Greenpeace released a report today on the "dirty energy" powering cloud data, and says that Apple is the worst environmental offender with 55.1 percent of its cloud energy coming from coal — but Apple and others have already raised concern over the group's methodology. Greenpeace says that information on the mix of energy used by cloud data facilities is hard to come by and that companies have been generally unwilling to provide it. So its methodology combines data from investor and media reports, a 2007 EPA electric power database, international statistics, and the most recently published data from local utilities on the general mix of energy sources. Critics say that Greenpeace's calculations lack appropriate data and consistency.

One particular target in the Greenpeace report is a new North Carolina data center from Apple, which received a LEED Platinum certification, and will host a 100-acre, 20-megawatt solar array and 5-megawatt fuel cell system. But Greenpeace does not use that information as the basis for its claims, instead opting for its own calculation of energy use based on reported investment data. The group estimates that there is 1-megawatt of power demand for every $15 million invested in a cloud facility, and with a reported investment of $1 billion, the North Carolina data center would use 100-megawatts of power. But as AllThingsD reports, Apple says that its data center will draw only 20-megawatts at full capacity, and that more than 60 percent of power for its North Carolina facility will come from renewable sources.

Greenpeace routinely targets high-profile tech companies with reports of their environmental practices as part of its advocacy efforts, and in this most recent report Apple is followed by others like HP, Facebook, Microsoft, Twitter, Amazon, and Google. As Greenpeace says that its analysis "does not attempt to represent itself as a comprehensive snapshot of how much clean energy is being consumed on a company-wide level," it seems that the report is in part an effort to prompt companies to release additional data on their energy consumption. Considering that Apple responded within hours of its release, we'd say that Greenpeace has already achieved the start of a conversation, but we'll have to wait and see if other fingered companies are willing to respond.