Various forms of ocean energy, such as tides, waves and currents, are used to produce electricity. Countries such as South Korea, France, Canada and the UK have made great headway, opening exciting possibilities for sustainable energy generation.

There are many ways to generate electricity from the ocean, here are some of them:

Wave Energy

Wave energy converters capture the energy contained in ocean waves and use it to generate electricity. There are three main categories; oscillating water columns that use trapped air pockets in a water column to drive a turbine; oscillating body converters that are floating or submerged devices using the wave motion (up/down, forwards/ backwards, side to side) to generate electricity; and overtopping converters that use reservoirs to create a head and subsequently drive turbines.

Tidal Energy

There are three categories of tidal energy technologies. The first category, tidal range technologies use a barrage – a dam or other barrier – to harvest power from the height difference between high and low tide. The second category, tidal current or tidal stream technologies have had more than 40 new devices introduced between 2006 and 2013. The major differences among the devices are the turbines, which can be based on a vertical or horizontal axis, and in some cases are enclosed (ducted). The final category, hybrid applications are forms of tidal range technologies that have great potential if their design and deployment can be combined 4 Tidal Energy | Technology Brief with the planning and design of new infrastructure for coastal zones.

Salinity Gradient Energy

Salinity gradient power is the energy created from the difference in salt concentration between two fluids, commonly fresh and salt water, for example, when a river flows into the sea. There are two technologies for which demonstration projects are running and both use membranes. Pressure Retarded Osmosis uses a membrane to separate a concentrated salt solution (like sea water) from freshwater. The freshwater flows through a semipermeable membrane towards the sea water, which increases the pressure within the seawater chamber. A turbine is spun as the pressure is compensated and electricity is generated. Reversed Electro Dialysis (RED) uses the transport of (salt) ions through membranes. RED consists of a stack of alternating cathode and anode exchanging permselective membranes. The compartments between the membranes are alternately filled with sea water and freshwater. The salinity gradient difference is the driving force in transporting ions that results in an electric potential, which is then converted to electricity.

Ocean Thermal Energy Conversion

Ocean Thermal Energy Conversion technologies use the temperature difference between warm seawater at the surface of the ocean, and cold seawater at between 800–1,000 metres depth to produce electricity. The warm seawater is used to produce a vapour that acts as a working fluid to drive turbines. The cold water is used to condense the vapour and ensure the vapour pressure difference drives the turbine.