The US Department Of Navy (DON) is to have a 210MW solar farm in Arizona.
It will power 14 Navy and Marine Corps bases.
The Mesquite Solar 3 project will have 650,000 panels which will provide a third of the energy needed to power the bases.
It will be developed by Sempra US Gas & Power and is expected to be completed by the end of 2016.
Secretary of the Navy Ray Mabus said DON estimates to save around $90 million (£57.6m) over the lifetime of the project.
He added: “The collaboration on Mesquite Solar 3 is a triumph of innovative problem solving and will help to increase the DON’s energy security by diversifying our power portfolio and improving energy efficiency.”
The agreement is claimed to be the largest purchase of renewable energy ever made by a federal entity.