There are already several tidal generation works around the world humming, or splashing, along and providing almost free electricity. Since most of our population lives near the coast, shouldn't we considering developing moon, I mean tidal, power.
Comparing tidal energy to wind or solar energy reveals some major advantages:
· Tidal energy is reliable, predictable and does not depend on the weather. It doesn't go off-line when it's cloudy or when the wind stops blowing.
· Once the generation facility is built, tidal power is free.
· Maintenance is not expensive.
· No greenhouse gases or other waste is produced.
· Because seawater has a much higher density than air, ocean currents carry significantly more energy than wind.
· Newer turbine technology is said to cost about the same as wind power.
· This is a resource that's available worldwide from deep ocean waters.
· Construction of large-scale offshore devices results in new areas of sheltered water, attractive for fish, sea birds, seals and seaweed. And it presents no difficulty to migrating fish (except barrages and perhaps tidal fences). No birds are killed.
· Some turbines can be completely submerged and so are invisible to those who say wind farms ruin the view.
There are three main types of tidal power plants.
The Rance estuary station is a 240mw barrage type plant, the simplest tidal generating system Also known as an ebb generating system it involves a dam, known as a barrage, across an estuary. Sluice gates on the barrage allow the tidal basin to fill on the incoming high tides and to exit through the turbine system on the outgoing, or ebb, tide.
These plants are obviously very expensive to build and environmentally harmful. The environment is changed for many miles upstream and downstream. Many birds rely on the tide uncovering the mud flats so that they can feed. On the other hand, in some cases barrages can protect a large stretch of coastline from damage from high storm tides and they can be used as road bridges. There are relatively few suitable sites for tidal barrages. Currently France, China, and Russia operate barrage plants.
Tidal lagoon plants are similar to barrages, but use a man-made pool to store water. They eliminate many of the environmental damage caused by `traditional' barrages' and open more locations to this technology.
Tidal fences are a series of vertical axis turbines which are mounted within the fence structure, or caisson. Imagine giant turnstiles blocking a channel and forcing all of the water through the turbines. Tidal fences can also be used in unconfined basins, such as in the channel between the mainland and a nearby off shore island, or between two islands.
Tidal fences have less impact on the environment than barrages and are less expensive. A 2.2GWp tidal fence is being planned for the San Bernadino Strait in the Philippines. The project, estimated to cost $US 2.8 Billion and take 6 years to complete. Canadian company Blue Energy is a leader in this technology and has an informative site.
Offshore turbines promise simpler and less expensive tidal energy. These may resemble an underwater wind farm.
This is still very new technology, But an experimental tidal power station was installed in Kvalsundet, south of Hammerfest, Norway, and became operational in November 2003. The installed tidal power turbine generates a maximum of 300 kW at a maximum speed of the current of 2.5 m/s. Here's a link.
Another tidal turbine was installed two years ago off the Devon coast. If it performs as expected, the consortium behind it hopes to build a whole set of turbines in the area - a tidal farm. This is from a press release from the manufacturer:
[This photo shows the turbine raised for maintenance]
One of the more interesting recent developments in offshore turbines are anchored units that `float' in the tidal stream. Below is an illustration from SMD Hydrovision:
Tidal Energy Potential
It has been reported that tidal energy could supply 27% of Britain's power requirements. The EU JOULE II Energy Research Program in 1996 identified 106 locations of interest around the European coastline. The primary sites of interest are in the UK, France, Greece and Italy. The EU's Atlas program site has information on some potential and promising sites around the world. The World Energy Council also has a comprehensive list of sites on their tidal energy page.
I'm not aware of any large-scale studies done in the US to assess total potential. But the Maine coast has tremendous potential and near perfect geography for tidal energy development. Promising areas along the California and Northwest coasts have also been identified.
The US is lagging in tidal technology. Most design work seems to be done by British firms with the strong support of their government. When it comes to tidal Energy, Britannia may once again rule the seas.
Cross posted on European Tribune.