The search for renewable energy
The challenge today is to find alternative solutions which are more sustainable and less harmful for the environment to provide the energy we need for our activities.
To do that, we need to encourage societies to move from the consumption of mainly non-renewable energy towards non-destructive and sustainable consumption. It is essential that this shift from one method of production to another is also accompanied by more mindful consumption. This process to transform the relationship between people and energy is called the energy transition.
One solution for this transition involves producing energy which does not consume finite resources. This is called renewable energy, an example of which is energy harnessed from the sea.
What is “Marine Renewable Energy”?
The ocean, due to the numerous natural phenomena which interact in it, represents an inexhaustible source of energy which can be exploited: currents, waves, wind and tides as well as temperature and salinity gradients. Marine Renewable Energy (MRE) is now undergoing significant development, justifying the hopes placed in it. There are five types of MRE in its true sense, meaning that it derives its energy production from the dynamics of the oceans, the natural movements of ocean water masses:
• Hydrokinetic energy: energy generated by the movement of ocean and river currents
• Ocean wave energy: mechanical energy of surface waves and potential energy of swell
• Tidal energy: energy produced by the movement of water due to tides
• Thermal energy: energy created by the difference in temperature between the water masses at the surface and at greater depths
• Osmotic energy: energy based on the difference in salinity between fresh water and seawater
Other types of energy may be harnessed at sea but aren’t strictly produced by water:
• Offshore wind power which uses the wind found over the oceans to create energy.
Offshore wind power is often included as a type of Marine Renewable Energy. There are two techniques:
o Fixed foundation offshore wind turbines which are attached to the ocean floor,
o Floating foundation turbines which are fixed to a platform floating on the ocean’s surface.
Note that biomass energy, such as the use of seaweed to produce biofuels, is not considered to be a type of Marine Renewable Energy.
Barriers to the development of Marine Renewable Energy
Several technical challenges have so far hindered the development of Marine Renewable Energy, notably the need to transport the energy produced to the electrical grid and the need to be able to store the energy.
Transporting energy
Energy produced at sea needs to be transported long distances and consequently part of the energy is lost. Infrastructure close to the coast therefore offers an advantage compared to that located further offshore, far from where the energy will be used.
Energy storage
Some methods work ‘intermittently’. A more favourable way of putting it would be variable, discontinuous and unprogrammable energy production. The production of this energy depends on external factors (swell, wind, current, tides) which do not allow controlled and uninterrupted production. The energy is not produced in line with energy requirements, but is dependent on these external factors. Surplus energy may be produced. In this case, it needs to be stored. However, it’s difficult to store energy without some of it being lost. Nevertheless, current technologies are progressing rapidly and, although batteries have always been seen as the obvious method for storing energy, there are other solutions.
One technique in particular has demonstrated its potential: the Pumped-Storage Power Plant. For this method, two reservoirs of water are required. When there is an energy surplus, water is pumped to the higher elevation reservoir. When energy demand increases or when less energy is being produced, the water from this reservoir is released to the lower reservoir and creates energy by activating turbines. This enables the balance between production and consumption to be maintained on the electrical grid. Effectively, intermittency is not a problem but rather a context to be managed.
How a Pumped-Storage Hydroelectricity works
Advantages and disadvantages of each type of Marine Renewable Energy
Each type of Marine Renewable Energy presents advantages and disadvantages. All the different parameters must be taken into account when deciding on their installation in order to choose the most suitable solution depending on the place, production potential and energy requirements.
Comparative table of the different types of Marine Renewable Energy:
