The Pennsylvania Public Utility Commission yesterday approved a Peco Energy Co. proposal to buy solar-energy credits for 10 years, which officials expect will substantially boost the nascent market for renewable energy.

The ruling allows the Philadelphia utility to begin buying alternative-energy credits to comply with a law that forces utilities to derive a gradually increasing portion of their power from renewable-energy sources.

PUC chairman James H. Cawley commended Peco "for taking the initiative to kick-start the process." The state's Alternative Energy Portfolio Standards Act requires electrical utilities to buy 18 percent of their power from alternative-energy sources by 2020.

The market for solar alternative-energy credits has been "very thin and very illiquid" because the laws requiring utilities to buy solar power are only starting to kick in, according to Mike Freeman, senior originator of Exelon Generation Co. L.L.C., the wholesale power arm of Peco's parent company, Exelon Corp.

Peco's planned purchase of 80,000 credits over 10 years - each credit represents one megawatt-hour of power, or about as much as a residential customer would consume in a summer - should provide a strong signal to solar builders about the value of their projects, which will assist long-term financing.

"This is a fairly significant event in the solar world," Freeman said of the decision.

Renewable-energy credits are sold by electric generators for every one megawatt-hour of renewable power they produce, apart from the income they derive from selling the electricity itself.

Peco said it would competitively purchase the credits through requests for proposals. The energy must be generated within the area served by the regional grid, PJM Interconnection L.L.C., which covers parts of 13 states.

Though the market for the credits is not fully established, the PUC estimates their value at $230 each - and some experts say the price will probably exceed $300 each. That means Peco's investment could exceed $24 million.

Contact staff writer Andrew Maykuth at 215-854-2947 or amaykuth@phillynews.com.