Decommissioning the Potrero Power Plant, the City’s largest single source of polluting air emissions, continues to be elusive.  Technical flaws discovered in the Trans Bay Cable may delay the plant’s expected closure at the end of this year.  Last month tests found a component of the 53-mile long cable wasn’t working properly.

The cable runs along the Bay floor from Pittsburg to San Francisco, and is expected to provide enough electricity to allow the Mirant-owned Potrero Power Plant to cease operations of Unit 3, the plant’s largest generating unit, which emits pollution 24 hours a day. The California Independent System Operator (Cal-ISO), the body that governs the state’s grid reliability, had recently agreed that three smaller units – 4, 5 and 6 – can be closed after several Pacific Gas and Electric Company (PG&E) intra-City transmission upgrades are completed this fall.

City leaders had all but promised that plant closure would come by year’s end. Now, they’re angry and frustrated.  “This is unacceptable,” said District 10 Supervisor Sophie Maxwell. “Here we are with no real idea of when this will happen. We want [the Potrero Power Plant] closed this year and we are going to have to figure it out some way.”

The Trans Bay Cable is 10 inches wide and includes two electric transmission and one fiber optic communication lines. It’s designed to transmit up to 400 megawatts of power, or 40 percent of the City’s electricity needs.  The project is estimated to cost $505 million.  Sean O’Reilly, the Trans Bay Cable project’s chief financial officer, told the Board of Supervisors Land Use and Economic Development Committee that the cable’s flawed component was installed by Siemens Power Transmission and Distribution Inc., and that Siemens will pay a daily penalty until the problem is fixed.  “It’s too early to tell when we are going to get the facility placed into commercial operations,” O’Reilly said. “But, we hope it will be this year.”

Following years of pressure from residents, community activists and City officials, Cal-ISO’s Chief Executive Officer Yakout Mansour sent a letter to Mayor Gavin Newsom in February detailing the organization’s decision to remove Potrero units 3 through 6 from Reliability Must Run status. The decision came after PG&E provided data demonstrating that the Trans Bay Cable could reliably replace energy production from those four units.  “Once the Trans Bay Cable comes up and we’re convinced it’s reliable, we can remove Potrero 3, 4, 5 and 6 from must run status,” said Gregg Fishman, Cal-ISO’s public information officer. “It remains up to the plant owner whether or not to keep it in operations, but it is assumed they will take it off line.”

Mirant has promised to do just that, and has been working with community leaders to determine the best use of the 27-acre power plant site in Dogpatch once the generating facility is closed.  Under a shut-down agreement brokered by City Attorney and Dogpatch resident Dennis Herrara, Mirant will receive a $2 million credit to offset planning and development costs charged by the City in exchange for closing the plant.