“A subsea cable – which would be 1,000km long and sunk to depths of 1,000 metres – could meet 1.5% of UK electricity demand … [from] the highly reliable potential energy in Iceland’s hydro dams.” (http://www.theguardian.com/world/2013/oct/27/iceland-seeks-uk-funding-cable-project)

Provided the cable can be constructed so as not to be susceptible to the marine equivalent of geese flying into it.