Apple on Wednesday contested claims from Greenpeace that its North Carolina data centre will be mostly coal powered, as part of the environmental organisation's critical look at its data centers.
Apple is one of several companies given poor marks in a new Greenpeace report released on Tuesday called "How Clean Is Your Cloud," which analysed electricity consumption by data centres.
Greenpeace criticised Apple's Maiden, North Carolina, facility, alleging that renewable energy sources such as fuel cells and solar arrays will only generate 10 percent of its electricity needs, with the rest generated by coal.
Apple contested that claim, saying 60 percent of the power will be eventually delivered on-site from a solar farm and fuel-cell installation "which will each be the largest in the country."
"We believe this industry-leading project will make Maiden the greenest data center ever built," it added.
Greenpeace also made an error when estimating the facility's power consumption, Apple said. At full capacity, the facility will draw about 20 megawatts of electricity, not the 100 megawatts that Greenpeace alleged, according to an Apple spokeswoman.
In its report, Greenpeace charged that Apple is "finding itself behind other companies such as Facebook and Google" because of a lack of transparency and commitment to renewable energy.
Facebook was noted for its Swedish data centre, powered entirely by renewable energy, and Google received high marks for being more transparent about its energy use and committing to use renewable energy.
Amazon and Microsoft however received low marks from Greenpeace, which said both "rely heavily on dirty energy to power their clouds."
Microsoft is expanding its data centre operations in Virginia, which is heavily reliant on coal and nuclear energy. The majority of servers for Amazon Web Services are in northern Virginia, where coal is mostly used, Greenpeace said.
Twitter received the lowest mark, an "F," for failing to set goals for energy emissions and the same mark for not sharing information on its leased Sacramento data center site, Greenpeace said.
The companies could not be immediately reached for comment.