While Facebook might have won praise from locals with its construction of a data center in Prineville, Oregon, it has sparked the ire of the environmental activists at Greenpeace.

Yesterday, Greenpeace posted on its blog a letter from its director to Facebook CEO Mark Zuckerberg in which the environmental organization took the social networking company to task for the energy consumption and the energy source for the new Prineville data center. The facility will be powered by “dirty coal-fired electricity from PacificCorp, which runs an electricity mix that is disproportionately powered by coal, the largest source of global warming pollution,” and as Facebook has announced that the data center will be double the size initially planned, Greenpeace objects to this doubling of the demand for “dirty coal energy.”

According to Greenpeace, at current growth rates data centers and telecommunication networks will consume about 1,963 billion kilowatts hours of electricity in 2020 – more than triple their current consumption and more than the current electricity consumption of France, Germany, Canada and Brazil combined. Greenpeace says that over 500,000 people have joined the organization’s initiative calling for Facebook to “unfriend coal.”

Responding in the comments to the Greenpeace blog post, a Barry Schnitt, Director of Policy Communications for Facebook, touted the energy efficiency of the new data center, pointing out that while the industry average for Power Usage Effectiveness (PUE) ranges from 1.6 to 2 that the Prineville data center will have a PUE of 1.15. And Facebook. Schnitt suggested that there “just isn’t a perfect solution yet” to the energy problems associated with data centers, noting the percentage of coal energy tapped by Greenpeace’s own data center in Virginia.

Greenpeace responded on its blog today, agreeing that arguing that companies like Facebook are far from powerless to make a difference in the way in which energy consumption and sources operate. WIth being such massive consumers of energy, Greenpeace contends, Facebook can demand cleaner energy from its supplier. And Greenpeace pointed to the efforts by other Internet companies, namely Google and Yahoo in developing more energy efficient data centers.

While the tit-for-tat responses between Facebook and Greenpeace continue, it’s perhaps no coincidence then that Google updated its research blog yesterday with a post about the work the company is doing to develop “energy proportional data centers.”