Unlike wind and sun, tides are always moving. Harnessing tidal energy is one of the greatest potential sources for renewable energy. They’re reliable, we can calculate the tides years into the future and they contain a huge amount of energy.
Harnessing tidal energy is not new. In France, tidal mills have existed since the 12th Century, used for grinding grain. These mills were built in shallow creeks by the coast. Gates were constructed that swung open inwards. As the tide came in, the waves pushed the gates open. When the tide turned, the gates were forced shut, forcing the retreating water to flow seaward through the watercourse of the mill.
The tides are 'powered' by the moon. The gravitational pull of the moon pulls the water in Earth’s oceans, creating a bulge on the side facing the moon. A second bulge on the opposite side of the Earth is created due to the centrifugal force of the planet rotating. These two bulges create our high tides. Tidal power captures the energy from the rising and lowering sea levels. There are two main types:
Tidal Flow Turbines
Tidal flow turbines are located in areas of strong currents and tidal flows, such as around a headland or close to estuaries or islands. They typically resemble wind turbines on the seabed, with propellers shaped to minimise the impact on sea life and to ensure the turbines do not get caught up with debris and underwater plant matter.
A number of manufacturers are now producing tidal flow turbines and they are being trialled in a number of places around the world. ScottishPower Renewables is currently installing a tidal array off the coast of Islay in Scotland. Consisting of ten 1MW Andritz Hydro Hammerfest HS1000 Tidal Turbines, the system will be fully submerged on the seabed and is expected to generate about 30GWh of electricity annually: sufficient to power the local communities living on the islands of Jura and Islay where the array is to be situated.