OT: Ramblings on Tidal Power (long)

Chris Hogg · 2016-09-16T10:02:33+00:00

I've been doing some calculations on tidal power. There are two locations of immediate interest ATM, Swansea Tidal Lagoon and the Pentland Firth Tidal Stream. The former envisages a horseshoe-shaped barrier built out from the shoreline at Swansea and enclosing a large body of water. As tides ebb and flow, turbines are driven by the flow of water out of and into the lagoon . The latter takes advantage of the very strong tidal streams in the Pentland Firth, between the north coast of Scotland and the Orkney Isles, using underwater turbines rather like wind turbines . The Swansea scheme has a much-publicised maximum capacity of 320MW. It also claims to be able to supply power for 14 hours a day, and to be able to supply 155,000 homes. But what does that boil down to? The fourteen hours a day is the sum of four 3.5 hour periods of generation, interspersed with 2.5 hour periods of no generation at slack water while the tides turn. So very On-Off-On-Off. The Grid operators will love that! Although Swansea doesn't give the average power over a year, it's easy enough to calculate from the house numbers: it works out at about 58MW*. With an installed capacity of 320MW, that gives a capacity factor of about 18%. The cost of Swansea is going to be about £1bn, so about £17 million per MW of output, compared to Hinkley Point C at £6.2 million per MW . It would take about fifty schemes the size of Swansea to match the output of Hinkley C, at a cost of about £50bn. The Swansea scheme wants a strike price of at least £168/MWh, index linked for 35 years, nearly double the £92.5 strike price for Hinkley Point C but for the same length of time page5. It's only merit is that it's going to last a very long time, 120 years they claim, and because it isn't actually going to produce very much electricity, it won't put up the average price to the consumer by very much! In the Pentland Firth, the complete Atlantis Resources/Meygen scheme proposes a total of 269 turbines, each of...