In a new report entitled "How Clean is Your Cloud?" Greenpeace has accused tech companies of leaving a trail of pollution from "dirty energy" sources and failing to make clean energy a priority.

Cloud computing has become very popular, as it allows users to store and access data, programs and other information on remote servers, thus saving computing power. On the other hand, tech companies need massive data centers to do this, and such data centers suck great amounts of energy. Greenpeace's report on Tuesday, April 17, singles out three tech companies offering cloud computing services. The agency has called on the companies for using coal and other fossil fuel energy for their data centers.

"Three of the largest IT companies building their business around the cloud - Amazon, Apple and Microsoft - are all rapidly expanding without adequate regard to source of electricity, and rely heavily on dirty energy to power their clouds," wrote Gary Cook, senior IT policy analyst at Greenpeace International and lead author of the report.

Low Grades for Amazon, Apple and Microsoft

The report graded companies in four categories. Amazon received an "F" in energy transparence, infrastructure siting, and renewables and advocacy, and a "D" in energy efficiency & GHG mitigation. Apple got a "D" in energy transparence, energy efficiency & GHG mitigation, and renewable and advocacy, and an "F" in infrastructure siting. Microsoft got a "C" in all categories but infrastructure siting, where it received a "D." GHG stands for global greenhouse gas emissions. Besides Amazon, the only company to score worse than Apple was Twitter, with two "Fs" and two "Ds." Google got the highest scores.

According to the report, Yahoo and Google "continue to lead the sector in prioritizing access to renewable energy in their cloud expansion, and both have been more than active in supporting policies to drive greater renewable energy investment."

Apple Dismisses Greenpeace Estimates as Incorrect

A day after the Greenpeace report was published, Apple countered back and claimed Greenpeace's estimates are incorrect. Apple said its new data center currently under construction in North Carolina will need about 20 megawatts at full capacity, which is only one-fifth of the 100 megawatts Greenpeace had estimated. Greenpeace reportedly made its estimate for the power Apple's N.C. plant would use based in the size of the facility, as well as the size of the investment. The report notes that Apple has dismissed the estimates as incorrect, but did not provide a more accurate number.

In a statement issued in response to the Greenpeace report, Apple for the first time disclosed the expected power usage at its new facility. In addition, Apple also notes that its Maiden, North Carolina facility will have a solar array and run fuel cells powered by biogas or methane captured from landfills, or other organic resources.

'The Greenest Data Center Ever Built'

"We believe this industry-leading project will make Maiden the greenest data center ever built, and it will be joined next year by our new facility in Oregon running on 100% renewable energy," stated Apple.

According to the tech giant, its Maiden, N.C. plant will drive 4.8 megawatts' worth of power from fuel cells, and the solar installation is estimated to be 20 megawatts. Apple further estimates that such on-site renewable-energy power sources will supply roughly 60 percent of its power. However, Greenpeace's Gary Cook questioned how would Apple's 500,000-square-foot facility manage to consume just 20 megawatts, and called for even more transparency from Apple.

(reported by Alexandra Burlacu, edited by Dave Clark)