The ‘Shoots Barrage’: An Indicative Energy Technology Assessment of a Tidal Power Scheme

Abstract

Several tidal power schemes have been proposed for the River Severn Estuary between the South West of England and Wales. An indicative technology assessment has been undertaken in order to evaluate the so-called 'Shoots Barrage' over its foreseen lifespan of 120 years in terms of its cradle-to-site, operation and maintenance requirements. It would be located just upriver of the Severn road crossings in the United Kingdom (UK), involve an estimated cost of £3.2 bn to construct, and could potentially generate around 2.7 TWh per year (or a little under 1% of UK electricity demand). This scheme is favoured by environmental groups, because to its more benign environmental impacts compared with the much larger, Cardiff-Weston scheme. The present analysis suggests that the proposed Shoots Barrage would yield relatively attractive 'figures of merit' in terms of its net energy and carbon emissions, although its financial performance is poorer than alternative power generators.

A technology assessment of the proposed Cardiff–Weston tidal barrage, UK

“…The overall results show that the Cardiff-Weston tidal barrage would emit 9·5-11·0 grams carbon dioxide equivalent (gCO 2 e)/kWh e . This contrasts with the value associated with the Shoots barrage scheme, which would emit about 6·7-8·7 gCO 2 e/kWh e (Hammond et al, 2014). Work sponsored under the auspices of the IPCC (Moomaw et al, 2011) indicates the carbon dioxide intensity of alternative power generators: coal (without carbon dioxide capture and storage (CCS))~1000 g carbon dioxide/kWh e ; combined cycle gas turbines (CCGTs; without CCS) -443 g carbon dioxide/kWh e ; nuclear -66 g carbon dioxide/kWh e ; solar PV -32 g carbon dioxide/kWh e ; and onshore wind -10 g carbon dioxide/kWh e .…”

“…Taking a construction period of 6 years, this equates to a total energy payback of 8·6 years. This is slightly shorter than that of the much smaller Shoots barrage (Hammond et al, 2014), but this difference is not significant over a lifespan of 120 years. By applying opportunity cost convention, the EPP for the Cardiff-Weston barrage was only 7·0 years, which indicates a strong case (in energy terms) for the implementation of such a scheme.…”

“…The largest contributors in terms of the energy requirements for the scheme (see Figure 5) were associated with cement (28%) and the hydroturbines (22%). This contrasts with the Shoots barrage (Hammond et al, 2014), for which 58% of the embodied energy was related to limestone rock, assumed to be quarried and then shipped from the Glensanda superquarry in Scotland.…”

“…Comparisons are also made with the much smaller Shoots barrage scheme (costing about £3·2 billion to construct and could generate around 2·75 TWh/year (or a little under 1% of UK electricity demand)) that would be located upriver of the Severn Road crossings (see again Figure 1), which is favoured by several environmental groups because of its more benign ecological and environmental impacts (Hammond et al, 2014).…”

“…Links to the shore and national grid would require 400 kV transmission lines. In contrast, the 4·1 km long Shoots barrage scheme would use 'Straflo', or rim generator, turbines operating solely through ebb generation (Elliott, 2012;Hammond et al, 2014), potentially generating some 2·75 TWh/year.…”