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 TIDAL STREAMSTidal streams are cyclical flows set up by the gravitational attraction of bodies in our solar system, particularly the moon and the sun. They vary in amplitude and direction roughly on a daily cycle and a monthly cycle but are very predictable and reliable in their occurrence. Recent studies have considered the UK’s tidal stream resource and produced the following predictions.
The last report by Black & Veatch (B&V) was prepared for the Carbon Trust under the Marine Energy Challenge programme. This report built on research carried out by Robert Gordon University (RGU) into the energy that can be extracted from a site without destroying the flow. Obviously attempting 100% energy extraction would result in a blockage to flow and zero energy extraction as the tidal stream would just look for a different and easier path. The B&V report considers a “flux” approach where the technically extractable energy in any channel is considered to be 20% of the energy flux flowing through that channel. The B&V report therefore gives lower levels of extractable energy than the other studies (see Table above). The extractable energy values quoted represents electrical energy after allowance for the overall conversion efficiency. The B&V report categorises the technically extractable tidal stream energy in the UK according to water depth and velocity range. More than 50% of the technically extractable energy is in water depths greater than 40 metres. Also over 90% of the economically attractive faster flowing sites (>3.5m/s) are in water depth of over 40m. Evopod is specifically targeted at regions with water depths greater than 40 metres and which are also exposed to harsh wave climates. Smaller Evopods can be installed in shallower water depths. |
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