SAN FRANCISCO Pacific Gas & Electric Co. announced plans Thursday to buy natural gas generated from cow manure on California dairy farms. PG&E officials said the utility signed a deal with Microgy Inc., a subsidiary of Portsmouth, N.H.-based Environmental Power Corp., to buy enough biomethane to power an estimated 50,000 homes. The agreement represents the PG&E's first purchase of natural gas generated from cow patties. Manure-derived methane could make up a larger share of the San Francisco-based utility's electricity supply if the pilot project is successful, said spokeswoman Darlene Chiu. The deal could help increase the percentage of PG&E's electricity...