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Sioned Evans Jim Poole Keith Williams
The North Wales offshore tidal impoundment scheme: a preliminary study of requirements, constraints & opportunities Sioned Evans Jim Poole Keith Williams
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Aim To help scope a formal assessment
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Contents Concept Generating capacity Size, shape & siting
Mechanical & electrical Construction, materials & costs Sustainability Comparison with wind farms Conclusions
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Notional location of the proposed impoundment
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Concept T
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Size considered Rectangle: 12 km x 5 km
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Maximum generation over 2 tidal cycles
PE = 2 g A T2 Maximum power = 343 MW
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Practical Operation
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Practical Operation Volume exchanged = 0.5 V Mean head = 0.35 T
Power = 120 MW
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Overall Efficiency If turbine-generator sets are 90% efficient:
Power = 108 MW Overall efficiency = 31.5%
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Size, Shape & Siting Economy of scale Distance from shore
Effect on tidal flows Coastal protection
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Three Options “Minimum environmental impact”
“Maximum power generation” “Climate change”
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Mechanical & Electrical
24 bulb turbines Installed capacity 340 MW Siting? Cable to shore
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Construction Traditional embankment dam
Embankment dam, but with geo-membrane bags Concrete caissons
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Typical cross section of embankment dam
40° 10m 14m Rock Armour Corefill Area = 374m2 Geomembrane layer Typical cross section of embankment dam 5m 1.5m Mean sea level – Permanently Submerged Use of geo-membrane bags in dam construction
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Sources of Material Sand & gravel: North of Liverpool Bay
Adjacent sea bed Slate waste? Gwynedd
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Costs (1) Index method Cost 1 = Size 1 Cost 2 Size 2 n
Cost estimate (based on Swansea scheme and n = 0.7) = £224 million
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Costs: First Principles (£m)
Category Min Max Civil works 211 412 Turbine generators 48 80 Labour 6 11 Others 20 40 Total 285 543
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Payback Assume: Mean generation = 110 MW Sale price = 3p/kWh
Operating cost = £3m/y Net income = £25.9m/y Payback = 11 – 21 years
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Sustainability Local & strategic impacts
Simultaneous social, economic & environmental progress
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Environmental: local Food & Environmental Protection Act 1985 Part II
Environmental Impact Assessment Positive & negative impacts
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Environmental: strategic
Save 1 million tonnes CO2 emissions annually (coal-fired) Contribute 1 TWhr/annum towards Welsh Assembly Government’s target of 4 TWhr/annum from renewables by 2010
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Compare with wind farm Turbines & turbine separation as for North Hoyle Installed capacity 480 MW Load factor 35% Mean power output 168 MW
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Conclusions Power output Size, shape & siting Construction method
Payback Sustainability Comparison with wind farm Modelling
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