|Lunar Energy RTT Turbine. One of the different technology options available for tidal in-stream energy conversion (TISEC). Click to enlarge.|
Pacific Gas and Electric Company today signed an agreement with the City and County of San Francisco and the Golden Gate Energy Company to conduct the most comprehensive study yet undertaken to assess the possibilities for harnessing the tides in San Francisco Bay to create a new source of zero-emissions, renewable electric power for California energy customers.
The multifaceted study, the initial phases of which will begin this summer and are estimated to take approximately twelve months, will include thorough analyses of the Bay’s energy potential, the existing and emerging technologies to capture energy from tidal flows, the possible environmental impacts associated with such a project, as well as the economic feasibility and other costs and benefits of tapping this new energy supply.
If findings in the initial rounds of research affirm the feasibility and promise of tidal in-stream energy conversion (TISEC), future plans could ultimately lead to the development of a full-scale commercial project.
The study effort will bring together and draw on the combined resources and expertise of PG&E, CCSF and Golden Gate Energy. Specifically, PG&E is committing to provide up to $1.5 million to fund research by third-party experts, dovetailing with up to $346,000 contributed by CCSF for feasibility studies and stakeholder outreach. Golden Gate Energy, which currently holds key federal regulatory permits necessary to study the San Francisco Bay location, will work cooperatively to support the effort.
In addition to being clean and renewable, tidal power offers the advantage of being highly predictable and reliable. In addition, tidal power technology would be situated on the sea floor, avoiding the land-use and visual impact considerations associated with many other forms of power generation. In a 2006 study, the Electric Power Research Institute identified San Francisco Bay as one of the world’s most abundant potential resources for electricity generation using tidal power technology.
The EPRI report grouped TISEC water turbine technology into two types (like wind turbines):
Horizontal axis turbines in which the axis of rotation is horizontal with respect to the ground and parallel to the flow direction; and
Vertical or cross-flow axis turbines in which the axis of rotation is perpendicular to the flow direction.
Subsystems include rotor blades which convert the energy to rotational motion, a drive train and a supporting structure. Devices vary by:
Design of the support structure: gravity base bottom mounted, attached to a monopole foundation, or anchored and moored and allowed to float in the tidal stream;
Open vs. shrouded rotors;
Fixed versus variable pitchblades;
Yaw control versus fixed yaw angle; and
Drag vs. lift water foil (vertical axis only).