 Renewable energy and the future of coal-fired power plants are looming battles for the state of South Dakota. Minnesota regulators have set 2040 as the year all electric utilities will be required to produce only carbon-free energy. The dispute includes the Big Stone South Dakota power plant near Millbank, which isn't slated for retirement until 2046. On the federal level, South Dakota joined 23 other states in fighting new rules affecting the coal industry.