The order from the Berkshire Hathaway Energy subsidiary will see SGRE supply 30 turbines to the unnamed Iowa project.
SGRE will manufacture 25 2.625MW turbines, with 120-metre rotors and five 2.3MW turbines with 108-metre rotors.
The deal also includes a five-year servicing agreement and the option to add a further five 2.625MW turbines, bring the potential total to 90MW.
SGRE will supply the nacelles and hubs from its Kansas facility.
The 2GW project had to-date been solely supplied by rival Vestas.
In 2016, the Danish manufacturer signed a conditional agreement with MidAmerican to "supply up to 1,000 V110 2MW turbines" to the project cluster in Iowa.
MidAmerican told Windpower Monthly Vestas was "the primary – but not exclusive – Wind XI turbine supplier".
A SGRE spokeswoman added: "This project is the only project with MidAmerican we can confirm right now."
At the end of March, Vestas announced the latest installment of its agreement with MidAmerican, a 92MW order.
A spokesman for th Danish manufacturer said:"Vestas’ original agreement remains in place and as announced, we expect to supply the vast majority of the turbines on the up to 2,000MW Wind XI project.
"Since our original order announcement of 100% exclusivity on PTC components for the project, we’ve announced hundreds of MW"s of orders towards the project.
"Vestas strongly considers that any other announced projects do not threaten our existing relationship and deals with MidAmerican."