This is entry number 17 of a blog on the implementation of the Planning Act 2008. Click here for a link to the whole blog.

Last month the government reported on its consultation to harness tidal power from the River Severn. This is likely to be the first major project to tap into one of the last unexploited types of natural energy in and around the UK. Unlike wave and wind power, tidal power is predictable in terms of timing and scale. Today’s entry looks at the shortlisted schemes and examines whether they will have to seek approval under the Planning Act 2008 as Nationally Significant Infrastructure Projects (NSIPs).

Five schemes were shortlisted (the list was not made any shorter by the consultation). Three of them are barrages – i.e. they span the estuary – and two are lagoon projects – i.e. they impound water at one shore and let it in and out. The options are therefore not mutually exclusive.

The Beachley Barrage is the furthest upstream – it is upstream of the Wye near Chepstow. It is estimated to generate 2.7 terawatt hours per year (TWh/year).

The Shoots Barrage is next – it crosses the Severn near the road bridges from north of Avonmouth to south of Caldicot, and is estimated to generate 1.6TWh/year.

The final barrage is the Cardiff-Weston Barrage, whose name suggests its route. It is the most expensive and the furthest downstream, estimated to generate 16.8TWh/year or 5% of the UK’s electricity needs.

The upstream lagoon on the Welsh side is the Fleming Lagoon between Newport and the road bridges, estimated to generate 2.3TWh/year.

Finally, the downstream lagoon on the English side is the Bridgwater Bay Lagoon between Hinkley Point (another source of low-carbon electricity as it is the site of a nuclear power station) and Weston-super-Mare. It would generate 2.6TWh/year.

Would any of these be NSIPs? The two questions are whether the Act applies to generating stations in Wales or off Welsh waters, and whether these projects are above the size threshold as offshore ones of at least 100MW.

The answer to the first question is that the Act does apply to generating stations in Wales as well as England (although note that not all NSIP categories do apply in Wales), and also to Welsh as well as English waters.

For the answer to the second question, as is fairly often the case in assessing NSIPs, the project is given in different units and must be converted. In this case, one must convert terawatt hours per year to megawatts. A terawatt is a million megawatts (from the Greek for ‘monster’, rather than the Greek for just ‘big’) and there are about 8766 hours in a year, so one can calculate that 100MW is equivalent to 1.147TWh/year.

All five projects are therefore, not surprisingly, above the threshold and will have to use the new regime if they are applied for after 1 March 2010. As the next step is to look into the feasibility of each scheme, and applications are not expected to be made until 2014, this will certainly be the case for those that go ahead. So the answer to the question posed in the title is 'yes - and it may be more than one'.