The fortunes of renewable energy sources always have been tied to prices for conventional fuels. Wind, solar, biomass and other sources become more attractive as prices for fossil fuels rise and make the alternatives more competitive.

Yet, according to the PJM Interconnect - the power grid covering Pennsylvania, 12 other states and the District of Columbia - more than 1 gigawatt of electricity is produced by solar power across the grid even as natural gas from the Marcellus Shale drives down prices. A gigawatt is 1 billion watts, enough to power 800,000 homes.

According to energy expert John Hanger, solar, wind, biomass and hydroelectric sources have generated 40 gigawatts of power across the PJM grid since 2005 - the year that exploratory gas drilling began in the Marcellus Shale.

This year, another 64,000 megawatts of alternative energy is expected to be added to the grid, mostly from wind power.

The vast expansion is due to several factors. Solar-panel production costs have plummeted. States within the PJM grid have established energy portfolio standards requiring state governments to purchase an average of 20 percent of their power from alternative sources. Federal tax credits promote alternative sources.

Given the broad embrace of alternative sources, the Corbett administration and lawmakers should rethink their elimination of a state program that had helped to drive the expansion in solar power.

And federal lawmakers should renew the production tax credit for wind power, which otherwise would expire at the end of this year. It has helped to drive down the cost of wind power and to preserve and expand jobs in the industry.