Friday, January 12, 2007

Tidal Energy

There is an abundant source of renewable energy beneath the Golden Gate Bridge that could theoretically generate enough electricity to power the whole city of San Francisco. Last year there was much discussion about the possiblity of harnessing the power of the tides that flow in and out of the bay in order to provide power to the City. One company estimates that those waters could generate 1,000 MW, which would be more than enough to satisfy San Francisco's power needs.

How exactly is tidal energy possible? Tidal power is achieved by capturing the energy contained in moving water mass. Two types of tidal energy can be extracted: kinetic energy of currents between ebbing and surging tides and potential energy from the difference in heigh between high and low tides. One method of extracting this energy is by constructing a barrage and creating a tidal lagoon. The barrage traps a water level inside the basin. Head is created when the water level outside of the basin or lagoon changes relative to the water level inside. The head is used to drive turbines. In any design this leads to a decrease of tidal range inside the basin or lagoon, implying a reduced transfer of water between the basin and the sea. This reduced transfer of water accounts for the energy produced by the scheme. The largest such installation has been working on the Rance river (France) since 1967 with an installed (peak) power of 240 MW, and an annual production of 600 million kWh (about 68 MW average power).

Tidal power has an efficiency rating of about 80%, which compares favorably to other renewable energy sources like solar power. However, this is one drawback to using tidal power; it doesn't produce energy 24 hours a day. As the tidal cycle is based on the period of rotation of the Moon (24.8 hours) and the demand for electricity is based on the period of rotation of the earth (24 hours), the energy production cycle will not always be in phase with the demand cycle. Another potential problem is that bulidng power turbines or dams beneath the water sometimes causes damage to the marine habitat.

Despite these drawbacks, I feel that tidal power is an exciting possibility that should be further explored. The San Francisco Bay is considered by many energy specialists to be one of the best sources of tidal energy in the world. The main problem that faces a project like this is one that usually hampers any effort to pursue alternative energy... a lack of funds. The city government of San Francisco is hesitant to provide funding to a project like this due to concerns of cost overruns and construction management issues. Private companies, such as Hydroventuri, have expressed interest but have so far been unable to come up with the necessary money.

It is unfortunate that private and public leaders cannot work together to reach a solution for getting this project up and running. A little bit of government spending could go a long way in stimulating some progress here but the issue has been tossed off to the side. I think our leaders should take some chances and start considering ways to fund this project. We have excellent source of renewable energy right at our fingertips and it is time to start using it to provide a cleaner future for our society.

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