Pentland Firth tidal power "could provide half Scotland's electricity".

Guardian: “The tidal streams, which surge through the firth at five metres per second, could bring large amounts of renewable energy in reach within a decade if enough government support is available, said the Oxford University engineer behind the new study.” “From Anglesey to the Severn estuary to Portland Bill, the UK has the greatest potential for generating predictable, clean energy from tidal channels. Turbines are already operating at Strangford Loch in Northern Ireland and prototypes are being tested in the Menai Straits off Anglesey.
But the Pentland firth is the greatest resource. “It is almost certainly the best site for tidal stream power in the world,” said Thomas Adcock, at Oxford University, who led the new work published in the journal Proceedings of the Royal Society A. The water flow is rapid there because the tide shifting from the Atlantic into the North Sea is forced through a narrow eight-mile channel. ….They calculated that underwater turbines strung across the entire width of the firth could generate a maximum 1.9GW of energy, averaged across the fortnightly tidal cycle. That is equivalent to 16.5 terawatt hours of electricity a year, almost half Scotland’s entire annual electricity consumption in 2011. As Scotland already produces 14.6Twh a year of renewable energy, a fully exploited Pentland would bring Scotland close to meeting its aim of 100% renewable electricity by 2020.
However, Adcock’s estimate of 1.9GW is far lower than the Scottish government’s published estimate of 14GW, making suggestions of huge exports of electricity seem unlikely.
….Adcock said it would take 10 years to develop tidal power in the firth to a scale that had a national impact.”