Research and analysis

18. Severn tidal power: Grid study non-technical summary

An assessment of the potential impact of a tidal generation project in the Severn Estuary on the transmission system.


Grid Study Non-Technical Summary

This file may not be suitable for users of assistive technology. Request an accessible format.

If you use assistive technology (such as a screen reader) and need a version of this document in a more accessible format, please email Please tell us what format you need. It will help us if you say what assistive technology you use.


The potential impact of a tidal generation project in the Severn Estuary on the transmission system was last assessed in any detail in the 1980’s. As part of the Severn Tidal Power Feasibility Study launched in 2008, an up to date study was required, and National Grid were commissioned by DECC in February 2009 to undertake the engineering studies.

Scope of the Grid Study

National Grid were asked to study a representative large Severn tidal generation scheme, and a representative smaller scheme. They were not asked to study every option as this would add to the cost, and as the results could only be used to provide an indication of the likely impact, it was felt that the results from the two representative schemes could be extrapolated to the other schemes with a sufficient level of information.

National Grid were asked to study the Cardiff-Weston barrage and the Shoots barrage. To better facilitate the extrapolation of the findings of this study for Shoots, across to the two land connected lagoons, a generation capacity figure of 1.36GW was selected for Shoots rather than the estimated capacity for the barrage generation of 1.05GW. The impact of the smaller Beachley option can also be assessed by studying 1.36GW. Studying the representative large and small options provided further efficiencies as these proposals have the best available technical data which National Grid require as an input to their studies.

Published 15 March 2010