Wave energy and its different elements of understanding
Wave energy is a renewable energy that uses the strength of swell’s ripple or the strength of breaking waves on coasts, to convert them into electricity thanks to wave energy systems.
The energy potential of wave energy :
The World Energy Council confirms that wave energy has an exceptional energy potential in the global energy mix, given that 71% of the planet’s surface is covered by seas and oceans. Yet, this energy is still largely untapped.
Many organizations tried to evaluate the energy potential of wave energy, but didn’t conclude to the same results, based on different ways to calculate. Indeed, the International Energy Agency estimates that the energy potential of wave energy is between 8,000 and 80,000 TWh per year, whereas EDF Pulse Venture estimates that this energy has a global energy potential of around 5,000 TWh per year.
Nevertheless, when the organizations use smaller scales to evaluate the energy potential of wave energy, for example on the European level, the results are quite similar. For example, the capacity of electricity production from wave energy is estimated to be around 150 TWh per year. Another example, the potential for electrical energy from wave energy in Great Britain is estimated at 50 TWh per year, which is equivalent to the annual production of five nuclear reactors.
Main wave energy systems :
Among wave energy systems, designed to exploit the energy of waves, five have stood out : vertically oscillating columns, water columns, surge systems, floating systems and submerged systems.
Vertically oscillating columns are floating structures, most often these are buoys. They are installed on the surface of the water and are connected to the seabed by a piston. These buoys use swell’s ripples, its vertical and horizontal movements, to activate the piston. This piston exerts pressure on a hydraulic fluid which turns a turbine, driving an alternator that generates electricity. The « Wavebob » wave energy system is the perfect example of vertically oscillating columns.
Water columns are floating (at sea) or fixed (on the shoreline) structures that look like large « boxes » with only one side opening facing the wave. Through this opening, waves rush into the column and expel the air trapped in the column. This opening enables waves rushing into the column to expel the air trapped there. The air pushed by the engulfing waves passes through turbines located at the top of the water column. Next, when the column empties of its water after the wave has passed, the drop in pressure in the column sucks in air from outside and turbines are pressed in the other direction. The « Limpet » (Land Installed Marine Powered Energy Transformer) is an example of water columns.
Surge systems (offshore or fixed on the coast) are based on the filling, by breaking waves on artificial ramps, of a reservoir raised above sea level. To empty this reservoir, the water trapped in it is turbined via turbines. Then, the turbines will turn an alternator which generates electricity. The « Wave Dragon » illustrates offshore surge systems and the « Tapchan » is an example of a surge system fixed on the coast.
Float systems are long floats which are attached to each other. They are kept on the surface of the water and stowed to the seabed in the direction of the wind and installed perpendicular to the waves. Wave movements cause these floats to oscillate which will compress a hydraulic fluid, and by that actuate a turbine generating electricity. The best-known and most publicized float system is the « Pelamis » or « sea serpent ».
Submerged wave energy systems are underwater and fixed to the seabed. They use the oscillation of the swell or waves to set these submerged bodies (buoys or walls) in motion. The movement of these systems actuate pumps which compress a hydraulic fluid driving a turbine. The « Oyster » prototype and the « CETO » prototype are examples of submersible wave energy systems.
Difficulties and disadvantages obstructing the operation of wave energy installations :
Wave energy systems face various difficulties and disadvantages.
Initially, wave energy systems has been tested must withstand severe weather conditions such as storms. Nowadays, no wave energy system can withstand extreme natural events. Moreover, wave energy installations are quickly damaged by corrosion due to the salinity of the seawater.
Then, equipment and installations are very expensive. Many costs need to be considered (the cost of initial materials, the cost of transportation, the cost of installation, the cost of the electrical connection, the cost of exploitation and maintenance). All these high costs prevent the efficiency and economic viability of wave energy systems.
Subsequently, wave energy systems can form environmental problems due to their physical presence and operation. Indeed, wave energy systems can collide with fish, disrupt the migration of certain fish species, modify the topography of the seabed, and generate chemicals, noise, and electromagnetic pollution.
Finally, wave energy developments can disrupt uses from the seas and oceans such as fishing activities, cruises, or maritime transport activities. These latter disadvantages can be barriers from the point of view of social acceptability.
Thus, wave energy can be a major asset to decarbonize the energy mixes of countries with coastlines. However, technological progress still needs to be made to make wave energy systems economically viable and environmentally acceptable.
