Optimizing Wave Energy Converters as a New Renewable Energy Source for Indonesia

Earth is a planet where 70% of its surface area is composed of water while the rest 30% of the Earths surface is composed of land. However generating electricity using ocean energy is still miniscule compared to the usage of fossil fuel sources, which contributes to most of the air pollution we have today. In this current modern era that we’re all experiencing, the most common way of generating electricity in Indonesia is by using conventional methods where the fuels used are comprised of coal, oil and natural gas. The rapid rise in fossil fuel combustion has produced a corresponding rapid growth in CO2 emissions and accounts for over 80% of global anthropogenic green house gas emissions (GHGs) in 2008 alone. Based on REN21’s 2017 report, renewables only contributed 19.3% to humans’ global energy consumption while 24.5% to their generation of electricity in 2015 and 2016. Thus we need to actively take part in finding new ways of generating clean and renewable energy; one way to do it is to go to the sea which Indonesia is widely known for. Fortunately there is a good news for wave energy enthusiasts, according to the IEA-OES, Annual Report 2007; wave energy has an annual global potential of 8000 to 80000 Terawatts-hour per year and this source contributes to the majority of any kind of ocean energy related power generating systems compared to tidal current, salinity gradient and OTEC developments.

Status of Technology Development in Ocean Energy. Source: IEA-OES Ocean Energy Systems.

Therefore we need to find a way to get these new technological advancements and methods to be effectively implemented, taking into account that Indonesia is a massive maritime nation and has the 2nd longest coastline worldwide behind Canada with a coverage of 54,716 kilometers. Indonesia, where three quarters of its sovereign territory is comprised of water, has 49 GW recognized potential ocean energy with an addition of 727 GW theoretical potential ocean energy. This is a critical reason as to why Indonesia needs to increase its role in optimizing ocean energy as a fresh source of renewable energy to steadily decrease its consumption and extreme dependency of using fossil fuels. Now we will move on to dive deeper into details about our main topic, wave energy converters.

Wave energy converters (WECs) are devices that convert the kinetic and potential energy associated with a moving wave into mechanical energy therefore generating electricity. Waves have a huge potential in providing a completely sustainable source of energy as waves never stop moving and existing, therefore it can be harvested at any time. Wave energy converters can be separated into seven different types:

  1. Point absorbers.
Vertical Motion of a Point Absorber in Implementation
Construction of a Point Absorber

Point absorbers are a floating structure that have a small horizontal dimension compared with their vertical dimension and utilize the wave action at a single point. This structure enables it to absorb energy through the vertical motion of its top part at the surface that follows the up-and-down movement of the ocean waves. It converts the motion of the buoyant top relative to the base into electricity. Point absorbers are the most common wave energy converter archetypes available with 58 devices around the globe and it is one of the most prevalent design archetypes in the ocean energy sector to date.

2. Attenuators.

Movement of an Attenuator Relative to the Ocean Waves

An attenuator is a floating device which operates parallel to the wave direction and effectively rides the waves (mimics the shape of the wave below the device). These devices capture energy from the relative motion of the two arms as the wave passes them. They are usually modular in design and rely on the flexing of joints to generate power. The common wavelength is an important consideration for these designs so it is important to know the wave’s behavior in that particular area so that maximum power can be secured from a given wave characteristic.

3. Overtopping or Terminator Devices.

Generic Overtopping Device
Wave Dragon Overtopping Device Power Take-Off

Overtopping devices utilize a difference in potential energy by raising a volume of captured water as waves run-up a ramp and break into a storage reservoir which is at an elevation higher than the surrounding sea level. An overtopping device may use ‘collectors’ to allow water to enter and thus concentrate the wave energy into a waterway. With the help of gravity, the water is then returned to the sea passing through a conventional low-head turbine which generates power.

4. Oscillating Water Column.

Generic Oscillating Water Column

An oscillating water column is a partially submerged and has a hollow structure. It is open to the sea below the water line, enclosing a column of air on top of a column of water. As waves pass-by underneath the machine, it causes the water column to go up and down, making their reciprocating motion acts similarly to a piston in the chamber, raising and lowering the pressure inside. This trapped air is allowed to flow to and from the air through a turbine, this turbine is able to rotate in the same direction regardless of the direction of the airflow. The rotation of the turbine is then used to generate electricity.

5. Oscillating Wave Surge.

Generic Oscillating Wave Surge Device
BioPower’s bioWave Device

This archetype design of wave energy converters takes advantage of the ocean’s surge of waves which moves the ‘flap’ in a horizontal direction. The bottom part of these devices are generally placed fixed on the ocean floor with the top part or the ‘flap’ acting like a pendulum that pivots on a hinged joint as surge waves pushes it, causing it to oscillate back and forth. The flap’s movement is then optimized and the device is later connected to an electric generator, thus producing electricity.

6. Submerged Pressure Differential.

Submerged Pressure Differential Moves Relative to the Ocean Waves

This type of wave energy converter relies on the pressure fluctuations created by waves as it passes over the machine. The way this device works is that the motion of the waves causes the water level above the device to continuously go higher and lower to a certain frequency. When the water level reached its peak, it creates a pressure against the device, therefore pushing it downwards and vice versa. This allows the semi-floating ‘buoy’ to oscillate in a vertical manner. This device can be built near the seafloor or it can also be built similar to a point absorber but submerged below the ocean surface. The lower part of both of these types are fixed in to the seabed, whilst the buoyant are able to move freely to be able to turn the turbine and generate electricity.

7.Rotating Mass.

Rotating Mass Device
Wello Oy’s Penguin Device

Rotating mass wave energy converters are commonly known as floating riders that utilizes an internal weight which is placed on a fixed point that can rotate to drive an electric generator. The motion of the ocean waves causes the device to sway and heave, consequently making the hull’s center of buoyancy and gravity to shift periodically. In addition to that, the weight/mass (Either an eccentric weight or a gyroscope) inside the device is constantly rotating as it tries to reach equilibrium.

To conclude, wave energy converters are useful in various ways to generate clean and renewable energy for human’s increasing demand in energy consumption, especially for a maritime nation like Indonesia and other maritime nations. In addition to that, according to Ocean Energy Europe (2013), it estimated that there will a potential of creating 20000 jobs all over the marine energy sector in the year 2030. If implemented correctly, this will easily allow Indonesia to decrease its unemployment rate and improve its ocean energy sector at the same time.

Source:
https://theliquidgrid.com/marine-clean-technology/wave-energy-converters/#:~:text=Wave%20energy%20converters%20(WECs)%20are,useful%20mechanical%20or%20electrical%20energy.

https://setis.ec.europa.eu/system/files/Technology_Information_Sheet_Ocean_Energy.pdf

Usenobong F.Akpan. 2011. “The Contribution of Energy Consumption to Climate Change:A Feasible Policy Direction”. University of Uyo.

Jochen Bard. Ocean Energy Systems Implementing Agreement an Intenational Collaborative Programme. IEA-OES Ocean Energy Systems.

REN21 Global Status Report 2017

https://www.youtube.com/watch?v=WToY7tzdHCE&t=1s. TU DELFT — Wave Energy.