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About wave energy conversion (April 2022) Wave energy conversion is another type of system for replacing fossil-origin power. Its promoters often complain that, similarly to tide energy, it is insufficiently promoted despite that it offers a better availability than wind power as waves and swell last a long time after being created and can come from very far. Even though humans were capable of fighting the effect of waves to create ports and protect sensitive parts of the coasts since before antiquity, recovering their energy was challenging because, opposed to tidal currents and wind, which are continuously flowing when established, the energy from the waves and the swell is cyclic, which made it difficult to convert it into usable power with the technologies available during these periods. Pierre Simon Girard (1765-1836), a reputed French engineer and scientist, is considered the 1st known inventor of such machines, with a patent published in 1799.. However, steam machines using wood and coal became available at the beginning of the 19th century, which made the use of cyclic energies economically obsolete during this time due to the low cost of coal and the possibility to use steam power 24/7. Gas and oil replaced coal for many applications at the beginning of the 20th century due to their availability, ease of use and storage, and low cost during this period. For this reason, converting wave movements into energy came back into consideration only when governments started to look for cheap and renewable sources of power following the rise of oil and gas prices in 1973, and more recently with the highlighting of the greenhouse effect, attributed to the overconsumption of fossil-origin energy. As a result, engineering offices have proposed new concepts that can be roughly classified as indicated below (Click on the pictures to open the animations), and several pilot power plants were created to verify the feasibility of various technical solutions. Of course, consider that engineers are usually inventive people and that concepts that merge the solutions presented above or based on new ideas are regularly proposed.

• Some systems consist of chambers with the bottom side opened. The waves enter and exit these chambers and act as pistons that compress the air contained in them to a one-way turbine activating a generator. These chambers can be made of steel or composite materials and be installed on a floating device or made of concrete built on a jetty or a favorable part of the coast.

The system above, designed by Havkraft technology, is planned to be installed on a specific barge anchored off the coasts.

The system above, promoted by Voith, uses the same principle as the one designed by "Havkraft technology", except it is made of concreate and built on the shoreside.

The system above from "Wave Swell Energy" is a variation of the principle previously described that consists of organizing the air that passes through the turbine, and activates the generator, only when the wave draws it into the chamber during its moving down phase. Thus valves are installed to expel the air compressed in the room when the wave comes up without activating the turbine. These devices are positioned on the seabed in direct proximity to the shore. The promoters say that such a design increases the durability of the turbine.

• Another family of solutions consists of a floater, linked by a solid arm to a static frame and a mechanism composed of gears, or hydraulic cylinders, or an arrangement of both that activate a generator when the waves' movements cause the floater to heave up and down. Such systems can be installed on offshore platforms or other static supports such as jetties.

As an example of the numerous solution adopted by engineers who selected this process, the system above from "CNA Meccanica Srl" uses only gears to transform the movements of the waves into electricity.

Purely hydraulic systems can be illustrated by the system above, designed by "Wave water works", where the arm's movement activates hydraulic cylinders that set a motor that rotates the generator in motion. This principle is utilized by many manufacturers such as Wave star A/S in Denmark with the testing project "Wave star energy" below (stopped in 2016), or "Ecowave power" project in the UK, which principle of work is explained underneath.

A variation of hydraulic systems powered by a floater and an arm is the one currently used in the “Usina de Ondas do Pecem (Pecém Wave Plant)” in Brazil where the movements of the buoy activate hydraulic pumps, which compress the freshwater contained in a closed circuit by means of an accumulator, and then jet it against the blades of a water turbine situated in a hyperbaric chamber from which this water is pumped again (See in the animation below).

• A third family of wave energy convertors consists of an anchored buoy that follows the movements of the waves. The mechanism that produces electricity is housed in the buoy. It consists of a bidirectional electrical generator activated by a piston and springs. An electrical cable is connected to the bottom of the buoy to transfer the electricity produced to the network. It can be represented by the “CorPower Ocean” system below.

• Another interesting system consists of a modular anchored floating carpet that undulates with the waves and which undulations activate levers that in turn activate cylinders that push and draw a hydraulic fluid that rotate a generator through a hydraulic motor. The system below, designed by “Sea Wave Energy”, is a good representation of such a solution.

• As already discussed, engineers' inventiveness may result in other solutions that combine some of the above principles. It is the case of systems like the one below from Weptos A/S, composed of a series of self-buoyant rotors, whose rotation around their axis activate generators through belts and gears. These items are solidarized on a chassis in a V shape whose angle is automatically adjusted according to the hardness of the sea to provide an optimistic yield without damaging the installation. This arrangement is fastened to a mooring buoy and pivots around it to adjust to the direction of the waves.

Like tide and wind turbines, it is too early to say which systems will be the most successful. There are many elements that must be considered to decide that. Also, the systems presented must be seen as complementary solutions as some are more appropriate to some situations than others. They also must be seen as complementary solutions of tide and wind turbines as it is not ridiculous to organize fields where these three systems are working together. It is also probable that if such systems are massively adopted, the available areas along the shore will be quickly occupied, and that the solution will be to install them offshore. Regarding the diving activities that may arise from such installations, it seems that underwater maintenance activities of such systems are interventions such as inspection of the mooring lines, cleaning, and eventually the recovery and reinstallation of floating devices. It must be noted that the installation of many floating systems should require deploying dedicated anchor systems and burying and protecting the electric cables coming to the shore. Regarding the systems built on the coast, the diving activities will probably be limited to activities such as the inspection of the cofferdam. A periodic review of the foundations should also be organized every year. As for the previous topics, a list of dedicated papers that can be read to understand this market is available through the link below. The documents are classified by date of publication Click on the descriptions to open them