Trans Bay Cable Pumps Pittsburg Power into San Francisco

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In 1998, a construction crew error disrupted a Pacific Gas and Electric Company substation in San Mateo, cutting power to 250,000 San Francisco customers for up to six hours. Traffic jams materialized as signals went dark. Streetcars and electric buses shut down. Water pressure dropped, as pumping stations ran on emergency power. The San Francisco Fire Department answered calls from at least 50 high rise buildings about people trapped in elevators.

The event, along with a series of brownouts that occurred a few years later – some of which were triggered by electricity market manipulation in the early-2000s – suggested a weakness in the grid.  With two aging power plants – at Hunters Point and Potrero – in San Francisco, increasing reliance on transmission lines coming from just one direction – the Peninsula – and the ever constant threat of earthquakes, energy regulators searched for ways to improve reliability.

Amidst calls to shutter the Hunters Point and Potrero power plants, led by Dogpatch-based San Francisco Community Power, among others, the California Independent System Operator – responsible for grid reliability – identified a 53-mile power line submerged under the Bay from Pittsburg to the Central Waterfront as the solution.  The project was pushed by Trans Bay Cable, a private firm. The cable was slated to deliver 400 megawatts (MW), approximately 40 percent of the City’s peak power requirements, produced from generating stations located in Contra Costa County.

The Trans Bay Cable was completed in 2010.  The Potrero Power Plant, which had become the most polluting generator in the state, closed in 2011, several years after the Hunters Point facility had been decommissioned.

“TBC provided San Francisco with an added level of power security, and it contributed to the City’s ability to shut down the Potrero Power Plant, and it diversified the power transmission options in San Francisco,” said PJ Johnston, spokesperson for Trans Bay Cable.  He added that given environmental concerns, and that the plant was well into its fifth decade, it likely would have been closed regardless. “Potrero would have had to be replaced if it were not for TBC; and the cost of replacing Potrero would have dramatically exceeded the cost of TBC,” he asserted

The then owner of the Potrero Power Plant, Mirant, had tried to vastly expand the facility, but was rebuffed by community advocates, including the Potrero Power Plant Citizens Task Force and SF Power, some of whom similarly opposed development of the Trans Bay Cable. The cable’s cost – eventually $505 million – seemed excessive for those who believed building a network of smaller resources, including solar, wind, and better energy management, would ultimately be more reliable and less expensive.

Submerging electrical cables has become big business in the last decade, with sales of high voltage submarine cable reaching $1.9 billion in 2014; a figure that’s expected to triple in the next 10 years. While sinking cables underwater is nothing new – telegraph cables first crossed the Atlantic Ocean in the 19th Century – the trend with electrical cables is.  For Siemens, which has been in the cable business since there was such a thing, the Trans Bay project allowed it to unveil a new technology, HVDC Plus, which has become one of the top two selling underwater transmission technologies on the market.

Laying wire underwater takes less time than burying it underground on land.  But the lines and associated technology can be expensive. Since alternating current (AC), utilized in the modern era, isn’t as efficient underwater or over long distances, power is converted to direct current (DC) for transmission. That means more costly cable and converters on each end. Trans Bay cable, about 10 inches in diameter, is buried four to six feet under the Bay bottom, or, where that wasn’t feasible, laid on the Bay floor covered with concrete “mattresses.” An AC to DC converter is located in Pittsburg; its DC to AC counterpart is at 23rd and Illinois streets.

Despite an initial delay due to the original AC converters being inadequate, the Trans Bay Cable has performed reliably, with only one incident since its opening.

On September 5, 2014, the M/V Ocean Life, a 225-meter cargo ship, lost power near the Benicia-Martinez Bridge and dropped a seven-ton anchor that came into contact with the cable. Although there was no immediate loss of service to the City, damage was sustained, causing Trans Bay to shut-down for more than four months to conduct repairs, a period in which the City experienced no outages. Trans Bay settled out of court earlier this year after suing the ship’s operators. According to Johnston, the cable has had a 99.9 percent availability rate since then.

The Trans Bay line is maintained and operated by Pittsburg Power, which is run by the City of Pittsburg. Trans Bay Cable pays Pittsburg for the service, recouping its cost plus a designated profit through what’s called a transmission revenue requirement, which it requests from the Federal Energy Regulatory Commission (FERC). Although Trans Bay has requested annual recoupments of upwards of $140 million, the actual amount to be paid was initially set at $132.5 million and has since dropped to $130 million. Trans Bay reported the percentage of power it’s supplying San Francisco as being closer to 50 percent than the 40 percent previously estimated, and as high as 57 percent in 2013. However, according to the California Independent System Operator, which regulates 80 percent of the state’s power flow, including the Trans Bay Cable, the line can convey no more than 400 MW to the City.  Demand for power over the period has fluctuated, but generally declined. 

Trans Bay’s ompensation is broken-up into high and low voltage costs. The low voltage allotment, $9.3 million, is spread among all PG&E customers. The high voltage share, $120.7 million, is dispersed among energy users who fall under the jurisdiction of CAISO.

“The key take away for a San Francisco customer is we pay a small fraction – about $1.3 million – of the overall revenue requirement, as it’s socialized over a much larger customer base,” Johnston explained. The more than half-billion dollar cost of establishing the cable is being recouped from all customers over 30 years, at roughly an extra 25 cents per consumer per year.

The project has contributed to the City’s coffers. The cables cross Port of San Francisco land; as part of the leasing agreement the City received $3.5 million upfront, and an additional $2 million a year for 10 years, adjusted for inflation. The Port itself is paid $550,000 annually over the same time period.

According to Steve Kech, public relations officer for the San Francisco Public Utilities Commission, “The money is intended for projects that will increase energy efficiency and renewables in City departments and installations, especially those which serve low-income, economically disadvantaged communities. Also, there is a green jobs training component.”

To date, SFPUC has invested $3.9 million to support renewable projects at Thurgood Marshall, Cesar Chavez and Downtown high schools, and HVAC retrofits for the Departments of Public Health, Human Services, and Recreation and Park. It also has spent $585,000 for the College Hill Learning Garden, a demonstration plot at 336 Elsie Street designed to teach students about ecologically friendly water, food, energy and waste systems.

According to Kech, the remaining $7.5 million collected thus far is earmarked for similar projects, in partnership with the San Francisco Unified School District. “They will feature solar, energy storage, and energy efficiency technologies,” he added.

The City also gained an additional $1 million in a settlement with Mirant, which was spent on a variety of health-related initiatives in District 10.

The environmental effects of submerging electrical cables are largely unknown. One reason the method has become attractive to power companies is because they don’t face the opposition engendered by attempting to erect power lines next to people’s homes. Before it was approved, Trans Bay competed against other transmission proposals that involved running an electrical line along the San Mateo Bridge, or a different undersea cable from Oakland; both required additional power lines on land before reaching the Bay. The power industry claims that high-voltage DC power doesn’t produce the same electromagnetic field as AC that so often concerns neighbors. 

The Trans Bay Cable runs parallel to the migratory route of the Chinook salmon, steelhead trout and green sturgeon. In 2014, a collaboration of the Electric Power Research Institute in Palo Alto, the Biotelemetry Laboratory at the University of California, Davis and the Universidad Miguel Hernandez de Elche in Spain, with assistance from Trans Bay, measured magnetic fields along the cable. The measurements will be used in future studies examining possible behavioral modifications in fish.

Megan T. Wyman, of UC Davis, declined to comment to the View, but said the group would be completing their analysis in the next few months. The Sierra Club and Natural Resources Defense Council also wouldn’t make an statements on the issue. In other places of the country, environmentalists have supported underwater cables as allowed municipalities to tap into renewable energy sources located elsewhere. The cost of urban land makes locating large wind farms in cities, for example, difficult.

One of Trans Bay’s promises was that it would connect the East Bay to San Francisco, enabling the City to tap into clean energy sources from the north. However, it’s unclear how much electricity flowing through the cable is from such resources. Pittsburg Power, with a major electrical substation that ties to the grid, obtains energy from several power generators throughout the West Coast. Until last month, when it was abruptly deleted shortly after a View inquiry to the company, on its website Trans Bay Cable reported that while renewable energy is included, “because of the diversity of its energy sources, it is impossible to identify the specific sources of power the Cable will receive.”  There are two large privately-owned natural gas-power generating facilities in Pittsburg.

The lack of transparency related to  where power comes from adds fuel to critics like the Environmental Defense Fund’s (EDF) James Fine.  Fine, working alongside SF Power, saw the issue six years ago as a fork-in-the-road, in which San Francisco chose to continue to rely on fossil fuel-based electricity rather than redirecting efforts toward dispersed, community-based, renewable energy sources. In the long run, Fine, an economist, believes that projects like Trans Bay will be more costly and less reliable than environmentally-friendly alternatives.

In a letter he co-wrote and circulated when the Trans Bay Cable was proposed, he stated, “In an era of steadily rising energy prices and global climate change, we can’t afford to keep using multiple transmission straws to suck-up huge amounts of power from traditional fossil fuel sources.” The letter was co-authored by Steven Moss, who is the View’s publisher and directed SF Power, and M.Cubed economist Richard McCann.

Meanwhile, as PG&E continues a clean-up of the old power plant at 1201 Illinois Street, Associate Capital recently purchased the 21-acre site from Mirant’s successor, Houston-based NRG Energy.  For his part, Fine wonders whether this is another missed opportunity for San Francisco. He suggested the parcel could have used the power infrastructure already in place from the old plant to tap into the grid in more creative clean energy ways, such as an energy garden featuring solar, a modestly-sized wind farm or tidal power.

Future energy options may indeed have to be more innovative.  If the former Potrero Power Plant site is used for housing, Fine suggested construction could center on making them zero-energy buildings, structures that put as much back into the grid as they consume. In addition to being equipped with solar rooftop gardens, he said that the development could incorporate a community cooperative offering self-driving electric vehicles.  Those shared cars, while unused, could put excess power back into the grid.