What is Tidal Energy?
Harnessing the Power of Water
Traditionally the power of water has been harnessed through hydroelectric dams to produce energy. Now, researchers and developers in North America and Europe are working to deploy underwater turbines and wave energy converters to generate clean renewable energy.
Harnessing the power of water can be traced back to the 8th century CE, where the first tide mill was found in Northern Ireland. During high tide, sea water would fill a collection pond through a one-way gate. During low tide the gate would close automatically, and once the tide reached a certain level the stored water would be released to turn a water wheel which was used to crush grain. These early tidal energy converters function similarly to tidal barrages which are still being used to generate electricity to this day.
Today, as in years gone by, the natural rise and fall of coastal waters is still used to transform the energy created by tides into electricity or other forms of power. Sea currents are magnified by the gravitational fields of the earth, moon, and sun pulling the water over geographic features, such as headlands, inlets, and straits. The Bay of Fundy (home to the highest tides in the world), provides an excellent example of the abundant resource that can be used to generate power. In this 270 km ocean bay between the Canadian provinces of Nova Scotia and New Brunswick, the rise and fall of the tide can be as high as 16 meters. In twelve hours, 160 billion tonnes of seawater flows in and out of the Bay of Fundy during one tidal cycle, more than four times the flow of all the world’s freshwater rivers over the same time period. The movement of the tides is a significant renewable and predictable source of power.
Three ways to generate tidal energy;
Tidal Streams: A turbine, similar to a wind turbine, is submerged directly in an area of significant tidal change, such as the Bay of Fundy or Pentland Firth in Scotland. Tidal stream generators draw energy from the currents in the same way wind turbines draw energy from air currents. The major benefit of tidal stream generators is that water is 800 times the density of air, meaning more energy can be extracted by a smaller turbine.
Tidal Barrages: A dam-like structure is constructed across a bay or river that has significant tidal flow, such as the Annapolis Tidal station in Nova Scotia and the Rance Tidal Power Station in Brittany, France. Turbines are installed within the barrage wall, as the tide rises, gates in the barrage open allowing water to flow though. As the tide lowers these gates close, creating a pool or tidal lagoon – the water is then released through the turbines, generating energy.
Tidal Lagoons: A self-contained structure, similar to a tidal barrage, which partly encloses a body of ocean water by the use of a natural or man-made barrier or breakwater. An example of this is the Swansea Bay project in Wales. As the sea level rises against the breakwater a difference in water level is created, once the desired water level is reached sluice gates are opened and water flows freely into a lagoon and through turbines to generate electricity. This process then occurs in the reserve, on the ebb tide in the same fashion.
Currently, tidal stream generators, often referred to as tidal energy converters or tidal turbines, are the most economical and least ecologically damaging option among the three main forms of tidal power generation. The biggest challenge facing the tidal energy industry is building economical, effective devices that can withstand the extreme ocean conditions they are deployed in.
In areas like the Bay of Fundy, Nova Scotia and Pentland Firth, Northern Scotland, tidal energy companies are contending with some of the strongest currents in the world. The tides in the Bay of Fundy are semidiurnal (two highs and two lows each day), making it one of the best sites to install tidal turbines, the currents, however, make it extremely difficult to design, anchor/moor and maintain turbines in the bay.
Dynamic Systems Analysis (DSA) works extensively with companies in North America and Europe on the design, development and installation analysis of tidal energy converters. Common installation challenges such as assessing moorings, anchor requirements, power umbilical bend radius, and installation methods in sites like the Bay of Fundy are frequently addressed by DSA and users of the numerical modelling platform ProteusDS.