Fossil fuels have been the prime mover of industrial life for some 200 years. The burning of coal and oil have saved inestimable amounts of time and labor while substantially raising living standards around the world. But many scientists now say the use of fossil fuels, which account for 85 percent of U.S. energy use, contributes to global warming and could ultimately threaten the planet's future. That concern, coupled with America's growing dependence on insecure fuel sources, has sparked new interest in alternatives. Unlike in the 1970s, however, this time renewable energy may be more than just a fad. Technological advancements have made the economics of wind and solar power much more competitive. Moreover, public utilities are beginning to consider the environmental costs of cheap fossil fuels.