Shopping online consumes far less energy than driving to the mall or downtown, and you won't suffer knife wounds trying to get onto for early specials, but it certainly could be a lot more efficient than it is.

In an average year, the top 40 retailers spend an estimated $110 million more on energy during than they should in preparing for Cyber Monday, the first workday after Thanksgiving that's been enshrined as the start of the online holiday shopping season, according to data center efficiency experts at Sentilla.

"The carbon impact of this power waste is approximately 727 million pounds of carbon dioxide. That's more CO2 than emitted by all of the round trip flights each year between SFO and JFK," says Joe Polastre, Sentilla's CTO and co-founder.

Every dollar of energy use that is avoided in a data center leads to $5 in savings in operational expenses, he added, citing IDC data. Thus, the top retailers are spending over a half a billion too much on operations during the year to gear up for Cyber Monday. That doesn't even count the extra servers and storage systems they buy. If you add in capital costs, the total comes to the billions.

The problem is that data centers still aren't optimized for efficiency as much as they could be. Data centers generally only use 15 percent to 20 percent of the capacity of their servers and other IT equipment. The level of computer utilization remains low to guard against sudden spikes in traffic.

Servers and storage systems, however, consume an inordinate amount of power when idling: the power drops only to about the 80 percent level, not to a deep sleep state of 10 percent or lower. Thus, you have a lot of equipment consuming energy while just waiting around for something to do.  Indeed, 83 percent of organizations don't even know how utilized their servers are, he added, citing IDC data again.

On Cyber Monday and during the holiday shopping season, utilization actually climbs, said Polastre. That should lead to lower energy consumption per workloads or transactions.

"We call it data center efficiency day," he said.

Unfortunately, to prepare for the season, these companies go on buying binges months before and eventually install 30 percent more equipment than they need.

Many companies are trying to ameliorate this problem through cloud computing strategies. Amazon, of course, sells its fallow capacity as cloud services and many companies have begun to adopt cloud applications for certain corporate functions. Still, many retailers remain reluctant to put all of their transactional and sales capabilities in the hand of a third party. Instead, they insulate themselves against worst-case scenarios by buying lots of equipment they could probably live without.

"Having the website go down is a lose-your-job sort of event," he said.

Sentilla, and competitors such as SynapSense, Federspiel Controls and Power Assure, all claim they can curb power consumption in data centers through better management of air conditioners and/or controlling the application loads on computers. (Sentilla examines power consumption with sensors and software and then helps craft a strategy to crank down the power, so they are kind of like a weather forecaster/life coach for servers.) Meanwhile, Calxeda (formerly Smooth-Stone), SeaMicro and others are developing hardware that will consume less energy in the first place.

Data centers in many ways are becoming the test beds for building management technologies, which in turn has made green IT one of the more exciting green markets these days ABB, Cisco, General Electric have all begun to invest in this area.