Last frontiers of renewable energy from the sea

This article is taken up the issue of the exploitation of water as a source of energy and, today we face the issue of the exploitation of wave energy as a source of energy.

 

THE SWELL

The waves are formed due to the action of the wind, dragging along its direction the surface layer with which it is in contact, and due to the viscosity of the fluid which leads to the transmission of this "drag" of the wind toward the inner layers of the water in examination carrying a "landslide" of the surface.

Another cause of the wave motion is attributed to ocean currents which lead to the mixing of the mass of water due to the gradients of temperature and salinity present in it.

Cause "extreme" are the telluric phenomena and the posting of glaciers, although they may lead to the formation of waves of size and energy capable of operating the destruction that we know, and that by their very nature "abnormal" is not of interest for the purpose of this post.

ENERGY EXTRACTION FROM THE SWELL AND THE CURRENT

The water, by virtue of its density represents an energy resource and its exploitation for different systems have been proposed and tested over the years.

It 'important to distinguish first of all between methods that aim to exploit the wave and methods that take advantage of the currents.

An example of a system that exploits the wave motion is represented by Pelamis project, which exploits the sinusoidal oscillations of the waves (and therefore the oscillations reciprocal of the sections of the device) to generate electricity through the use of hydraulic pistons and a generator capable of convert these pulses into electrical energy.

 

Systems of this kind, still in the research stage, are able to power small enough and for the first installation off the coast of Portuguese employing three devices evaluating a power of 2.25 MW.

Wave motion may also be exploited by means of a particular solution that provides for a particular wind turbine (Wells turbine) capable of rotating in the same direction regardless of the direction of flow.

In this solution there is provided a bell semi-submerged in the water, and in whose vertex is installed inside the turbine.

The wave rises or lowers cyclically the water column contained on one side of the bell, and consequently the air contained in it which drives the turbine.

This system has the advantage to be affected in a much lower corrosion phenomena typical of the articles immersed in sea water.

The power for this type of solution, in reference to the existing plants, is of the order of 0.3 - 0.5 MW.

Another device is represented by a real turbine installed underwater and no longer capable of exploiting the wave, but the currents.

Such solutions are in the process of experimentation and study, and different geometries are possible.

The problems compared to the same wind consist in the high corrosivity of the marine environment, combined with the difficulty of installation of the systems.

Unfortunately the poor diffusion of these solutions, coupled to the state almost more than experimental for most of them makes it very difficult to provide examples and data on the actual energy production and therefore on the real potential.

 

10/05/2010

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Translated via software

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Source:

Italian version of ReteIngegneri.it