They join Google in choosing wind for the power-hungry facilities, which house IT equipment for computing, networking and data storage, as well as infrastructure for electricity and cooling.
On 13 November, Facebook said that its massive new data centre in Altoona, Iowa, which opens in early 2015, will be supplied by 100% wind power.
Facebook is not disclosing details but is known to have started developing a nearby wind project in Wellsburg with RPM Access. Facebook later "transferred" its rights to the 139MW project to MidAmerican Energy, part of Warren Buffett's Berkshire Hathaway.
Speaking about the structure of the deal, Vincent Van Son, data centre energy manager at Faceboook, said the social media company is matching the data centre's energy consumption with RECs generated from the wind project.
Facebook said that Iowa's plentiful wind power influenced the siting of the $1 billion project, the company's fourth data centre. "Wind is abundant in Iowa, and this makes wind energy far more cost-competitive than solar power," said Van Son. "Wind turbines also minimise the disruption to existing farmland since they have a smaller physical footprint."
Asked whether Facebook would invest equity in a wind farm, Van Son said that the company will continue to evaluate this option. Facebook's total energy use in data centres in 2012 was about 678,000MWh — up from 510,000MWh in 2011— whereas its office space and other facilities used only 27,000MWh.
In a different type of deal, Microsoft announced a week earlier that it had signed a 20-year power purchase agreement with RES Americas for all the output from the 100MW Keechi wind project, to be completed near Jacksboro in Texas in 2015. The electricity, partly funded by the company's own internal carbon fee, is for a Microsoft data centre in San Antonio.
Speaking about the deal, Josh Henretig, Microsoft's director of environmental sustainability, said: "The economics of wind energy have been improving over the last several years, with higher turbine efficiency and lower development costs, such that many wind projects are delivering power to the grid at parity with fossil fuels. This makes wind a smart choice."
On the challenges of buying wind, he said: "In most power markets generators are typically not able to contract directly with consumers... Microsoft's purchase agreement for the Keechi wind project, which includes all of the [RECs] associated with the project, is an approach that we believe works well within the current regulatory environment."
But the undisputed frontrunner for data-centre purchases of wind is Google, with five contracts so far for 574MW of wind energy in Iowa, Oklahoma, Texas and Sweden. It has invested $75 million in equity in RPM Access' Rippey wind farm in Iowa, where it already has a "hyper-scale" data centre.
Electricity used by data centres worldwide increased by about 56% from 2005 to 2010, while in the US it increased by about 36%, according to research by Jon Koomey, a professor at Stanford University.
Data centres now account for about 1-2% of the US's electricity consumption, says the non-profit Business for Social Responsibility (BSR). BSR is partnering with leading technology companies — such as Facebook, eBay, HP, Adobe and Symantec — on the Future of Internet Power project. The aim is to cut the climate impact of data centres, including by using renewable energy.
Data centres have a fairly constant demand for electricity because they are so optimised for efficiency and because their reach is often global, said BSR's Corinna Kester. Any source of renewable energy chosen for a data centre must typically be able to be expanded easily, reliable and — above all — low cost, she said.