Oceans and seas: recent boom of long-neglected energy sources

hydrokinetic, renewable marine energies, offshore wind turbines

On January 21st, French premier J-M Ayrault visited the STX shipyards in Saint-Nazaire and Montoir (Loire-Atlantique region) and laid the cornerstone of one of the two future Alstom plants where turbines will be manufactured and nacelles assembled. During his visit he announced that the government was working on a third call for tenders from the offshore wind power sector (following two tenders in April 2012 and January 2013) and that it was about to issue a call for projects to create a research programme on tidal and wave energy, thus demonstrating that renewable marine energies are at the heart of France’s industrial and energy policies.

Seas and oceans cover nearly 70% of the world’s surface and are bursting with energy flows, such as waves, currents and tides, which have been largely underexploited worldwide. And yet there is a range of techniques at hand to harness these resources. Although not all have yet reached technological and market maturity, two sectors have come to the fore which could achieve satisfactory industrial application by 2015.

Offshore wind power, pioneer in the renewable marine energy sector

Bottom-mounted offshore wind turbines apply the technology of conventional onshore wind power to the marine environment. It is therefore a reliable and mature technology which is increasingly widely used along the European coastline, with a generated power of over 5GW in the end of 2012. But the ocean is a remote and harsh environment where materials are subject to erosion by water and wind, hence the exploitation of offshore wind power in shallow near-shore waters.

The floating wind power industry designs ways to overcome such obstacles by adapting to the marine environment. By doing so, it involves new branches of industry, as many prototypes are being tested worldwide which encapsulate technologies uses in conventional wind turbines, petroleum engineering, offshore drilling and ship making. For instance, gravity-based single point anchor reservoirs (SPAR) or tension leg platform (TLP) derive directly from the offshore drilling industry.

Floating wind technology therefore makes it possible to harness energy from extremely potent air currents. It is a significant asset for countries like France which, contrary to countries bordering the North Sea, have no shallow offshore continental shelf below its territorial waters. As a practical example of how floating wind turbines address this issue, the Groix and Gulf of Fos test sites, both backed by the Institute of Excellence in marine renewable energy (France Energies Marine), are located in 60 to 70-metre-deep waters and are expected to achieve full-scale production between 2014 and 2016.

Other plans involve operating wind turbines moored in waters up to 200 metre deep, such as Statoil’s prototype Hywind off the coast of Norway since 2010. Although installation and maintenance of such equipment at such depths remain a challenge, it can be addressed by “recycling” offshore drilling platforms, moving floating elements to port facilities.

Hydrokinetic energy breakthrough to reach maturity

Technology generating energy from marine currents, also known as hydrokinetic energy, has been booming over the last few years and now appears promising. In 2011 this sector took a leap forward in France when the Open Hydro system was immersed thirty metre deep in a first ever attempted test under real conditions of a turbine with a sixteen-metre rotor diameter, in a partnership with DCNS. Another instance is the EDF marine energy plant (2 MW generation potential). Other projects include the Alstom ORCA project of an up to ten-metre-deep 1 MW turbine and the smalller Breton company Sabella. Such technology is actually being tested before it is industrially mature.

The advantages of hydrokinetic technology make it crucial to promote renewable marine energies. Potentials are high, although currently underexploited. France, for instance, is blessed with the second largest hydrokinetic energy sources in Europe behind the UK, that is an estimated 3 to 5 GW of potential installed power along its coasts in the medium run, which would represent a yearly production of 5 to 14 TW, depending on annual operating times. Besides, although the extent of energy derived from marine currents is variable, as in the case of most renewable energy sources, it is relatively predictable (tidal currents) and sometimes almost constant (deep water currents).

This sector has therefore some sort of competitive edge over wind power, from which it takes inspiration, all the more so as hydrokinetic turbines yield a greater power than a wind turbine of the same size, because water density is 800 times greater than the air’s.

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[1] French environment and energy management agency

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