The other type of renewable energy resources that come from ocean are wave energy, tidal energy, and ocean thermal energy conversion.
Wave energy is a type energy obtained directly from surface wave or surface wave under pressure. The waves are generated from winds blowing from the surface of sea or ocean. Wind itself is a function of temperature and pressure differences across the globe caused by distribution of solar energy.
Wave energy carries kinetic energy and gravitational potential energy. The energy is a function of height and period of waves. Wave Energy Converter (WEC) is used to convert wave energy into electricity.
Figure below shows global offshore annual wave power distribution.
It can be seen that the north and south zones are the best sites for capturing wave power. The prevailing winds in these zones blow strongest in winter.
The oceanic wave climate (far offshore) offers abundant energy levels. As waves approach the shore, energy is dissipated, leading to lower wave power levels on the shoreline. Therefore the energy availability is sensitive to location and the distance from the shoreline.
Table below shows regional theoretical potential of wave energy. The largest potential of wave energy is in Asia and Australasia.
Oceanic tides are the function of the motion of the moon and sun relative to the earth. Tidal stream is the vertical rise and fall of water is accompanied by an incoming (flood) or outgoing (ebb) horizontal flow of water in bays, harbors, estuaries and straits. To convert kinetic energy in water currents into electricity, tidal stream devices are used. The principle is similar to wind turbines.
Ocean Thermal Energy Conversion (OTEC)
15% of total solar energy is approximately retained as thermal energy and stored as heat in the upper layer of ocean. This energy is concentrated in the top layers and fall with the depth. The temperature gradient between relatively warm sea surface water and the colder one can be harnessed using ocean thermal energy conversion technology.
Figure below shows worldwide average ocean temperature differences in Celcius, between 20 meter and 1000 m water depth. The highest the differences, the highest the potential of OTEC is.
As mentioned above, OTEC utilizes warm seawater and cold seawater. The warm seawater is used to produce a vapor that acts as working fluid to drive turbines. The cold seawater is used to condense the vapor and to ensure vapor pressure differences drives the turbine.
That’s all I want to share. In the next post, I want to share about several technologies for each renewable energy resources and required capital cost and operational cost for each renewable energy resources.