Pattern bought the capacity from its development parent company Pattern Energy LP after the project's construction was completed and commissioned.
Panhandle I is located in Carson County, 48 kilometres from Amarillo in north Texas. It uses 118 GE 1.85MW turbines.
The American utility company said the deal was the second acquisition from Pattern LP since its IPO in February 2013.
The project is using Texas' new competitive renewable energy zone (CREZ) transmission infrastructure, which connects to the state's main power grid operator, Electric Reliability Council of Texas (ERCOT).
Citigroup Energy has bought around 77% of the electricity produced by the project under a long-term hedge offtake agreement.