that runs between the north coast of scotland and the oakney islands. it s an area well known for vicious winds and ripping tides. and that makes it the perfect location for developing new forms of clean energy. this narrow strip of water experiences tremendous title forces every single day, in fact they are some of the fastest tides in the world, and that means that there a tremendous reserve of energy if you can tap into it. and that s what s going on just over there, off the island of stroma. beneath the surface, are for gigantic turbines are four gigantic turbines which are generating electricity, right here. the power generated in the murky waters of the first by the power generated in the murky waters of the firth by these vast turbines is already being sold to the national grid. the past five years has been spent testing the technology, and the company behind them says it s ready for a major expansion. so fraser, tell me what we ve got here. we have a 150 tonne, 1.5 mw