1. 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

2. Aim
To help scope a formal
assessment

3. Contents Concept Generating capacity Size, shape & siting
Mechanical & electrical
Construction, materials & costs
Sustainability
Comparison with wind farms
Conclusions

4. Notional location of the proposed impoundment

5. Concept T

6. Size considered
Rectangle: 12 km x 5 km

7. Maximum generation over 2 tidal cycles
PE = 2  g A T2
Maximum power = 343 MW

8. Practical Operation

9. Practical Operation Volume exchanged = 0.5 V Mean head = 0.35 T
Power = 120 MW

10. Overall Efficiency If turbine-generator sets are 90% efficient:
Power = 108 MW
Overall efficiency = 31.5%

14. Size, Shape & Siting Economy of scale Distance from shore
Effect on tidal flows
Coastal protection

15. Three Options “Minimum environmental impact”
“Maximum power generation”
“Climate change”

16. Mechanical & Electrical
24 bulb turbines
Installed capacity 340 MW
Siting?
Cable to shore

17. Construction Traditional embankment dam
Embankment dam, but with geo-membrane bags
Concrete caissons

18. 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

19. Sources of Material Sand & gravel: North of Liverpool Bay
Adjacent sea bed
Slate waste?
Gwynedd

20. 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

21. Costs: First Principles (£m)
Category
Min
Max
Civil works
211
412
Turbine generators 48 80
Labour 6 11
Others 20 40
Total
285
543

22. Payback Assume: Mean generation = 110 MW Sale price = 3p/kWh
Operating cost = £3m/y
Net income = £25.9m/y
Payback = 11 – 21 years

23. Sustainability Local & strategic impacts
Simultaneous social, economic & environmental progress

25. Environmental: local Food & Environmental Protection Act 1985 Part II
Environmental Impact Assessment
Positive & negative impacts

27. 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

37. Compare with wind farm
Turbines & turbine separation as for North Hoyle
Installed capacity 480 MW
Load factor 35%
Mean power output 168 MW

38. Conclusions Power output Size, shape & siting Construction method
Payback
Sustainability
Comparison with wind farm
Modelling