The San Francisco Bay could soon become more than just a beautiful backdrop to Fog Town: It could become the engine that powers the city itself. This week, San Francisco became the first major U.S. city to investigate commercial tidal power, when it signed on to a $2 million pilot project to generate electricity using the tides in the bay. Every day, almost 400 billion gallons of water rush through the mouth of the San Francisco Bay — more than enough to power the entire city, if the energy from the tidal movement could be captured. The pilot project, however, will generate just one megawatt of electricity, produced when water flowing through underwater concrete passageways creates suction, thereby pulling air from pipes connected to onshore turbines and causing them to turn. The lack of moving underwater parts means the project would be easy to maintain and, hopefully, have limited impact on marine life.