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Wind turbines have the inside track

One of the unknowns in this equation is the extent to which offshore wind turbines will take a share in the marine renewables market. They are attractive to operators and investors because of their proven technology and, in the case of fixed-base turbines at least, for their known capital and operational costs. They are on the march, and gaining momentum. For example, the U.K. Government has recently suggested that 25 GW of offshore wind power should be developed in U.K. waters, in addition to the 8 GW already in place or planned.

Until now, offshore wind turbines have been sited in shallow water areas on fixed pylons. However, there are now a number of proposals for floating bases for turbines, and the first, "Hywind," has recently been launched off the Norwegian coast by Statoil Hydro. We can expect many more floating turbines in the future when they will be deployed in deep water in direct competition with wave energy converters.

Small is beautiful but big is better

So where does wave energy stand in relation to the strong support that offshore wind energy enjoys from governments, industry and the utilities? A factor, whose significance is not always appreciated, is the extent to which offshore wind turbines are increasing in size, so that 5 MW installations are becoming the norm and larger sizes are already being produced. For offshore devices, the advantages of scale are obvious and it is difficult to see how wave energy devices with rated powers of 1 MW or less will be able to compete with the new generation of wind turbines. An operator or investor is unlikely to choose five or more small devices, whether wind- or wave-driven, when a single, large device could do the same job.

Looking at the wave energy devices that are currently produced or under development, there are only a few, such as the Wave Dragon and the OWEL Grampus, that can match the larger offshore wind turbines in terms of rated power. Many wave energy devices cannot be scaled up because of the physics of the methods they use for harnessing the wave energy. Clearly, these smaller devices may have niche markets, but it seems unlikely that they have the potential to compete with offshore wind for producing the many gigawatts of power required to meet government targets.

The demand for renewable power is huge and, to meet this, large-scale devices are a technical and economic necessity. This is well understood by manufacturers of offshore wind turbines, and developers of wave energy devices need to adopt a similar philosophy.

It takes two to tango

Having made that point, it has to be said that there are synergies to be exploited where both wave energy converters and wind turbines can co-exist in a particular sea area. For example, as Eric Stoutenburg of Stanford University has pointed out, in many sites, the wind and wave patterns are not closely correlated. Indeed, waves can be generated by weather systems a thousand miles away when local wind conditions are calm. The lack of correlation has clear benefits for a consistent power output from sites containing a mix of wind and wave devices. In addition, wind and wave devices could share power cables and even platforms.

In shallow water areas, tidal steams are often strong and there are many systems in place, or under development, for exploiting this source of power. On the other hand, wave energy in such areas is rapidly attenuated by friction from the sea bed. However, in deeper water on western coasts, there is a strong case for deploying a mix of wave energy devices and offshore wind turbines. Suitable wind turbines are available "off the shelf," but there is an urgent need for high-output wave energy devices that can partner these turbines. Candidate wave energy devices need further development, financed by private and public sources, if they are to play a timely part in meeting future demands for renewable power. Careful assessment of capabilities versus opportunities can be expected to lead to profitable investment.

Looking ahead

Crystal balls are notoriously unreliable instruments but, looking into mine, it appears likely that offshore wind will, in the future, provide a significant proportion of government targets for renewable power. The outlook for wave energy is less certain, but it is basically complementary to offshore wind, and it has a huge potential, provided technologies that can match the power of wind turbines are supported and developed into commercially attractive propositions.

It would be a pity if, due to lack of suitable wave energy devices, ocean power production was to be dominated by offshore wind, when a more efficient use of available sites and investments could be achieved by exploiting the synergies of a wind power and wave power mix.

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