NEAR-SHORE waves offer much better prospects for wave energy development than previously thought, according to a report published in the New Scientist. Indeed, author Dr Matt Folley, of Queen’s University, Belfast, who has calculated how much energy can be extracted from all wave types, has found that near-shore waves offer almost as much exploitable energy as offshore waves.
Folley’s research shows that near-shore waves 0.5-2km from the coast carry 80-90% of the usable energy of waves further out. He calculates that offshore waves carry exploitable power at a density of about 18.5 kilowatts per metre-slice, compared with about 16.5 kilowatts for near-shore ones. Standard figures have historically overestimated the utility of offshore waves. They allowed severe storms to push up the average power figures. However, Folley says that, in reality, wave-power devices generate little power in such storms because they may have to switch into a self-preservation mode (Pelamis is a prime example).
Previous figures also assumed that offshore waves have a prevailing direction in the same way that near-shore waves tend to move towards the coast.
Statisticians took to the seas in the 1970s. They used data from weather ships and buoys and calculated that the waves passing a one-metre wide slice of water at a 50m deep “offshore” location carried an average power of 40kW, double the power density of waves in 10m deep waters nearer the shore. Ever since, the wave-power industry has focused its attention 2-10km offshore in the belief that the greater energy yield would offset the higher price of maintenance and of relaying the power back to land.