Marine energy

Overall, marine is one of the most promising renewable and non-polluting energies available at the moment, and is expected to be Europe's main source of energy by 2040. ​ Although we usually refer to it in the singular, there are different ways of harnessing the energy generated by the sea, whether through waves, tides, salinity or temperature differences. Thus, in general, marine energy is one of the most promising renewable and non-polluting energies available at the moment, and forecasts indicate that, by 2040, it will be the main source of energy in Europe, according to the WindEurope platform.

This form of renewable energy has great potential. Current production is around 12 GW, but the forecast is that production will reach 60 GW by 2030 and 300 GW by 2050, as part of an ambitious European plan to reduce greenhouse gas emissions to achieve climate neutrality by the middle of the 21st century.

Apart from the fact that the sea, as a resource, can produce energy virtually constantly and is generally clean and very quiet, thanks to the higher density of water, this energy can be obtained at speeds as low as 1 m/s. However, in order to get the most out of it, an investment of more than 800 billion euros in network and production infrastructures will be necessary.

As we said earlier, there is no single way of harnessing energy, and depending on the characteristics of the coasts, one or several production systems can be adopted, including hybrid models.

Tidal energy: energy production is based on taking advantage of the rising and falling movements of the tides, and can generate energy in both ways, although this method is only really effective in those places where the low tide and high tide points are at least five metres apart. In the few places on the planet where it is possible to harness the potential of the tides, three different types of power plants can be installed:

• The TSG or Tidal Stream Generator works with a system very similar to wind turbines, which has a low ecological impact and a lower cost than other methods.

• The tidal barrage is a dam-like structure that holds back water from the rising tide and works in a similar way to hydroelectric power plants. This system, however, has a high economic cost and a greater environmental impact.

• DTP or Dynamic Tidal Power would alternate the two systems above, inducing the retention of tidal water and using it to drive the turbine generators. However, it would require, apart from the special tidal conditions, a coastline of between 30 and 50 km in length on which to build the dams.

Current energy: in this case, the kinetic energy of ocean currents is harnessed, and this is done by means of a system of underwater converters that is similar to that of wind turbines.

Thermal energy: this is based on the use of the so-called "Rankine cycle", based on the temperature differences between the sea surface and the depths, and is particularly efficient when the gradient is at least 20º. The operation is similar to that of a steam thermal power plant.

Wave energy: it captures the energy produced by the movement of the waves, which in turn is produced by the wind. The energy obtained by this system is used for generating electricity, desalinating water or pumping it.

Salt gradient energy: also called "blue energy", it is based on the differences in the salt concentration gradient between seawater and river water, using various methods such as delayed pressure osmosis or reverse electrodialysis.

Given the relatively recent development of these systems, some of them are still in the testing phase, and it is possible that, over time, the use of materials and space needed to install these plants will be optimised. For this very reason, their "youth" as an energy source, there are questions that we are not yet able to answer, such as how the installations will affect marine ecosystems in the medium and long term. Moreover, since they will be located in the sea and not on land, maintenance costs are likely to be higher.

Fátima Gordillo