But other experts point out that the high cost of real estate is causing many data centers to migrate to suburban or rural locations, where underground lines are a rarity.

"As the electricity arrives from the generating plant, I can tell you it's all going to be up in the air somewhere," Henkels' Pieper said.

Hypertect's Svenkeson recommended that data centers have two backup generators, or a "backup for their backup." But he says that due to new EPA emission requirements that went into effect at the start of this year, backup generators have both become pricier and harder to find. Peak 10's Biggs claimed that the amount of backorders at many manufacturers is so heavy that it would take a year for a generator ordered today to be delivered.

Looking forward, underground power may slowly become more practical as the technology to cool and insulate the cables improves.

One plastic insulator, cross-linked polyethylene (XLPE), allows underground transmission lines nowadays to carry up to 345,000 volts, said Pieper. That amount of voltage was first carried underground in a southern Connecticut project completed in October 2006. And technologists in the lab are working on superconductors that would use liquid nitrogen to cool conductive wires to allow electricity to travel over long distances with no power loss.