'Extraordinary' operation to install water turbine off Orkney
The latest device to harness the power of the tides is being tested in the stormy waters off Orkney in the far north of Scotland.
The giant machine is like a wind turbine, but designed to withstand the massive forces of the currents.
Its developers, Scottish Power, plan to install 10 of the turbines off Islay next year in what would become the world's largest tidal array.
This comes amid growing interest from major engineering and power companies in the potential of tidal and wave energy.
BBC News Science Editor David Shukman went to see one of the turbines being put to the test.