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What is Ocean Wave Energy Harvesting ?

Harvesting ocean energy involves capturing the kinetic, thermal or chemical energy from the ocean and converting it into usable forms of energy, such as electricity. There are various technologies and methods for harnessing ocean energy, depending on the specific type of energy source you are targeting. Some of the primary methods used to harvest ocean energy include tidal energy, wave energy, Ocean current energy, ocean thermal energy and salinity gradient energy, Let us understand Ocean Energy harvesting system used to generate electricity, its working principle, advantages and disadvantages.

Wave power captured from ocean waves has many applications which include electricity generation and distribution, water desalination, pumping of water etc. Many countries inluding USA, UK, Canada, Australia, New Zealand are supporting development of ocean energy based systems.

How to harvests ocean energy ?

This renewable energy source is generated primarily from the movement of water, such as tides, waves, ocean currents, and temperature gradients. Ocean energy has the potential to provide a consistent and reliable source of clean energy, helping to reduce greenhouse gas emissions and reliance on fossil fuels. The Ocean Energy is better than other renewable energies as it is available 24/7 on 365 days where as Wave energy contains about 1000 times kinetic energy of wind. Wave energy has highest energy density among all renewable energy sources.

There are several key technologies for harnessing ocean energy which include tidal energy, wave energy, Ocean current energy, ocean thermal energy and salinity gradient energy as described below.

1. Using Tidal Energy

Tidal energy is generated by the gravitational pull of the moon and the sun, causing the rise and fall of tides. Tidal energy can be captured using tidal stream systems, tidal range systems, or tidal lagoon systems. Tidal stream systems use underwater turbines to capture the kinetic energy of moving water. Tidal range systems, on the other hand, rely on the height difference between high and low tides to generate energy. Tidal lagoon systems involve creating artificial lagoons to capture and release water as the tides change.

2. Using Wave Energy

Wave Energy is generated by movement of surface of the ocean waves back/forth and up/down. This energy is captured and converted to electrical power. This wave energy has capability to provide 10% of energy need of the entire world. Various technologies, such as point absorbers, oscillating water columns, and attenuators, are used to capture the energy from waves. These devices typically involve the movement of buoyant structures that drive generators as they move with the waves.

Ocean Wave Energy conversion system

As shown in the figure, as the wind passes over ocean surface, its kinetic energy is transferred to the water which forces water to pass through the turbine generator. The force of water on blades rotates the rotor shafts of this turbine generator. As a result, generator converts mechanical energy (i.e. kinetic energy) to the electrical energy. As described above, various Ocean Energy conversion devices are used for such wave power based system as per their performances and application requirements.

As shown in the figure, different types of devices are used for Ocean Energy harvesting as per application requirements. This includes surface attenuators, overtopping system, Point absorbers, Oscillating water column, oscillating wave surge converter, tidal energy etc.

Ocean Energy Harvesting Methods

Attenuators : These devices are installed perpendicular to length of the sea waves. Several such sections are connected using joints which allows attenuators to undulate along movement of waves. Hydraulic cylinders (i.e. pumps) are being pulled due to wave movements which causes compression of fluids. This action creates electrical current.
Overtopping : This technology is similar to hydro-power dam. The design allows water to be collected at the center called reservoir where water is stored. These water is made to pass through the several hydro turbines. The pressure of the water spins the turbines which causes ocean energy to be converted into electrical energy. Magnetic generator based overtopping system can withstand environmental hazards.
Point Absorber : This technique uses a device called "buoy" which floats above the ocean water and moves up and down as per movement of waves which causes electric power generation. Multiple such units are installed as per electricity requirements.

3. Using Ocean Current Energy

Ocean currents, such as the Gulf Stream, can be harnessed to generate electricity. Devices like underwater turbines are placed in these currents to capture the kinetic energy of moving water.

4. Using Ocean Thermal Energy

Ocean thermal energy exploits the temperature difference between the warm surface water and the cold deep water of the ocean. This temperature gradient can be used to drive a heat engine, typically in the form of a closed-loop system with a working fluid like ammonia.

5. Using Salinity Gradient Energy

Also known as blue energy or osmotic power, this technology utilizes the difference in salt concentration between saltwater and freshwater to generate electricity. Membrane-based processes and pressure retarded osmosis (PRO) are some of the methods employed for this purpose.

The other techniques used to harvest oceanwave energy are Offshore Wind Energy, Hydrokinetic Energy, Vortex Induced Vibrations, Bioenergy from Marine Organisms, Piezoelectric Materials, Hydraulic Energy Storage, Hydrothermal Vent Energy, Biomechanical Energy, Wave Reflectors, Underwater Kites and so on as per ongoing research and experimentation in this field.

Benefits or advantages of Ocean Energy harvesting

Following are the benefits or advantages of Ocean Energy harvesting:
➨The energy produced here is renewable as wave energy will never run out unlike fossil fuels.
➨This technique does not create harmful by-products such as waste, gas, pollution etc. It produces very little environmental impact which is not visible from shore.
➨The system is not expensive to maintain.
➨The energy produced is free for use.
➨Wave power is nearly unlimited and more predictable compare to wind and sun based power systems.
➨The wave power system produces great amount of electrical energy which is very useful to the power consumption of the large part of the world population.

Drawbacks or disadvantages of Ocean Energy Harvesting

Following are the drawbacks or disadvantages of Ocean Energy Harvesting:
➨Power plants and areas near the ocean can only benefit using this technique.
➨It will have effect on marine ecosystem.
➨The electricity generation is random and not continuous. Hence Ocean Energy technique requires site where waves are always strong in order to get continuous electricity generation.
➨The system should sustain very rough weather conditions in order to be functional.

Conclusion : Benefits of ocean energy harvesting include its predictability and reliability compared to some other renewable sources like wind and solar. However, there are challenges to overcome, such as the harsh marine environment, high upfront costs, and potential environmental impacts on marine ecosystems. Research and development efforts are ongoing to improve the efficiency and reduce the environmental impact of ocean energy technologies.

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