Opinion: Edison's Revenge

Computerworld - Nikola Tesla must be rolling over in his grave. More than 100 years ago, he invented the alternating current network, which trumped Thomas Edisons direct current design to become the standard for electric power distribution networks. AC won because it was more practical. It was the more efficient and economical way to transmit power over long distances. Now the debate has risen anew, and passions are again running high. But this time, the battleground is over which is most energy efficient  and practical  as the distribution network for increasingly power-constrained data centers.

Edison may finally have his revenge. Or will he?

Youll find people who are religiously convinced in both directions, says John Pflueger, technology strategist at Dell and a board director at The Green Grid consortium. Many of those debates are raging within companies that are building new data center equipment, and The Green Grid is at the center. It launched a power distribution options study, due by years end, which is investigating seven alternatives. Three of those specify DC voltages.

IT equipment power supplies convert incoming AC power to the various DC voltages the subcomponents require. While some equipment also accepts DC input power, most data centers distribute 208-volt AC out to the racks. At least 10% of the AC power coming into data centers is lost to AC/DC and DC/AC conversion inefficiencies before it reaches the IT equipment. Every conversion step is maybe 90% efficient on a good day, says HP senior technologist and Green Grid board director Roger Tipley. That wasted energy creates heat that must be removed, increasing air conditioning loads.

DC returned to the forefront with the 2006 release of a paper by Lawrence Berkeley National Laboratory researcher William Tschudi. It showed a 20% overall efficiency gain in the data center by moving to a 380-volt DC power distribution scheme. Distributing DC would be relatively easy, Tschudi says.

That has some IT executives excited. Were studying it for a new data center were looking at building in the next two and a half years, says Bob Culver, senior vice president and manager of technology information group facilities at Wells Fargo. Joseph Hedgecock, senior vice president and head of platform and data centers at Lehman Brothers, says he is also taking a hard look at DC.

Theres a lot of buzz, and a lot of interest in using DC power in the data center, says Peter Gross, CEO at EYP Mission Critical Facilities, which designs data centers.