Seite - 142 - in Water, Energy, and Environment - A Primer

8.7 OCEANENERGY Ocean energy comes in four distinct types (five if you include offshore wind energy): wave energy, ocean current energy, tidal energy, and OTEC (ocean thermal energy conversion). Together they represent a major new energy source for the world and all have been shown to work. The major problems are reliabilityandcost, andall are inearlystagesofdevelopment. 8.7.1 Waveenergy Wave energy is the most advanced of the ocean energy types, with several operating demonstration sites. Wikipedia defines ‘wave energy’ as ‘… the transport of energy by ocean surface waves, and the capture of that energy to do useful work – for example, electricity generation, water desalination, or the pumping of water (into reservoirs).’Wikipedia further explains that ‘Waves are generated by wind passing over the surface of the sea. As long as the waves propagate slower than the wind speed just above thewaves, there is an energy transfer from the wind to thewaves.’ 8.7.1.1 Waveenergyconversiondevices It is interesting to note that since wind energy is an indirect formof solar energy (winds are generated by uneven heating of the Earth’s surface by solar radiation), then so is wave energy. Waves are irregular, varying in frequency and height, and successful wave energy conversion (WEC) systems will tap as much as possible of the kinetic energy in the up and down motion of waves to generate electricity or mechanical power. R&D efforts, of which there are now many, with a major testing/demonstration site off the coast of Scotland, are focused on doing this energy capture at the lowest possible cost. Many different designs are being created and tested (see, e.g., Figure 8.18). Water,Energy, andEnvironment–APrimer142