An indicative energy technology assessment of the Cardiff-Weston Tidal Barrage (UK)

What is it about?

Several tidal power schemes have been proposed for the Severn estuary between south-west England and Wales, UK. In this paper the so-called Cardiff–Weston barrage is evaluated using various sustainability appraisal techniques to determine its net energy output, carbon dioxide footprint and financial investment criteria, alongside various critical technical and environmental issues. The barrage would be located seaward of the Severn Road crossings, involve an estimated cost of £21 billion to construct and could potentially generate some 16·8 TWh/year – about 4·4% of the UK electricity demand. An indicative energy technology assessment is undertaken to evaluate this tidal power scheme over its foreseen lifespan of 120 years in terms of its ‘cradle-to-site’, operation and maintenance requirements. The present analysis suggests that the proposed Cardiff–Weston barrage would yield relatively attractive ‘figures of merit’ in terms of its net energy and carbon dioxide emissions, although its financial performance is poorer than that of alternative power generators. Comparisons are also made with the much smaller Shoots barrage scheme proposed upstream of the Severn Road crossings, which is favoured by environmental groups due to its more benign ecological and environmental impacts.

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Why is it important?

Tidal power barrages give rise to unwanted side effects resulting in potential environmental hazards at local, regional and global scales. In a climate-constrained world, the primary concern on the global scale is anthropogenic climate change, due to an enhanced greenhouse effect induced by combustion-generated pollutants. The proposed Cardiff-Weston tidal barrage was found to have a carbon footprint of about 9·5–11·0 gCO2e/kWh. In both the energy and carbon dioxide analyses, the operational requirements and emissions of this barrage were found to have the most significant influence on the final results (accounting for around two-thirds of the emissions). It was not possible to include all the energy requirements associated with the scheme or the sources of carbon dioxide emissions from the project, such as those emanating from the manufacturing of the hydro-turbines and caissons. However, they are unlikely to have a significant impact on the energy and emissions indicators estimated here. Comparison has been made with the work sponsored by the IPCC that indicates the carbon dioxide intensity of alternative power generators. This suggests that both the Cardiff–Weston and smaller Shoots tidal power schemes display attractive figures of merit in terms of their carbon dioxide footprints, comparable with that of onshore wind over their respective life cycles. But, like other energy options, the Cardiff–Weston barrage gives rise to other ecological and environmental disbenefits at a more local scale. It will lead to significant modifications to the estuarine environment of the River Severn, resulting in the loss of inter-tidal habitat with potentially adverse effects on local plant and animal populations, in particular birds who feed on the tidal mudflats. However, many researchers acknowledge that much more information is needed on the impact of the Cardiff–Weston barrage on large-scale sediment circulation, the erosion of foreshores, biodiversity and water quality. Inevitably, the smaller Shoots tidal barrage is likely to have less severe ecological and environmental impacts than the larger Cardiff–Weston scheme.

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