There are five different technologies under development, which aim to extract energy from the oceans.
- Tidal power: the potential energy associated with tides can be harnessed by building a barrage or other forms of construction across an estuary.
- Tidal (marine) currents: the kinetic energy associated with tidal (marine) currents can be harnessed using modular systems.
- Wave power: the kinetic and potential energy associated with ocean waves can be harnessed by a range of technologies under development.
- Temperature gradients: the temperature gradient between the sea surface and deep water can be harnessed using different ocean thermal energy conversion (OTEC) processes.
- Salinity gradients: at the mouth of rivers, where freshwater mixes with saltwater, energy associated with the salinity gradient can be harnessed using the pressure‐retarded reverse osmosis process and associated conversion technologies.
None of these technologies is widely deployed as yet, but significant potential exists. The IEA believes that these technologies could start to play a sizable role in electricity mix around 2030.