Facebook today turned on the lights at its data center in Luleå, Sweden.

The building sits on the edge of the Arctic Circle, and boasts(Opens in a new window) equipment powered by locally generated hydro-electric energy.

“Not only is it 100 percent renewable,” Facebook said, “but the supply is also so reliable that we have been able to reduce the number of backup generators required at the site by more than 70 percent.”

Additionally, the social network is putting the chilly Nordic air to good use, cooling the thousands of servers that store users’ data; any excess heat, the company said, will be used to keep the Facebook office warm.

“Nearly all the technology in the facility, from the servers to the power distribution systems, is based on Open Compute Project designs,” Facebook said. “This Facebook-founded initiative encourages the development of ‘vanity-free’ hardware designs that are highly efficient and leave out unnecessary bits of metal and plastic. These designs are then shared with the broader community, so anyone can use or improve them.”

Facebook first announced plans for the Swedish data center in Oct. 2011, its first outside the U.S.

Greenpeace, which has tangled with Facebook in the past on environmental issues, praised Facebook for opening what it said is Facebook’s first coal-free data center, but took issue with the social network’s choice of provider.

“Given the choice of energy providers for Luleå, Facebook has not immediately opted for a 100 percent renewable energy provider, instead choosing the giant utility Vattenfall, which still invests primarily in non-renewable energy,” Greenpeace Senior IT Analyst Gary Cook said in a statement.

“As Facebook continues to grow its facility in Sweden, we expect it will seek to expand its access to renewable sources of electricity,” Cook said.

Facebook did not immediately respond to a request for comment.

The social network has a number of data centers here in the U.S. to help it handle traffic for its 1.1 billion members. In April, it confirmed plans for a data center in Altoona, Iowa, which should open next year. In February, meanwhile, there was a report that Facebook was gearing up to launch three new “cold storage” data centers in Prineville, Ore. to store older and rarely viewed images.