Study considers Severn Barrage carbon payback
The proposed Severn Barrage would save so much carbon that the payback period for emissions released during construction would be less than six months.
Government is looking for ways to harness the huge tidal range of the river, with a large barrage being the biggest option currently on the table.
According to the CIWEM report, once the carbon cost is tallied for the production, transportation and construction of materials used for such a barrage it would still only take six months of operation to restore carbon neutrality - with huge carbon savings beyond that date.
The study says a 16km barrage would provide 5% of the UK's annual electricity demand, which is 25% of the UK target to cut emissions by 2020.
This is similar to that of all other renewable energy projects currently operating in the UK.
The authors of the report said: "The technical simplicity and reliability of tidal power schemes is dwarfed by the complexity of their political realisation, not least when environmental legislation is being tightened at a time of growing international concern about the security of energy supplies and, paradoxically, their predicted serious environmental effects.
"In time-honoured fashion, the decisions that have to be taken must be based on facts and rational debate. This paper adds an important dimension to that process."
Constructing the Severn Barrage would take about nine years but power generation could begin before the barrage is completed as long as it is 'closed' so it could begin its carbon payback when still incomplete and less than a year of operating at 85% annual output, it will have paid back the construction-related costs of the whole project.
Compared with its construction, the annual carbon cost of its operation is nominal. No energy intensive activities are involved as it should need little more than low-intensity maintenance during its expected 120 year lifespan.
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