of flywheel energy storage systems, has just closed a $22 million financing round, led by return investors. The company didn’t disclose the identity of its backers though it has previously received support from Rustic Canyon Partners, Loudwater Investment Partners, Nth Power, Energy Innovation Portfolio and others.

It will use the proceeds to expand its operations overseas and to increase its sales of existing and new systems. Flywheel systems, an alternative to conventional battery-based uninterruptible power supply (UPS) systems, store energy kinetically, rather than chemically, which makes them lighter, more durable and environmentally friendly. Data centers use flywheels in case of a temporary power outage until diesel generators are able to kick in.

In the past, flywheels have suffered from low efficiency and high standby energy consumption, making them a less than ideal choice for large manufacturers. But Pentadyne claims to have largely circumvented this problem by eschewing the use of heavy mechanical bearings, which minimizes drag and maintenance costs and results in annual energy savings of $3,000 or more. Its flywheels also produce much less heat, below 1,000 British thermal units (BTU) per hour (compared to a typical average of 8,500 BTU per hour), which further reduces operational costs.

The company expects to make $18 million in total revenues this year and has previously taken $56 million in funding, including $14 million from Loudwater Investment Partners last September.