Harvesting wave energy

30-10-2019 | Posted by Joaquín Martí

Energía del oleaje

Mankind is becoming increasingly aware of the problems that the planet faces if we do not make responsible use of our resources, both from the viewpoint of their finite character and from that of the associated waste and emissions.

A key point is how we generate our electricity, which nowadays we require for practically any activity. In that sense, a particularly attractive option is that offered by renewable sources, which do not consume our limited resources and can be tapped with moderate emissions and disruption: hydroelectric energy, solar, wind, tides, currents, waves, etc.

As an example, the waves of the world’s oceans deploy a massive amount of energy. With water depths larger than half the wavelength, the wave energy flux increases with the square of the significant wave height and with the wave period. For a moderate swell, with 3 m waves passing with an 8 s period, the energy flux is 36 kW per metre of crest.

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It has been estimated that coastal waves could provide an average power of about 2.1 TW, approximately equal to half of the world’s total electricity demand. Considering also that 50% of the world’s population lives within 60 km of the sea, wave energy immediately emerges as a promising candidate energy supplier.

The devil is in the detail. The ocean is an aggressive environment for placing anything. The very forces that are being harnessed for energy generation threaten the systems, the moving parts are a nightmare, maintenance is a frequent and expensive requirement, corrosion, interference with navigation, impact on sea life, etc. are some of the numerous problems faced. And they all have their cost implications.

Many systems have been tried with different degrees of success. One that appears to beat many of the problems mentioned is currently being proposed by SBM Offshore. Their new generation of Wave Energy Converters (S3® WEC) essentially consists in a submerged, fibre-reinforced elastomeric tube, filled with water, that locally expands and contracts in response to the varying pressures associated with the passage of the waves

The tube is wrapped with rings of electroactive polymers and their strain energy variation is directly converted into electrical potential energy. Of course, the system is not totally immune to the complex demands exerted by wave action.

Principia has been supporting SBM Offshore in relation with the simulation of various structural configurations. Apart from the numerical analyses, physical tests of different kinds have already been conducted in laboratory environments and, all going well, a large-scale prototype is planned to be tested at sea in 2021.

Initiatives of this kind will no doubt help us along the road of trying to get the energy that we need, without triggering the dire consequences that this used to entail.

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