Folley’s research, the New Scientist says, shows that nearshore waves 0.5 to 2 kilometres from the coast carry 80 to 90 per cent of the usable energy of waves further out. He calculates that offshore waves carry exploitable power at a density of around 18.5 kilowatts per metre-slice, compared with about 16.5 kilowatts for nearshore ones.
Standard figures have historically overestimated the utility of offshore waves for two reasons, Folley tells the New Scientist. They allowed severe storms to push up the average power figures, says Folley; however in reality wave power devices generate little power in such storms because they may have to switch into a self-preservation mode.
Previous figures also assumed that offshore waves have a prevailing direction, Folley goes on to say in the article, in the same way that nearshore waves tend to move towards the coast. However it is now understood that offshore waves come from a greater range of directions meaning that some harvesters in an offshore wave farm would be blocked by others. Nearshore farms could be strung out in lines to avoid that, says Folley.
Folley’s findings, which have been published in two peer-reviewed papers, are backed up in the New Scientist report by leading wave energy academic Professor Ian Bryden of University of Edinburgh who finds the figures “convincing”.
The findings are good news for wave energy developers such as Aquamarine Power, whose Oyster technology is designed specifically to harness the energy found in nearshore waves. The company has identified 8GW of exploitable nearshore energy in UK and Irish waters – enough energy to power around seven million homes.
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