From 1915 to 1970, an increasing number of new units were brought on line each period. A record of 73 units started up in the period of 1951–1960. With half as many new units (37) than 1951–1960, the 1971–1980 period had the biggest increase in capacity (3,379.7 megawatts). Nuclear power accounted for almost half of the capacity added that period. In the 1981–1990 period, energy from biomass contributed 3.5 megawatts capacity. Of the 368.3 megawatts capacity added in the 1991–2000 period, 3.0 megawatts were from wind power. In the 2001–2010 period, energy from natural gas contributed 1,075.5 megawatts capacity, coal contributed 809.4 megawatts, wind power contributed 292.592 megawatts, petroleum contributed 10.5 megawatts, landfill gas contributed 6.4 megawatts, biomass contributed 1.08 megawatts, and solar contributed 0.0524 megawatts. In the 2011–2012 period, energy from coal contributed 248.0 megawatts capacity and wind contributed 262.5 megawatts.
A Note About Nameplate Capacity
Summer capacity and winter capacity is sometimes greater than nameplate capacity. The nameplate gives the capacity rating of the generator when it operates at certain temperatures, pressures, and power factors. With some modifications and with some margins that are built into generators, it is possible to exceed its nameplate. It is not uncommon for a generator to exceed its nameplate. The nameplate is usually not replaced and, in this case, the summer and winter capacity is often much higher than the nameplate value. Normally, you expect summer and winter capacity to be below nameplate capacity and in most cases they are.