Tidal power plants
Tidal power plants use the difference in height between high and low tide. A dike or dam is built in front of a bay, in which several turbines are located that generate electricity. At high tide the turbines are driven by the incoming water, at low tide by the outgoing water. The world’s first tidal power plant was built in 1966 in France (Brittany), where the Rance River flows into the Atlantic Ocean in the Bay of St. Malo. The prerequisite for a tidal power plant is a tidal range of at least five metres.
Ocean current power plants
Ocean current power plants function similarly to tidal power plants, but use ocean currents rather than the energy of high and low tides. In simple terms, they work similarly to an upturned windmill, which is set in motion by flowing water instead of air. There are more than 100 known sites in Europe that would be suitable for generating energy from ocean currents, mainly along the Atlantic coast. Since the lunar calendar can be used to calculate how fast the current is on any given day, hydroelectric power plants provide predictable electricity – one of the main disadvantages of wind and solar energy. The world’s largest hydroelectric power station went into operation off the coast of Northern Ireland in 2008 and supplies 1.2 megawatts of energy.
Wave power plants
Wave power plants convert the kinetic energy of ocean waves into electricity. Various technological processes are used for this. In Scotland, the “Oyster” wave power plant – because it looks like a shell – was commissioned in 2009. Spain followed in 2011 with the “Mutriku” wave power plant.
In addition to this “mussel shell principle”, there are a number of methods for using waves as an energy source. The pelamis, a “sea snake”, is a steel tube more than 100 meters long, composed of several elements, which are positioned in the direction of the waves on the sea. Hydraulic cylinders sit in the hinges of the segments, which are moved up and down with the waves and drive power generators.
Other ways of harnessing the power of the sea include osmosis power plants, which use the different salt content of seawater and river water to generate energy. Possible locations for such plants are found where rivers flow into the sea. Ocean Energy Conversion Technology (OTEC) in turn generates electrical power from the temperature difference between cold and warm water masses at different depths of the oceans. These ocean thermal power plants are usually built as floating plants at sea. Although this method of generating electricity has great potential, there are currently only a handful of test power plants.
What becomes obvious is that electricity generation from the sea is only in its initial phase and no technology has yet made a breakthrough. Some plants are already producing electricity, but the involved costs of generating electricity are still too high. However, if this investment and research barrier can be overcome, marine energy can make an important contribution to a green future.