The funnel of water between the north-east tip of Scotland and the Orkney Islands contains some of the most powerful tidal energy in the world. The exploitable resource at the time of the fastest running tides may be as much 8 gigawatts. One source I have talked to suggests the figure could even be as high as 20 gigawatts. As I write this note, the National Grid’s website gives an estimate of the electricity use at this moment – about 55 gigawatts at peak-time on a winter evening. Be in no doubt, the Pentland Firth is the single most important source of renewable energy in the UK. The power concentrated in this narrow stretch of water could comfortably provide London’s electricity need. And it is entirely predictable to within a few percent every minute of every day. The tidal power will peak twice every 24 hours in a cycle that the Grid will be able to plan for decades in advance.