The Alternative Energy Bill requires utilities to get 18 percent of their electricity from alternative energy sources by 2020. Utilities must get 8 percent of their electricity from so-called "Tier One" sources that include wind, solar and biomass.

The other 10 percent must come from "Tier Two" sources such as coal waste and traditional hydroelectric power.

Citizens for Pennsylvania's Future, an environmental public policy group based in Harrisburg, estimates the new law could reduce carbon dioxide emissions by 67 million tons, nitrogen oxide emissions by 59,000 tons and sulfur dioxide emissions by 589,000 tons during the next 15 years.

John Hanger, president of the public policy group, contends the bill also will create new jobs throughout the state. Wind turbines are expected to generate an estimated 3,600 megawatts of electricity - more than enough to supply the energy needs of 1 million new homes. The additional capacity should make Pennsylvania a major power exporter.

Environmentalists were chagrined that the coal waste provision was added. While plants that burn coal waste, or culm, must meet federal clean air standards, there are concerns about the toxic heavy metals that remain in the ash.

That issue requires monitoring, but this bill gives Pennsylvania a significant edge on green energy production.