Google has entered into a power purchase agreement with a wind farm to buy the power (more).
Essentially, Google Energy acts as a quasi-utility, signing long-term contracts for electricity. In this case, it has committed to a 20-year contract to buy the electricity generated by a 100.8-megawatt wind farm called Minco II that NextEra will build in Oklahoma, where a new Google data center is set to go online later this year.