This page offers some insight.
Electric cooperatives are nonprofit, independent, free enterprise businesses.
They sell electricity in towns, suburbs and rural areas in all 46 counties in the state. They share ownership of some power plants with other utilities and buy wholesale power from several sources as well. The Relationship Simply put, their relationships are contractual. Fifteen of those cooperatives provide power to end-use customers. Saluda River also generates some power through its joint ownership of the Catawba Nuclear Plant in York County.