Wave and Tidal Energy

Tidal power
Harnessing the tides in a bay or estuary has been achieved in France (since 1966), Canada and Russia, and could be achieved in other areas with a large tidal range. The trapped water turns turbines as it is released through the tidal barrage in either direction. Another possible fault is that the system would generate electricity most efficiently in bursts every six hours (once every tide). This limits the applications of tidal energy.

Tidal stream power
A relatively new technology, tidal stream generators draw energy from currents in much the same way that wind generators do. The higher density of water means that a single generator can provide significant power. This technology is at the early stages of development and will require more research before it becomes a significant contributor.

Several prototypes have shown promise. In the UK in 2003, a 300 kW Periodflow marine current propeller type turbine was tested off the coast of Devon, and a 150 kW oscillating hydroplane device, the Stingray, was tested off the Scottish coast. Another British device, the Hydro Venturi, is to be tested in San Francisco Bay.

The Canadian company Blue Energy has plans for installing very large arrays tidal current devices mounted in what they call a 'tidal fence' in various locations around the world, based on a vertical axis turbine design.

Wave power
Harnessing power from ocean surface wave motion might yield much more energy than tides. The feasibility of this has been investigated, particularly in Scotland in the UK. Generators either coupled to floating devices or turned by air displaced by waves in a hollow concrete structure would produce electricity. Numerous technical problems have frustrated progress.

A prototype shore based wave power generator is being constructed at Port Kembla in Australia and is expected to generate up to 500 MWh annually. The Wave Energy Converter has been constructed (as of July 2005) and initial results have exceeded expectations of energy production during times of low wave energy. Wave energy is captured by an air driven generator and converted to electricity. For countries with large coastlines and rough sea conditions, the energy of waves offers the possibility of generating electricity in utility volumes. Excess power during rough seas could be used to produce hydrogen