Tapping into Severn tides

Tuesday November 10th: It’s beginning to sink in that we really do have to find ways to generate electricity that don’t depend on fossil fuels, and one obvious possibility is to tap into the tidal power of the Severn Estuary, which has the third largest tidal range (rise and fall) in the world. The government is running a feasibility study, and BRLSI’s Transport and Built Environment Group managed to get James Colcome, Project Manager of the study, to come to Bath to give a presentation on the five short-listed options.
First Mr Colcombe gave some background details on tidal power, including the fact that there are two distinct types – range (which the Severn has) and stream (speed and volume of water flow), at which the Pentland Firth in Scotland is UK champion. Range systems depend on ‘differential head’ (height of water) across the generating turbines (basically the same as a hydro-electric dam system), and there are three ways of implementing them, with varying effects on generating times in relation to tides and water levels upstream of the barrage – and on silting and other environmental impacts.
Of the five contenders for the Severn, only three are barrages that cross the entire waterway; two (seen in the picture above) are lagoons along the side of the estuary, which don’t affect the upstream river, but generate less electricity. Although
Mr Colcombe was scrupulously even-handed in his comments, it looks as if the current front-runner is the Cardiff to Weston-super-Mare (actually Lavernock to Brean) barrage, whose 216 turbines would generate the most electricity (14% of our renewables target) at the lowest unit cost.
It’s not a done deal yet though, and a long list of potential issues, from wildlife habitats to salinity affecting ship buoyancy, showed that the decision is unlikely to be a quick one. And one statistic showed that other considerations may yet apply – in a table of costs per Megawatt/hour of electricity, nuclear power came in at £38, against the cheapest tidal figure of £110. There’s certainly more discussion to come.