Tidal Power in the UK Research Report 3 – Review of Severn Barrage Proposals

Abstract

Following an introduction to the importance of the Severn estuary, an overview is provided of the extensive studies carried out on the Severn estuary mainly over the last 25 years covering both single basin and two-basin barrage schemes. The studies have shown consistently that tidal power schemes requiring long lengths of embankment (two-basin schemes) result in significantly higher unit costs of energy than equivalent schemes where length of embankment is kept to a minimum. The study considers two schemes for more detailed analysis as follows: 

  • The Cardiff-Weston barrage, as developed and promoted by the Severn Tidal Power Group (STPG) and located between Cardiff, Wales and Weston-super-Mare, Somerset, South West England
  • The Shoots barrage (formerly the English Stones barrage) as presently proposed by Parsons Brinkerhoff (PB) and located just downstream of the second Severn crossing

 Studies using various models have shown ebb generation is the preferred mode of operation at the Shoots barrage sites and ebb generation with flood pumping optimises energy output at CardiffWeston providing about 3% more energy output than simple ebb generation. 

There are two large-scale tidal barrages in operation at present: 

  • The 240MW barrage on La Rance, near St. Malo on the Brittany coast
  • The 20MW Annapolis Royal tidal power plant on an inlet to the Bay of Fundy, Nova Scotia

 The Rance barrage was commissioned in 1966 after a six-year construction period. Following some initial issues with generator fixings which were repaired without great difficulty, the barrage has operated successfully for 40 years, confirming the reliability of well-designed marine concrete and the operation of the bulb turbines (favoured by STPG for Cardiff-Weston). Operation has also shown that one-way ebb generation is generally preferable to two-way ebb and flood flow generation (as shown by the UK studies). The much smaller Annapolis Royal scheme, commissioned in 1984, has provided operational experience of the more compact Straflo (straight flow) turbine design favoured by PB for the Shoots barrage. After commissioning, there were some problems with rotor seals. This was resolved and otherwise, high reliability has been reported.

Tidal Power in the UK Research Report 3 – Review of Severn Barrage Proposals is located in United Kingdom.