Data centers also need cooling, since all that electricity going to and through IT gear eventually turns into heat. Typically, this cooling requires yet more electrical power. One measure of a data center's power efficiency is its PUE -- Power Usage Effectiveness -- which is the ratio of total power consumed by the facility for IT, cooling, lighting, etc., divided by the power consumed by IT gear. The best PUE is as close as possible to 1.0; PUE ratings of 2.0 are, sadly, all too typical.

"You want to be in a cool dry geography with cheap power, like parts of the Pacific NorthWest. For example, . Or in a very dry place, where you can get very efficient evaporative cooling," says Rich Fichera, VP and Principal Analyst, Infrastructure and Operations Group, Forrester Research.

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Companies like Apple, Google and Microsoft, along with data center hosting companies, have been sussing out sites that meet affordable power and cooling criteria (along with not being prone to earthquakes or , available and affordable real estate, good network connectivity, and good places to eat lunch).

Google, with an estimated 900,000 servers, dedicates to data center efficiency and other best practices, like, where and when possible, using evaporative cooling to minimize how often energy-hogging "chillers" run (When in use, chillers "can consume many times more power than the rest of the cooling system combined"). Evaporative cooling still requires power -- but much less. And Google's new facility in Hamina, Finland, "utilizes sea water to provide chiller-less cooling." (.) According to the company, "Google-designed data centers use about half the energy of a typical data center."