Over 70 per cent of the Earth is covered by water. The ocean is subject to the impact of wind, tides and ocean currents and thus carries with it large quantities of energy.
This means that the 'fuel' is inexhaustible and free. The different forms of ocean energy also have relatively little impact on the environment.
New technologies with great potential
Researchers and engineers worldwide are working to develop technology that can transform the energy in the ocean into electrical energy. Although the new technologies have great potential, they are still under development. Their significance in future energy systems is hard to predict.
The new hydro power variant that has the greatest potential is sea wave power. Waves generated by wind and currents could contribute significantly to a carbon neutral energy system. So far, wave power is in the developmental stage and harnessing wave energy still presents technical challenges.
Rapid progress in wave power
Wave power plants must be capable of producing a reasonable amount of power in light winds and small waves just as in stormy weather and rough seas. They must also be able to handle the physical strain the ocean exposes them to, and must have a minimal impact on animal and plant life. But progress is rapid and major research projects are underway in several countries.
Tidal energy uses the difference in water level between high and low tides as well as the currents created by tides in bays or along coasts. Tidal currents are extremely predictable, a major advantage in terms of planning generation and maintenance.
Tidal power plants have been used on a small scale in places like France since the 1960s, though the potential of tidal power as a large-scale energy source is not entirely certain. The main limitation is that very few locations are suitable for major tidal power plants.
Osmotic power, sometimes called salinity power, is a method of harnessing the energy released when fresh water is mixed with salt water.
In an osmotic power plant, fresh and salt water are directed into separate storage containers. The containers are separated by a semi-permeable membrane which lets through water molecules but not the larger salt molecules. The salt molecules in the salt water draw the fresh water through the membrane, creating osmotic pressure in the salt water container. The pressure is then used to power a turbine which generates electricity.
Great potential – but technology still expensive
Osmotic power is a renewable energy source and could in theory be used everywhere fresh water flows into salt water. The potential is great, but the technology is still expensive. The greatest challenge lies in improving the membranes and making them less expensive. The world's first osmotic power plant, opened in 2009, is located outside Oslo, Norway.