The Public Service Company of New Mexico (PNM) says shutting down part of the plant and installing more pollution controls on the remaining units would bring it into compliance as well as reduce carbon-dioxide and mercury emissions by as much as 50 percent.  FILLING THE VOID PNM wants to replace the lost electricity with a mix of coal from one of San Juan's other units, electricity generated by the Palo Verde nuclear plant in Arizona, a new natural gas-fired plant and more solar generating stations. Environmentalists and some consumer advocacy groups argue the plan doesn't do enough to wean the state's largest utility off fossil fuels and that ratepayers could be locked in to coal and nuclear power for years to come.  THE PORTFOLIO More than 60 percent of electricity generated by PNM in 2014 came from coal. Solar, wind and geothermal sources totaled just over 7 percent.