An article in a recent issue of IEEE Spectrum reported that today's data center commonly requires 20MW of power while those of the dot-com era consumed 1MW to 2MW. This is because today's largest data center houses many tens of thousands of servers, with some passing the 100,000-server mark.
The article goes on to say that with electricity prices going up, it's extremely expensive to power and cool so much equipment. Market research firm IDC estimates that within the next six years, the companies operating data centers will spend more money per year on energy than on equipment.
Also, the article says that the management consulting firm McKinsey & Co. has reported that the world's 44 million servers consume one-half percent of all electricity and produce two-tenths percent of all carbon dioxide emissions, or 80 megatons per year, approaching the emissions of entire countries like Argentina or the Netherlands.
Finally, the article says that since energy flows through transformers, converting MV AC power to 120V or 208V for server racks, the data center loses eight to nine percent of its energy. Also, each server needs to make an AC-to-DC conversion for its processors, memory, storage, which generates additional losses. These losses have led some experts to propose distributing DC power throughout the data center, which they say can cut losses by five to 20 percent.
(Source: http://enews.penton.com/enews/powerquality/power_quality_news_beat/2009_february_9_february/display#a090206_2)