Marine Energy: Unlocking the Power of the Seas

A renewable energy source with high potential but still little exploited

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By Alex

marine energy

In the quest for sustainable energy sources, marine energy has emerged as a promising frontier. Harnessing the power of the seas offers a renewable and abundant alternative to conventional fossil fuels. This essay explores the various forms of marine energy, their production methods, advantages, and disadvantages, shedding light on the potential of marine energy to reshape our energy landscape.

What is Marine Energy?

Marine energy encompasses the renewable energy derived from the ocean’s resources, including waves, tides, currents, and temperature differentials: this energy is later converted into electrical or mechanical energy. It represents a vast and largely untapped source of clean energy that holds the key to reducing carbon emissions and mitigating climate change.

To harness it, facilities are needed that channel these forms, whether they be waves, currents, tides, or temperature differences recorded at different depths of the water, allowing kinetic energy to be extracted for various applications.

However, currently, these technologies are not yet applicable on a large scale, and above all, they have not yet reached a level of development that would allow them to be used on a large scale. This is also because very complex and environmentally impactful infrastructures are required.

In fact, the exploitation of marine energy is still in the experimental phase, despite numerous experimental projects being active.

How is Marine Energy Produced?

The production of marine energy involves various technologies tailored to harness specific marine resources. These methods can be categorized into wave energy, tidal energy, current energy, thermal energy from the sea, and saline gradient or osmotic energy.

Wave Energy

Wave energy exploits the kinetic energy generated by the motion of ocean waves.

The most well-known and utilized mechanism for storing energy produced by waves is based on oscillating water column generators that capture incoming waves on the coast. In practice, water enters a cylindrical chamber where there is air above the water surface. The arrival of the wave causes the water level to rise, compressing the air above. Both on entry and exit, the water drives a turbine.

However, utilizing this type of renewable energy on a large scale is not straightforward:

  • The challenge lies in using mechanical systems and properly anchoring them in a very turbulent environment.
  • There is corrosion of submerged equipment.
  • There is a significant environmental impact both from onshore and offshore installations, which can affect marine biodiversity.
  • There is a strong variation in intensity over time: during calm days, it is almost negligible, but during storms, it can reach hundreds of kilowatts per meter of coastline.
  • Installing and maintaining structures at sea is difficult, costly and dangerous.

marine energy

Tidal Energy

Tidal energy is a renewable energy source that capitalizes on the gravitational pull of the moon and the sun on Earth’s oceans. This force creates tidal movements, which are harnessed using various technologies such as tidal barrages, tidal stream generators, and tidal turbines.

Tidal barrages, for instance, utilize the rise and fall of tides to generate electricity by directing water through turbines. Tidal stream generators and turbines, on the other hand, capture kinetic energy from the continuous flow of tidal currents. These technologies play a significant role in generating clean electricity by converting the natural ebb and flow of tides into a sustainable power source.

Current Energy

Current energy, also known as marine or ocean current energy, taps into the kinetic energy present in ocean currents. Specialized turbines positioned strategically in areas with strong currents capture this energy, similar to how wind turbines operate underwater. As ocean currents flow continuously, these turbines spin, generating electricity.

This form of marine energy holds immense potential, particularly in regions with powerful currents, offering a consistent and reliable source of renewable energy. By harnessing the natural movement of the oceans, current energy contributes to reducing dependence on fossil fuels and mitigating climate change.

Thermal Energy from the Sea

Thermal energy from the sea exploits temperature differentials between the warm surface waters and the colder depths of the ocean. Ocean Thermal Energy Conversion (OTEC) systems utilize this temperature gradient to produce electricity. The process involves using a working fluid with a low boiling point, such as ammonia, which vaporizes when exposed to warm surface waters.

The vapor drives a turbine connected to a generator, producing electricity. The vapor is then condensed using cold seawater from deeper layers, completing the cycle. OTEC systems have the potential to generate clean and consistent electricity, particularly in tropical regions where temperature differentials are significant, contributing to the diversification of renewable energy sources.

Saline Gradient or Osmotic Energy

Saline gradient or osmotic energy harnesses the osmotic pressure difference between freshwater and saltwater to produce electricity. Membrane-based processes such as Pressure-Retarded Osmosis (PRO) or Reverse Electrodialysis (RED) are employed to exploit this gradient. In PRO systems, freshwater and saltwater are separated by a semi-permeable membrane.

As freshwater naturally flows into the saltwater due to osmosis, pressure builds up on the saltwater side, which is then used to drive a turbine and generate electricity. Similarly, RED systems utilize ion-selective membranes to create a voltage difference between freshwater and saltwater, which can be converted into electrical power. Saline gradient energy holds promise as a renewable energy source, particularly in coastal areas where freshwater and saltwater meet, offering a sustainable solution to energy generation.

Advantages of Marine Energy

Marine energy offers several advantages over conventional energy sources. It is renewable, abundant, and highly predictable, as oceanic phenomena like waves, tides, and currents follow natural patterns. Moreover, marine energy production has minimal environmental impact, emitting no greenhouse gases or pollutants during operation.

However, as mentioned earlier, marine energy is not yet used to power homes because the necessary infrastructure and facilities to harness it on a large scale in an economically viable manner are lacking.

Here are the benefits of this renewable energy, especially if a way could be found to utilize it more easily at low costs:

  • It represents a clean, abundant energy source.
  • Many installations are non-invasive, thus having a low environmental impact.
  • It’s a significant resource quantitatively, since oceans cover approximately 70% of the Earth’s surface.
  • It can be harvested and utilized through various methods.
  • It can be fairly accurately planned by studying wave strength, making it a predictable form of renewable energy.
  • It reduces dependence on oil.
  • It potentially allows for the production of very high amounts of energy. To give an idea, near the shore, power density ranges from 30 kW to 40 kW per meter of wave; as one moves offshore into deeper waters, power density increases to about 100 kW.
  • It can also be harnessed in open seas through offshore power plants.
  • Moreover, it is precisely in open seas where the potential of waves increases.

Disadvantages of Marine Energy

Despite all the undeniable benefits, generating electricity through harnessing wave motion, tides, marine currents, and exploiting temperature differences in water at various depths is a rather complex and costly process.

Challenges include finding the most suitable areas to install the facilities, as well as the high costs involved in construction and management. Moreover, there are risks to the marine ecosystem: noise generated by some machinery can disturb various marine species, thus altering aquatic habitats. Performance may also be limited in adverse weather conditions.

Coastal landscapes can be marred by the installations, which can also create noise pollution affecting coastal communities and disrupt shipping (cruise, private, commercial, cargo) and maritime activities.

Did You Know That…?

  • The largest tidal energy plant is located in South Korea and has a capacity of 254 MW.
  • Currently, the only operational tidal power plant is in France: in Saint Malo, at the mouth of the Rance River. Built in the 1960s, it harnesses a very large tidal range, which can reach a difference in level of 13.5 meters. The maximum power output is 240 MW, while the flow reaches 18,000 cubic meters of water per second. This plant covers 3% of Brittany’s electricity needs.

Conclusion

In conclusion, marine energy holds immense potential as a sustainable and environmentally friendly alternative to traditional fossil fuels. By tapping into the vast energy resources of the oceans, we can mitigate climate change, reduce reliance on finite resources, and foster a more resilient energy infrastructure. However, realizing this potential requires continued research, innovation, and investment to overcome technical and economic barriers and ensure responsible stewardship of our marine environments.

As we navigate the transition towards a cleaner energy future, marine energy stands poised to play a crucial role in powering our world sustainably.

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