Tidal Energy Devices convert the kinetic energy from the currents flowing in and out of tidal areas using this energy to generate electricity. The strength of the marine currents generated by the tide varies, depending on the position of a site on the Earth, the shape of the coastline and the bathymetry. Along straight coastlines and in the middle of deep oceans, the tidal range and marine currents are typically low. Generally, the strength of the currents is directly related to the tidal height of the location.
Tidal stream resources are therefore generally largest in areas where the water depth is relatively shallow, where a tidal range exists, and where the speed of the currents is amplified by the funnelling effect of the local coastline and seabed; for example, in narrow straits and inlets, around headlands, and in channels between islands. Entrances to lochs, bays and large harbours often have high current flows. In particular, large marine current flows exist where there is a significant phase difference between the tides that flow on either side of large islands. A good in-stream tidal site is one that has bathymetry and seabed properties that will allow a tidal stream device to be sited, has minimum or no conflicts with other uses of the sea space, and is close to a load and grid interconnection.
Orkney is recognised internationally as having one of the best resources in Europe for testing and developing wave and tidal technologies. The interaction of two independent tidal systems in the North Sea and the North Atlantic results in the complex and often powerful tides around Orkney’s coastline. The tidal waves of both systems have anti-clockwise rotations and they both reach Orkney’s coastline moving in opposite directions, but with similar strengths. These tidal streams can be influenced by surge conditions and powerful winds which are common in Orkney.