"You could walk across a data center and see half-empty racks, and yet you're out of power," he says.

Besides using old equipment, data centers often waste energy by over-provisioning power, giving a particular system more electricity than it really needs, according to Linesch.

HP this month new technologies that measure and control power and cooling systems, while placing limits on power used. The idea is to identify how much power is needed to run each server and set limits based on the actual usage.

More intelligent use of water for cooling systems also is important, Kosik says. For some large data centers, getting enough water from public sources is challenging, so they build their own wells.

"We're working on projects lately where they have the power, but they don't have the water," Kosik says. "We're looking at on-site wells and running new water and sanitary lines that are basically big enough for a small city."