Mirant

Mirant's Potrero power plant

Updated Nov. 22, 2010 at 5:45 p.m.

A $505 million underwater electrical cable linking power plants in Pittsburg in the East Bay with customers on the San Francisco Peninsula is poised to begin commercial operations, potentially leading to the closure of an aging electrical facility.

The recently built Trans Bay Cable is already operating, but on Tuesday it will become a formal part of California’s electrical grid, which is managed by the quasi-governmental California Independent Systems Operator (the ISO).

Reliable ongoing operation of the Trans Bay Cable could lead to the closure of Mirant Corp.’s natural gas burning Potrero Generating Plant, which is the only major power plant still burning fossil fuels in San Francisco.

The 400-megawatt cable will be capable of importing more electricity from the East Bay into San Francisco than the Potrero plant produces under normal circumstances.

Neighbors and city leaders have tried for years to shut down the Potrero neighborhood plant, which is located on Illinois Street between 22nd and 23rd streets. They complain that it damages Bay water, creates air pollution and occupies valuable waterfront real estate between planned redevelopment projects. 

But efforts to shutter the plant have been stymied by its designation as “reliability must run” by the ISO, meaning it is needed to prevent blackouts.

Once the ISO removes the power plant’s must-run designation, it will be shut down under a settlement agreement secured last year by City Attorney Dennis Herrera.

The ISO plans to remove the power plant’s must-run designation after the Trans Bay Cable is operating reliably and after Pacific Gas & Electric has completed some in-city rewiring projects, spokeswoman Stephanie McCorkle said Monday.

“We’re not putting a time element on the length of commercial [Trans Bay Cable] operations — only that its commercial operation will have to meet our expectations,” the ISO's McCorkle said.

PG&E expects to complete its rewiring projects by the end of this year, spokesman Joe Molica said.

Construction of the Trans Bay Cable was completed earlier this year, but vibration problems prevented it from operating commercially.

The vibration problems were based at a substation, where the cable connects with San Francisco’s grid, according to P.J. Johnston, spokesman for the consortium that built, owns and operates the massive piece of infrastructure.

Supervisor Sophie Maxwell, whose district includes the Potrero plant, lauded its potential closure.

“This is great news for us,” Maxwell said. “It’s one of the oldest plants in California, and it’s spewing out large amounts of pollution. Everybody deserves to be breathing the best air they can."

Maxwell said she expects the ISO to remove the plant’s must-run designation after two months of successful commercial operations.

The city originally planned to build a natural gas-fueled power plant in the Bayview district to help force the closure of Mirant’s facility.

But that controversial plan, which was championed by then-Board of Supervisors president Aaron Peskin and other public power advocates, was nixed after Mayor Gavin Newsom expressed concerns about its health and environmental impacts.

In a statement, Mayor Gavin Newsom described the Trans Bay Cable's pending commercial operation as an "important step" that will allow the closure of the Potrero plant and "improve the air quality and public health for our city’s southeast and Potrero Hill communities.”

East Bay power plants and renewable energy projects, including some that are imagined under San Francisco's planned CleanPowerSF program, will produce additional electricty to help serve hundreds of thousands of residential and business customers that currently rely on the Potrero Power Plant.