Surf's up: Harnessing the power of the ocean

While the predictable nature of tides makes them an ideal renewable energy source - more so than wind - the ability to effectively harness energy from the tides has proved elusive. But times are changing.

New research in support of tidal energy technology has been published in a special issue journal of the Royal Society, by a global group of scientists and engineers from several institutions including the University of Southampton. The University is home to the Southampton Marine and Maritime Institute (SMMI), a world-leading centre of excellence in the areas of marine and maritime research.

AbuBakr Bahaj, professor of sustainable energy at the University of Southampton and editor of the special issue, says, ''The energy present in marine currents can be converted using technologies not too dissimilar to those used in wind energy. While technologies harnessing energy from the tides and currents have been discussed for many years, it is evident from recent deployment of single devices at megawatt scale that real progress has been achieved in a very short period of time.

''In essence, experience with single machines at such a power capacity, will make progress to deployment of multiple machines to convert the marine energy resource much faster than that achieved at the start of the wind energy industry.''

Although the potential for marine energy conversion clearly exists, the technology is presently still at the commercial prototype phase and only a handful of devices have so far been tested at full scale in the ocean. Unlike wind energy, there are a variety of designs under test, with no single device design emerging as a winner so far.

Tapping the tide
Engineers attempt to harness the tides in two ways. One involves building barrages across tidal estuaries to make use of tidal differences in sea surface elevation - forcing the flowing waters to turn turbines in a similar fashion to hydroelectric power installations.

The other method involves placing turbines underwater in areas of the sea where fast-flowing tidal streams are found, such as those in coastal waters around the Channel Islands and Scotland. This technology is broadly similar to the three bladed turbines used in wind energy.

Developing power from offshore tidal streams is fraught with difficulty, but according to the authors of the latest research, 2013 could see a big breakthrough in tidal stream power.

There are several companies planning to deploy arrays of tidal turbines in UK waters, including the MeyGen tidal stream project in Scotland's Pentland Firth. This will initially generate up to 40MW of electricity, enough to power 38,000 homes.

''This project is a crucial milestone for technology development and deployment. Currently, it appears this will be the first deployment of an array of tidal stream turbines,'' says Professor Bahaj. ''Such deployment will give a boost to the industry as it will also provide the needed data of operation in one of the most energetic areas of the sea. Overall, tidal power will also give us another component in the energy mix that's more energetic and reliable than wind.''

 In the UK, tidal power has the potential to meet more than 20 per cent of the country's electricity demand.