The Silver Lake power plant in Rochester, Minn., has four units from four to six decades old. Each can burn coal or natural gas, but the units are seldom run because electricity can be purchased for less off the regional power grid.

UnitMW*Year builtHours run, 2011

19.5194843

214195395

324196261

445196958

*1 megawatt (MW) equals 1 million watts.

Source: Rochester Public Utilities