In April, Greenpeace released a for major tech companies' data centers. Microsoft received "C" ratings on energy transparency, energy efficiency, and renewables, and a "D" rating on infrastructure siting. Other companies, including Twitter and Amazon, fared worse, while Google and Yahoo earned higher marks.

But Apple, which was also criticized in the April report, at the time. Apple said that its Maiden, North Carolina, facility draws only one-fifth of the energy that Greenpeace claimed, and that 60 percent of its power will eventually come from a solar farm and a fuel-cell installation, which will both be the largest in the country.

Microsoft, in fairness, is now across all of its direct operations, including data centers, which means the company buys energy credits and carbon offsets to compensate for non-renewable energy uses. But Greenpeace is not placated. "Those tactics may be good for Microsoft's reputation, but they result in no less coal burned and no more renewable energy produced to power the Microsoft cloud," the group said in a statement.

Greenpeace is more impressed with Google, which has invested more than $900 million in renewable energy and recently to help power one of its data centers, and with Facebook, which on a renewable energy policy.