19. Green Mountain
Green Mountain, based in Norway, has several energy-efficient data centers, but DC1-Stavanger, an underground data center built in a former NATO ammo bunker, is an efficiency king.
The subterranean data center is powered by 100% renewable energy from its own triple-redundant hydroelectric grid, which gives it nearly 100% uptime along with being green.
Stavanger is also passively cooled using nearby fjords.
SEE: Green tech initiatives: Best practices and breakthroughs (free PDF) (TechRepublic)
Image: Green Mountain