Tidal power generates electricity by capturing the energy contained in moving water caused by tides.
Capturing and Using Tidal Power
Tidal energy can be captured in two ways:
- Tidal Barrage
Tidal power can be harnessed using a barrage (dam) built across an estuary that captures the potential energy generated by the change in height (or head) between high and low tides. As the tide goes in and out, the water flows through tunnels in the dam. The ebb and flow are used to either turn a water turbine or compress air through a pipe that then turns a turbine, which generates electricity. -
Tidal Fences and Turbines
Tidal fences and turbines can also be used to capture tidal power. Tidal fences are turbines that operate like giant turnstiles, while tidal turbines are similar to wind turbines. In both cases, electricity is generated when the turbines are turned by the tidal currents that occur in coastal waters. Ocean currents generate relatively more energy than wind (air currents) because ocean water has a higher density than air and therefore applies greater force on the turbines.
Benefits
- Tides are completely predictable and therefore produce reliable power.
- Tidal current turbines should have low environmental impacts.
Challenges
- Compared to river dams, tidal barrages are very expensive and can affect a wide area upstream and downstream. Tidal barrages reduce the time mud flats are exposed and covered and therefore affect bird and other wildlife and fisheries.
- The relatively low head of water above the turbines restricts the capacity of individual generators to about 25—50 megawatts.
- All components and machinery must be able to withstand salt water and moving silt and sand.
Global Status and Potential
Only a few tidal energy sites are in operation around the world. Larger sites include the White Sea in Russia and the Rance River in France (the largest site in the world). Smaller tidal power plant have been built in Canada, such as the site at Annapolis Royal in Nova Scotia, and several in Norway. Together they have a total capacity of less than 250 MW.
However, the potential for tidal energy is immense; potential global tidal power exceeds 450 terawatts, most of it in Asia and North America.
Canadian Status and Potential
The Bay of Fundy between New Brunswick and Nova Scotia is the most promising location in Canada for tidal energy and could potentially produce as much as 30,000 MW of energy. Some Canadian companies are now developing tidal current generators.
