Coventry University, Coventry, CV1 5FB, UK
Wind passing over the surface of water gradually passes some of its energy into the water to create waves. If the wind has a reasonable velocity and persists for a long time across a long stretch of water then the resulting waves will be large and powerful. This is why certain locations around the World enjoy healthy wave climates: for them the predominant winds have travelled across several thousand kilometres of ocean and in so doing have generated annual average wave power levels of around 50 kW per metre of crest length. Other sites do not have such high power densities but are still potentially valuable.
The World wave power resource is estimated at 2'000 GW, largely to be found in deep water locations. This is in depths of 40m or more.
A great deal of technical progress has been achieved over the last 25 years of wave power development. Many of the prototype schemes are shore mounted and incorporate an Oscillating Water Column driving a self rectifying air turbine. These schemes have few moving parts, and with judicious choice of the structural size and geometry, and the turbine, the overall performance can be impressive. The shoreline resource, although easier to exploit, has lower power density (typically around 20 kW/m) than the deep water.
Several new prototype
systems with ratings of about 1 MW are under construction. Some are shore
mounted Oscillating Water Columns, but other concepts are being tested which
could pave the way for the deployment of many floating devices in offshore
"wave farms". These will harvest large amounts of energy from the
deep water waves at costs of less than $0.1/kWh.
The author Les Duckers is Chair of Environmental Sciences at Coventry University in the UK. He has a background in physics and engineering and has worked on wave energy R&D since 1978. Although the Coventry Groups efforts were directed at offshore systems such as the Edinburgh Duck and Coventry Clam, Les has had a long term interest in world developments and has visited a number of teams.
There will be much more coming about Ocean Energy on future ISEO website pages, such as Tidal Power and OTEC (Ocean Thermal Energy Conversion).
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