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FAEPAC - Fundación Axencia Enerxética Provincial da Coruña

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Sea energy

The sea is with no doubt one of the biggest potential sources of energy at the moment, from its use as site for offshore wind farms to the use of tides and waves. It provides us with a future horizon full of expectations, even tough there isn’t a proper technological development at the moment.

In the province of a Coruña there are facilities that used this kind of energy since ancient times, such as the tidal mills of Acea da Ma, in Culleredo or the tidal mill of As Aceñas in Narón. In both cases the increase of the level of the water is used to set in movement the runner stones.

 

According to its use, the sea energy is divided into:

  • Tidal energy: based on the use of the difference of levels caused by the movements of the tides, between the high tide and the low tide. In both stages, there is a turbine placed strategically so that the flow of water makes it turn in order to produce electricity.

  • The biggest tidal power station was in France at the Rance estuary. It had a power potential of 240 Mw and it closed down after several decades working.

Wave energy: This type of use has different possibilities. One of the most common is the oscillating water column, where the movement of the waves pushes the air that gets pressured and expanded and therefore it can impel a turbine that produces electricity.

The biggest plant in the world is situated in Wizhinja (India) with a power potential of 150 Kw.

 Esquema dunha central de aproveitamento de enerxía das ondas (Fonte: INEGA)

Source: INEGA

Another kind of energy used is the one that uses superficial movement of tides using big cylinders to use the height difference produced between the wave crests in order to push the air that will move the turbines in order to produce electricity. There are some facilities of this kind in Europe, in Scotland and in  Portugal, being the last one the biggest with a power potential of 3 Mw in its first stage. This project will reach 24 mw (Pelamis project).

 

Use of thermal gradient of the sea. The temperature difference between the surface waters and the sea bottom may be more than 20ºC in a distance lower than 100m. Such violent changes in temperature are produced in tropical areas and they are softer in waters close to the equator.

This system is based on the condensation of gas in cold water and its evaporation in warm waters. In this process energy is freed.

Nowadays there  is a 1Mw plant in the coast of Hawaii and a similar one in the Japanese coast.



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