Combined cycle plants have recently received acceptance due to their improved efficiency. Combined cycle plants use direct or gear drives from gas turbines to turn electrical generators. The high temperature turbine exhaust gases are used to heat water boilers which produces steam that propels a second set of turbines. The difficulties at Three Mile Island and other nuclear power generation facilities are well known. Both economic and environmental factors have stopped nuclear power plant production in the U.S. for the foreseeable future.
Nuclear fusion has yet to be proved feasible.
Breeder reactors which produce plutonium are out of consideration in the United States. Hydroelectric power is clearly the world's most successful method of harnessing Nature for power production. However, virtually all feasible sites have been developed. At huge cost and after flooding vast areas in Egypt and China, the toll of new hydroelectric dams has been high. Green power systems such as wind, biomass, solar, and geothermal sources will continue to be used, but all are limited in both capacity and availability of acceptable sites.