The social media giant will buy the power from Citigroup Energy, which is buying most of Shannon's power under a 13-year hedge contract.
Shannon, with an installed capacity of 204MW, is co-owned by Alterra Power of Vancouver and Starwood Energy of Connecticut.
Shannon is expected to be online in late 2015 or early 2016, said an Alterra spokesman.
The GE 1.7-103 turbines are on site and will be installed starting this week or next. Mortensen Construction, which has the EPC contract to build the project, began onsite construction in January.
Facebook has previously agreed to buy wind power for a data centre in Iowa from MidAmerican's 139MW Wellsburg project. The data centre opened in November.
Earlier in July, Facebook said it would seek to run half its operations with renewable energy by the end of 2018, and it eventually intends to reach 100 per cent.