January seems to be a sign of a much cleaner future for residents of San Francisco’s Southeast.

This month, Mayor Gavin Newsom received a letter from the CaliforniaIndependent System Operator (CAISO or Cal-ISO) that it anticipates allowingMirant’s power plant at Potrero to close at the end of the year. The closing ofthe power plant would mark the end of fossil-fuel plants in San Francisco; the other at Hunters Pointhaving closed in 2006. Closing the two plants have been environmental justicegoals of the City since the 1990s. Pollution from the plants has contributed torecord-high rates of asthma, cervical cancer and countless other ailments confrontinga historically African American portion of the City.

The CAISO was created by federal regulatory authorities to plan and manage California’shigh-voltage transmission grid, minimize black outs and keep utilities andmerchant generators from exploiting the markets used for sale of energy. TheISO prevents generators and transmission line owners from manipulating marketprices while ensuring electrical reliability in local areas.

For privately-owned facilities such as those at Potrero, CAISO determineswhether power generation is necessary for local reliability and whether it isappropriate to implement Reliability Must-Run (RMR) contracts that legally bindthe power plant owners. CAISO conducts studies annually about how contingencies in theelectrical grid could affect stable delivery of electricity and designatesmust-run status for generating units accordingly. Mirant has even expressedthat it would close the plant at Potrero once the ISO removes itsmust-run status.

Conceptually, I’ve found transmission to be an illusive component of electricpower. As electricity goes from power plant to power outlet, transmission is acritical infrastructure in between. Generators feed power into the transmissiongrid across long distances—sometimes across entire states—until the power isdelivered into a community’s distribution system, the series of power lineslining its streets.

Located at the top of the Peninsula, San Francisco is resource-constrained in that there issimply not enough transmission capacity to reliably import its entireelectrical load. This explains why, after over 10 years of staunch oppositionto the power plants, only one has successfully shut down.

The City’s strategy to close both power plants and get a cleanerelectrical portfolio relies on both renewable energy and reduced electricaldemand, in addition to more transmission capacity. However, the level ofrenewable energy and reduction in demand alone has not matched the generatingcapacity provided by the plants.

This is in part because of the difficulty in integrating many renewable resources.Solar and wind, for example, are intermittent resources whose hours ofoperation are controlled by environmental factors. The ISO cannot turn on theresources at-will as it can with fossil-fuel plants, or even hydroelectric orgeothermal plants. Technological innovation and adoption will hopefully addressthis weakness of renewable energy in the near-future.

In the end, it appears that increased transmission capacity will be largelycredited with eliminating the power plants in San Francisco. New transmission lines andupgrades are what primarily led to the 2006 closing of Hunters Point and arealso cited in this month’s letter to Mayor Newsom about Mirant’s plant. Inparticular, a public-private partnership produced a new underwatertransmission cable that connects San Franciscoto the East Bay.

The San Francisco Power and Utilities Commission (where I am spending myFellowship) has played an important role in implementing these equity-drivenenergy priorities of the City, and it is this leadership that hopefully willsee the release of Potrero’s must-run designation at the end of this year andthe close of the plant in the following year.

Copenhagen maynot have achieved what many would have liked, and even our own Congress appearsto have lost the urgency of confronting energy reform. However, as this examplein San Francisco shows, local governments are stepping up to the plate,thinking globally about the effect of climate change, and acting locally tohelp their own residents who have suffered from poor environmental stewardshipfor far too long.