Harvesting energy from the sea
The bodies of water across our globe have been a relatively unexplored source of energy, compared to the high-profile wind- or solar-energy technologies. But in the future a large portion of our electricity could originate from the underwater currents or the waves that continuously hit our shores.
Strangford Lough in County Down, Northern Ireland, is the largest lough of the British Isles. In April the lough became home to SeaGen, a 1000 ton commercial tidal energy converter. The turbines, which are secured to the sea floor, operate like submerged windmills, but can be driven by high tidal current velocities or continuous ocean currents.
One principal reason for the choice of location at Strangford Lough is that it is one of the most aggressive tidal streams in the United Kingdom, offering an optimal energy flow. SeaGen can operate up to 20 hours per day, harnessing the energy of both ebb and flood tides. It will produce four times electricity than any other current tidal stream project. The energy converter has a generating capacity of 1.2 megawatts, providing approximately 800 homes with electricity.
Although the system is capable of generating commercial amounts of electricity from a sustainable source, there are still other environment issues to be considered. Strangford Lough is a conservation area and home to various wildlife. A particular concern is that the 16 metre rotors could be hazardous to curious seals or benthos (organisms living on or near the seabed). Common Seal, sometimes called Harbour Seal, populations have already been on the decline throughout Western Europe.
Another potential energy source is wave energy. The wave energy converter Pelamis is a series of semi-submerged cylindrical sections connected by hinged joints. The electrical generators are powered by the relative motion between the sections via a hydraulic system. Three Pelamis Converters will be deployed off the coast of Portugal as the world's first wave farm.
Another energy converter is the Wave Dragon, which has been under trial in Danish waters since 2003. The operational principles are similar to that of a traditional hydro-power plant. The waves are directed into an above-sea-level reservoir, from where the water is released back into the sea through hydro turbines. With the trial over, a commercial demonstrator is being developed for 2009. The first large Wave Dragon with a 7 megawatt capacity will be deployed in Wales.
Wave energy could be harvested along many coasts throughout the world (e.g. west coast of Europe, west coast of the United States, Chile, Australia and New Zealand). The large coastal populations could benefit from locally produced electricity, which could ultimately cover over half of the world's electrical demands.
The technology for wind energy has enjoyed a head-start over the last thousand years. Wave energy has only been a serious sector for research since about twenty years. It is hoped that wave energy will be able to rival wind energy in the next ten years.
After the successful operation of the commercial demonstrators it is expected that the cost of production will continuously fall as more developers and investors become involved. The growth of these technologies will lead to new possibilities for renewable energy sources.