What Google has done over the last decade, with relatively little fanfare, is participate in a number of large-scale deals with renewable producers, typically guaranteeing to buy the energy they produce with their wind turbines and solar cells. With those guarantees, wind companies can obtain bank financing to build more turbines.

The power created by the renewables is plugged into the utility grid, so that Google’s usage presents no net consumption of fossil fuels and the pool of electricity gets a relatively larger share of renewable sources.

http://mobile.nytimes.com/2016/12/06/technology/google-says-it-will-run-entirely-on-renewable-energy-in-2017.html