Potrero Generating Station

The Potrero Generating Station, most recently owned by Atlanta energy company Mirant (now GenOn Energy) and located at Potrero Point in San Francisco, California, is a large power plant, on a 23-acre site, which burns diesel and natural gas. Its main source of power is a 206-megawatt natural gas steam turbine known as Unit 3 that provides baseload power. In cases of excess usage, Unit 3 is bolstered by a trio of 52-megawatt diesel peak power engines, capable of being activated within four minutes and peaked in ten, to provide enough potential energy to meet roughly a third of San Francisco’s needs during peak times.

As a power plant in the U.S. whose generators were all built before 1980, the Potrero Generating Station may contain a large amount of asbestos within its facilities. It was used to protect employees and facility infrastructure by providing insulation from the extreme temperatures generated by the machines in the plant.

The Potrero station is located at a site which first belonged to San Francisco Gas Light, which later grew into the Pacific Gas & Electric Company. In 1965, PG&E built Unit 3, and in 1976 the three diesel peaking units were built. Unit 3 consists of an eight-story boiler powered by natural gas that produces superheated steam, which turns the generator. Water is cycled through the boiler directly from a system of filters in San Francisco Bay, with an intake beneath the surface that passes up to 10 cubic meters a second. After being used to help keep the steam turbine cool down, the water is returned to the bay 50 degrees Fahrenheit hotter than before. Along with the burned fuel released into the atmosphere from the peaking generators, the heated water has led to social concerns regarding pollution and the continued environmental viability of the plant’s processes.

Atlanta-based Mirant acquired the plant from PG&E in the early 2000s. However, in 2010, the Trans Bay Cable was put into commercial use. The Cable is a powerful electric line that provides San Francisco with enough coverage to fully replace the output from the Potrero station. Due to a lack of need and mounting public discontent with older technology, the mayor of San Francisco, Gavin Newsom, announced on December 21, 2010 that the Potrero Generating Station would be shuttered by the year’s end.  Its closure has been seen as a victory for environmental advocates.