The future of the most expensive fossil-fuel power plant built in the U.S. is facing new pressures after a Mississippi utility backed out of its commitment to the clean-coal project. South Mississippi Electric Power Association, which furnishes power to smaller utilities in the state, dropped its plan to buy a $600 million, 15% stake in the project spearheaded by Atlanta-based Southern Co. SO -0.35 % , citing construction delays. Southern, in turn, notified state regulators that it may have to raise electricity rates for Mississippi power customers by 41%, or $37 a month for the typical household, to pay for the project. South Mississippi Electric Power’s move deals a […]