Marine energy play a key role in reducing CO2 emissions of human origin, so its momentum and development is crucial to mitigate the effects caused by climate change. Currently, the only technology that has reached a level of development sufficient to be competitive as offshore wind (offshore ). But there are other less developed systems that get energy from oceans and seas, such as using energy of waves (wave), the energy of the tides (tidal), the currents, the thermal gradient and the salt gradient.

The offshore wind energy (offshore) , with 2,063 MW installed at the end of 2009, is the most developed in the full range of marine renewable energies. Today the countries of northern Europe are leading the sector in the UK and Denmark in the lead. The main advantage of offshore wind farms located against the ground is that there are no obstructions that can reduce the wind speed, the usable resource is greater.

The wave energy is produced by the wave motion. Because wave energy is very irregular multiple prototypes have been developed able to harness its energy. Among them are the so-called first generation are characterized by being integrated into fixed fixed structures on the coast (cliffs breakwaters and dikes) or on the merits. The second generation are further away from the coast and in shallow water and can be treated or floating structures located on the bottom. Finally, third generation devices can be floating or submerged and are located in deep waters (up to 100 meters).

Currently various technologies are used to capture the energy of the waves. In the Oscillating Water Column ( OWC-Oscillating Water Column) wave movement raises and lowers the water level of a semi-submerged chamber and open at the bottom. This oscillatory motion causes the volume of air moving above water which generates an air flow able to drive a turbine.

These facilities are usually located near the coast or breakers, such as Mutriku project (Basque Country).

Other devices that harness the energy of waves are called absorbers or attenuators . In the first case it is floating structures capable of absorbing wave energy regardless of the direction of the waves. With wave movement device moves up and down, mechanical movement is then converted into electrical energy.

The attenuators are formed by large articulated partially submerged and connected by hinge joints cylinders.The wave induces a movement between said sections which activates a hydraulic system coupled to an electric generator.

However there are many other devices that can harness the energy of waves, such as systems overflow effect Archimedes(Archimedes Wave Swing-AWS) systems, impact or terminators.

On the other hand the tidal power for energy is the rise and fall of the sea caused by the tides. A water tank as a reservoir is filled at high tide and low tide empties, until a suitable level difference between the sea and the reservoir is reached. From this moment the water is passed through a turbine that generates electricity.

To make this technology cost effective today a jump of more than 5 meters tide, which only occurs in very specific places is needed. It also represents a significant environmental impact and the optimal locations are commonly found in estuaries or bays with great biological variety. The largest facility of this type is the centerpiece of La Rance in France which began operating in 1967 and produces annually 4,400 GWh with an installed capacity of 240 MW.

The ocean currents are also able to generate energy. Current technology is very similar to offshore wind but in this case the devices are submerged. The turbine rotor is mounted in a resting on the bottom or on a floating system structure. They would be required currents with speeds between 1 and 3 m / s for the profitability of the installation, which again limits the locations for this type of technology. Currently the greatest potential is in the UK.

Technologies Thermal Gradient ( Ocean Thermal Energy Conversion-OTEC) are able to take advantage of the temperature difference between the sea surface and the deep zones, ie what is known as ocean thermal gradient. A difference of more than 20 ° C temperature is required, so the equatorial and subtropical regions are most suitable for this type of energy.

It should be noted that despite its high potential research and projects are still at a preliminary stage. However experimental facilities in Hawaii, India and Japan have done. These include the floating platform installed in India in 2001 with a power of 1 MW.Sagar said platform called shakti (Sanskrit, “the power of the ocean”) was launched by the National Institute of Ocean Technology of India and Saga University (Japan). It is located 40 kilometers off the coast of Tamilnadu and is a floating platform that uses collected water to 1,000 meters deep.

Lastly technologies are osmotic pressure (also called Blue Energy) and Gradient Salino .

The first one is based on the phenomenon of osmosis, so they are able to take advantage of the difference in pressure between freshwater and salt water to produce energy.

Norway’s state energy group Statkraft has inaugurated the first prototype in the world of this type of technology, located in the Oslo fjord.

In the case of salt gradient energy is obtained by the difference in salt concentration exists between seawater and river water. When fresh water mixes with salt water a release of energy that could theoretically be exploited occurs.

It is important to recognize the high potential of this technology though is still underdeveloped and its cost is still very high.