Server farms are expensive, but what's many times more expensive than the cost of all the hardware is the cost of keeping the place from incinerating itself with waste heat. Most farms rely on complex air conditioning systems, but Facebook has found a place where all it'll have to do is open a window: the Arctic.
Facebook's newest server farm (and it's first one outside of the United States) is going to be built in Luleå, up in northern Sweden. At 65 degrees of latitude, Luleå is just as close to the pole as Siberia, Greenland and most of Alaska, although technically, it's a few tens of miles south of the Arctic Circle itself. The average temperature up there is a whopping 35 degrees Fahrenheit, which is the perfect environment for a giant data center. Instead of having to pay a bunch of money for energy-hungry air conditioners, all Facebook is going to do is (more or less) open all the windows and turn on some fans.
This is not going to be some sort of piddly little exploratory project for Facebook. They'll be building three gigantic server halls, covering an area equivalent to 11 football fields. Even without having to pay for the additional A/C, the air cooling system is still going to cost about $75 million a year. The other appeal of northern Sweden, though, is cheap hydro power: the Luleå river produces twice as much electricity as the Hoover Dam.
Cold air may be cheap in the Arctic, but once a server farm sucks up a bunch of it, that cold air turns into hot air. Then it gets blown back out into the Arctic, which instantly gets a little less Arctic-y. 'Course, there's more than enough cold air to go around, but it's still just a little something that the Swedes should keep in mind, lest the environmental effects harm the indigenous moose and lucrative gummy fish industry.