A Bakersfield company has signed a 15-year contract with Pacific Gas and Electric Co. to sell "biomass" energy produced by burning local tree trimmings and other waste wood, the utility announced Monday.

PG&E said the project will produce 327,624 megawatt hours of electricity annually, enough to power 47,000 average homes.

A partner at Mt. Poso Cogeneration Co. said the deal would not take effect until the company completes a $50 million conversion from using mostly coal and petroleum coke to running on 100 percent biomass fuel. He said the project is expected to be finished in 2011.

Mt. Poso, which also produces oil, has sold mainly coal-based power to PG&E since 1989; it uses the byproduct steam to enhance its oil production operations in a commonly used process called steam injection.

PG&E, spurred by the state's recent emphasis on non-petroleum-based energy, has signed contracts to purchase more than 20 percent of its future electric power from biomass and other renewable energy sources.

The utility would pay Mt. Poso more for the biomass energy than it pays now for the electricity created from coal and petcoke. PG&E declined to state how much more.

The partner at Mt. Poso, Michael Hawkins, said wood biomass burns more cleanly than coal or petcoke, and that if left to decompose, it produces methane, which is more noxious than carbon dioxide.