Tidal Power

Tidal Power - renewable power for cities

What is tidal power?

Tidal power is used in some of the oldest ocean energy technologies. Tides are caused by the gravitational pull of the moon and sun, and the rotation of the earth. Coastal areas always have two high tides and two low tides every 24 hours. In order to produce electricity, the difference between high tide and low tide (tidal range) must be at least 10 feet.  Tidal power is also known by related terms, tidal energy, wave power and wave energy that are used interchangeably and with slightly different applications and technologies.

Are there tidal power generators in the United States?

There are only about 40 places on the Earth where tidal ranges are great enough to produce electricity. At this point there are no tidal power plants in the U.S., but some promising early tests are being undertaken. The northeast coast of the U.S. and the Pacific Northwest has the potential for tidal power development.

How is tidal power harnessed?

Barrages or dams change tidal energy into electricity by pushing water through turbines, powering a generator.

Tidal fences look like giant turnstiles. They can span across channels or between small islands. The turnstiles rotate via tidal currents. These currents run up to 9 miles per hour and produce as much energy as winds of much higher velocity. Since water is much denser than air, ocean currents have much more energy than air currents.

Tidal turbines look like wind turbines. They are laid out underwater in rows, like a wind farm. The turbines are most effective when coastal currents are between 4 and 5 mph. In that situation a 50-feet diameter turbine could generate as much energy as a wind turbine with a 200-feet diameter. Tidal turbine farms are best constructed close to shore in water 70 - 100 feet deep.  An ideal location for tidal turbines is in the channel under the Golden Gate Bridge in San Francisco.  There are studies underway to determine the environmental impact of tidal power turbines in that channel. 

What are the environmental impacts of tidal power plants?

Barrages, and tidal fences disrupt marine life by blocking migratory paths. Silt builds up behind such facilities and can disrupt ecosystems. Tidal turbine farms may be easiest on the underwater landscape, as they don’t block migratory paths.

Are tidal power plants economically feasible at this point?

Construction costs of tidal power plants are very high, so payback periods are long. Once a plant is built, operating costs are low. At this point electricity generation via tidal power plant is not competitive with conventional fossil fuel power plants, but will improve with the success of a few initial projects and refinement of the technology.

Tags:  Tidal power, harnessing tidal power, wave tidal power, tidal power generator, tidal power renewable energy, tidal power model

Source:  US Department of Energy - Tidal Power