Today, more than 25 countries are involved in developing relevant conversion technologies for harnessing ocean renewable resources for electricity generation and/or other purposes, such as desalination, heating for aquaculture and other uses.
Over 300 wave and tidal devices have been suggested up to the present time, but very few of these are in an advanced state of development. One technology, Pelamis, is leading in terms of development with a medium sized grid-connected scheme being installed in Portuguese waters now.
Ocean energy is mostly in an experimental stage and apart from the 40 year old tidal barrage at La Rance in France, the first ocean energy projects are now being installed and about to be commercialised.
The market is poised for expansion and is expected to grow to 1 GW of installed capacity at an annual market size of $500 million by 2015, but these figures are very broad. Investment to date in the ocean power market has been just over $500 million since 2001, which is relatively small compared to other renewable energy market segments. More than $2 billion will be invested to build commercial ocean wave power farms by 2015. Another $2 billion will go towards research and development globally over the next six years.
Energy can be harvested from the oceans in five basic ways, with a multitude of variations.
- Tides – Potential energy contained in tides can be harnessed by building barrage or other forms of construction across an estuary.
- Waves – Kinetic and potential energy in ocean waves can be harnessed using modular technologies.
- Tidal or marine currents – Kinetic energy in tidal (marine) currents can be harnessed using modular systems.
- Temperature gradients – Thermal energy due to the temperature gradient between the sea surface and deepwater can be harnessed using different Ocean Thermal Energy Conversion (OTEC ) processes.
- Salinity gradients – At the mouth of rivers where fresh water mixes with salt water, energy associated with the salinity gradient can be harnessed using pressure-retarded reverse osmosis process and associated conversion technologies.
Wave energy is the largest resource, followed by power from the salinity and thermal gradients. Tidal and marine current energy are by far the smallest in potential capacity.