1. North Wales Tidal Lagoon Jim Poole 2 October 2008

2. Concept T

3. Tidal Lagoon – Plan View
Dam wall
Outside
Inside
Water passing through turbines

4. Tidal Lagoon – Cross Section
Water at different level inside and outside lagoon
Dam Wall
Sea Bed

5. Operating Cycle - Simplified
Outside
Inside
Outside

6. Build up Head
Generate Electricity
Generate Electricity
Build up Head

7. Tidal Lagoon – Operation
Step 1: Build up head inside the lagoon by water level falling outside from high tide to low tide T

8. Tidal Lagoon – Operation
Step 2: Generate electricity by emptying lagoon from high tide level to low tide level T

9. Tidal Lagoon – Operation
Step 3: Build up head outside lagoon by water rising from low tide to high tide T

10. Tidal Lagoon – Operation
Step 4: Generate electricity by filling lagoon from low tide level to high tide level T

11. Proposed Location (Indicative)

12. Wind Farms (npower renewables)

13. For maximum generation
Water transfer takes place at high and low tide
The lagoon fills and empties completely over the full tidal range
Hence the mean head is equal to half the tidal range

14. Maximum generation over 2 tidal cycles
Potential Energy = 2  g A T2
= density of sea water
g = acceleration due to gravity
A = Area of lagoon
T = Tidal range
For proposed scheme (60km2),
maximum power = 343 MW

15. Practical Operation

16. Practical Operation
Only half the water is exchanged each time the lagoon empties or fills (rather than all of it)
The mean head is roughly 1/3 of the tidal range (rather than a half)
Hence electricity generated is only 1/3 of that potentially available

17. MAREC Paper – Headlines
Impoundment area: 60km2
Mean tidal range: 5.1m
Mean power output: 110MW
Construction cost: £285m - £540m
Net 3p/kWh: £25.9m/yr
Design life: 100yr (Turbines/Generators: 40yr)
(Mean power output of wind farm covering same area: 168MW)

18. Marec Paper – Reference
Evans, S., Poole, J.E.P. and Williams, K.P., “The North Wales Offshore Tidal Impoundment Scheme: a Preliminary Study of the Requirements, Constraints and Opportunities”, Third International Conference on Marine Renewable Energy, IMarEST, (Ed. C. French), Newcastle, July 2004, pp

19. A Model for Sustainability
The "Four-legged Table"
A Model for Sustainability
Quality
of Life
Env Ec
Soc
Nat Res

20. The "Four-legged Table"
Attacking the Gap

21. Context for North Wales Tidal Lagoon
The global picture
The local area
UK SD framework and energy policy

22. Global Context Climate change Rising sea level
Run-down in supplies of oil and gas
Increased use of renewable energy

23. Local Area - Environment
Shallow, gently-shelving coastal bay
Sea bed predominantly gravely sand
Mean spring tidal range: 6.7m
Mean neap tidal range: 3.5m
Coastal land below highest tide level
Sea wall in Towyn breached in 1990
One significant river – Afon Clwyd

24. Local Area – Towns Victorian seaside resorts “Faded glamour”
Rhyl contains one of the most deprived electoral wards in Wales
Now undergoing some redevelopment

25. Rhyl

27. Closed August 2007

28. April 2004

29. April 2004

30. April 2004

31. Towyn 1990

33. Towyn – strengthened defences

34. Cap’n Noahs
Meeting place for North Wales Coast Renewability Trust

35. Energy Review 2006 General Strategy: Save energy
Increase generation from renewables – from 4% to 20%
Strengthen EU Emissions Trading Scheme
Streamline planning system

36. Energy Review 2006 Tidal Impoundment Schemes:
Potential to make significant contribution to carbon reductions
But generally not competitive
Interested in improving understanding of tidal resource

37. UK SD Commission Turning the Tide: Tidal Power in the UK (Oct 2007):
“We therefore recommend that the Government investigates options to encourage one or more tidal lagoon demonstration projects. This could take the form of inclusion in the Renewables Obligation, or an open competition to solicit private sector or community interest. The additional expenditure would not need to be large, but the potential benefits could be extensive considering the resource available, both in the UK and internationally”.

38. Size and Positioning of Tidal Lagoon
Theory
Practice
Options

39. Theory (1) For a given shape: Construction costs = a L
Power generated = b L2
Where a, b are constants, L is the length of the impoundment wall
So:
Bigger is better

40. Theory (2) All other things being equal:
Rounder is better (more volume enclosed per unit length of impoundment wall)
Shallower is better (less “wasted” height below tidal range)

41. Practice Consider potential uses
Consider potential options for size and location
Assess options against uses

42. Potential Uses Power generation Coastal protection
Recreational boating
Marina facilities
Enhancing biodiversity (“atoll”)

43. Learn from elsewhere

44. Blyth – Power Generation

45. Blyth – Energy Research

46. Barry – Recreational Boating

47. Swansea Marina

48. Biodiversity

49. Size and Positioning Options
Offshore
Inshore
Onshore
Maximum power
Demonstration

50. Offshore
Minimum visual impact
River Clwyd

51. Better access from coast for recreational purposes
Inshore
Better access from coast for recreational purposes

52. Onshore
Response to rising sea levels
Doubles as a sea defence

53. Maximum Power
Follows contour lines

54. Part of a wider regeneration scheme
Demonstration
Part of a wider regeneration scheme

55. Demonstration - Details
Visitor Centre
Marina
Pier
Tramway

56. Demonstration Scheme

57. Marks out of Ten? Off In On Max Dem Power generation 5 7 10 2
Coastal protection 3 6
Recreational boating
Marina
Biodiversity

58. Nature of Construction Options
Traditional embankment dam
Geo-textile containers, filled with sand and gravel

59. Traditional Embankment Dam
Geo-membrane Layer
Rock Armour
Rubble Fill

60. Geo-textile Containers Filled with Sand and Gravel

61. Geo-textile Containers
ASR ltd. (New Zealand) & Soilfilters Australia pty. ltd.
TenCate Geosynthetics (Netherlands)

62. Links with Southern Hemisphere
ASR ltd. – New Zealand engineering consultancy, specialising in the design and construction of multi-purpose reefs
Soilfilters Australia pty. Ltd – manufacturer of geo-textile containers

63. Geo-textile Containers
Soilfilters Products:
“Terrafix” – a non-woven staple fibre geo-textile
“Softrock” – Terrafix containers filled with sand
Example – Narrowneck Reef, Australia

67. Web Links – ASR ltd. http://www.asrltd.co.nz/downloads.htm

68. TenCate Geosynthetics
Geocontainer (water depth > 3 metres)
Geotube (water depth < 3 metres)

72. Geotube

75. TenCate Geosynthetics Web Link

76. Geo-textile Containers Advantages
Efficient use of resources
Reduced transport costs
Rapid construction
Potentially reversible
Broader relevance to coastal management at time of rapid climate change

77. Different Methods of Operation
Tidal Lagoons
Different Methods of Operation
The aim is to extend the period of electricity generation over the tidal cycle

78. Calculation of Energy Converted
E = m g h
E = Energy converted (J)
m = Mass of water rising or falling (kg)
g = Acceleration due to gravity (m/sec2)
h = Height through which water rises or falls (m)

79. Calculation of Energy Converted
Taking:
Tidal range (T) = T m
Density of sea water = 1000 kg/m3
Acceleration due to gravity (g) = 10 m/sec2
The energy converted from tidal to electrical has been calculated for 1m2 of the lagoon

80. Fluctuation in sea level with the tides – a sine wave

81. Build up Head
Generate Electricity
Generate Electricity
Build up Head

82. Option 1: Lagoon fills and empties over full tidal range with transfer taking place at high and low tide.

83. Level of water inside impoundment

84. Net electricity generated per tidal cycle (Joules/metre2)
Mode of generation
Electricity generated
Option 1 (At high and low tide)
10,000T2
T = Tidal Range (m)

85. Problem with Option 1
A huge amount of electricity would be generated over short periods of time.
This would require high installed generating capacity and would not match the pattern of electricity demand.
The challenge is to extend the period of generation over the tidal cycle.

86. Option 2: Lagoon fills and empties over full tidal range, with transfer starting when the head reaches 0.25T.

87. Level of water inside impoundment

88. Net electricity generated per tidal cycle (Joules/metre2)
Mode of generation
Electricity generated
Option 1 (At high and low tide)
Option 2 (Starting with head of 0.25T)
10,000T2
4,360T2
T = Tidal Range (m)

89. Problem with Option 2
Rapid filling and emptying of lagoon required at either end of the tidal cycle.

90. Level of water inside impoundment

91. Problem with Option 2
Rapid filling and emptying of lagoon required at either end of the tidal cycle.
The solution is to speed up filling and emptying by active pumping.
This can result in a net increase in the electricity generated, since pumping takes place against a low head and generation with a higher head.

92. Level of water inside impoundment

93. Conditions for pump storage
For all tides the level inside the lagoon would be kept within the range currently observed for a natural spring tide.
The water level inside the lagoon is quarter of a cycle out of phase, when compared with the level outside.
This mode of operation termed “ECOSTAR”

94. ECOSTAR
Sustainable net Energy Capture Obtainable by Storage for Tidally Amplified Release.
Dr Stuart H Anderson, 2006.

95. Correction for calculating net electricity generation with pump storage
The energy for pumping has been multiplied by an arbitrary factor of 1.25 to reflect lower efficiency when compared with electricity generation.

96. Option 3: Lagoon fills and empties over full tidal range with active pumping to high and low tide level.
This option would be used for spring tides.

97. Level of water inside impoundment

98. Net electricity generated per tidal cycle (Joules/metre2)
Mode of generation
Electricity generated
Option 1 (At high and low tide)
Option 2 (Starting with head of 0.25T)
Option 3 (Pump storage within T)
10,000T2
4,360T2
6,930T2
T = Tidal Range (m)

99. Option 4: Lagoon fills and empties over full tidal range with active pumping to a level 0.17T higher than external high tide and 0.17T lower than external low tide level.
This option would be used for medium tides.

100. Level of water inside impoundment

101. Net electricity generated per tidal cycle (Joules/metre2)
Mode of generation
Electricity generated
Option 1 (At high and low tide)
Option 2 (Starting with head of 0.25T)
Option 3 (Pump storage within T)
Option 4 (Pump storage of +/- 0.17T)
10,000T2
4,360T2
6,930T2
9,020T2
T = Tidal Range (m)

102. Option 5: Lagoon fills and empties over full tidal range with active pumping to a level 0.5T higher than external high tide and 0.5T lower than external low tide level.
This option would be used for neap tides.

103. Level of water inside impoundment

104. Net electricity generated per tidal cycle (Joules/metre2)
Mode of generation
Electricity generated
Option 1 (At high and low tide)
Option 2 (Starting with head of 0.25T)
Option 3 (Pump storage within T)
Option 4 (Pump storage of +/- 0.17T)
Option 5 (Pump storage of +/- 0.5T)
10,000T2
4,360T2
6,930T2
9,020T2
12,660T2
T = Tidal Range (m)

105. Option 6: Lagoon fills and empties over the top half of the tidal range with generation on the ebb tide only.
This is the operating method currently proposed for the Severn Barrage.

106. Level of water inside impoundment

107. Net electricity generated per tidal cycle (Joules/metre2)
Mode of generation
Electricity generated
Option 1 (At high and low tide)
Option 2 (Starting with head of 0.25T)
Option 3 (Pump storage within T)
Option 4 (Pump storage of +/- 0.17T)
Option 5 (Pump storage of +/- 0.5T)
Option 6 (Generation on ebb tide only)
10,000T2
4,360T2
6,930T2
9,020T2
12,660T2
2,930T2
T = Tidal Range (m)

108. Mean power output over tidal cycle (MW/km2)
Mode of generation
Mean Power output
Option 1 (At high and low tide)
Option 2 (Starting with head of 0.25T)
Option 3 (Pump storage within T)
Option 4 (Pump storage of +/ T)
Option 5 (Pump storage of +/- 0.5T)
Option 6 (Generation on ebb tide only)
0.224T2
0.098T2
0.155T2
0.202T2
0.283T2
0.065T2
T = Tidal Range (m)

109. Worked Example: Electricity generated per tidal cycle (kJ/m2)
Mode of Operation
Tidal Range (m) 6 9 12
Option 3 (Pump storage within T)
250
560
1,000
Option 4 (Pump storage of 0.17T)
325
730
1,300
Option 5 (Pump storage of 0.5T)
455
1,025
1,820
Option 6 (Ebb only generation
105
235
420

110. Worked Example: Mean power output over tidal cycle (MW/km2)
Mode of Operation
Tidal Range (m) 6 9 12
Option 3 (Pump storage within T)
5.6
12.5
22.4
Option 4 (Pump storage of 0.17T)
7.3
16.4
29.1
Option 5 (Pump storage of 0.5T)
10.2
23.0
40.8
Option 6 (Ebb only generation
2.4
5.3
9.4

111. Benefits of ECOSTAR operation
High rate of energy capture.
More even energy output over lunar cycle.
Generation over a larger proportion of individual tidal cycle.
More flexible operation – potentially better match with energy demand.

112. ECOSTAR turbine specification
Generate with low head.
Generate in both directions.
Pump at similar rates and with similar efficiency.
Allow fish to pass without harm.

113. Pump Storage: Recommendations
Operate pump storage (Option 3) for all tides, but maintain level inside the impoundment within the overall tidal range occupied by the maximum springs under natural conditions
Empty and fill the impoundment at a flow rate equivalent to that operating during a normal maximum spring tide
By observing these rules, the overall environmental impact during pump storage will fall within the range occurring under natural conditions – albeit with the largest tides

114. Generation on ebb and flood tides – with active pumping
Spring Tide

115. Medium Tide

116. Neap Tide

117. Way Forward Two-way generation with active pumping.
Construct using local material in geotextile containers.
Consider multiple uses at design stage.
Consider siting onshore to double as a sea defence.
Rhyl ideal as a demonstration site.

118. Suggested Energy Strategy
Identify energy demands (amount, time, place)
Minimise energy demands
Identify energy supplies (amount, time, place)
Match supplies to demands

119. Suggested Energy Strategy
To reduce CO2 emissions by 75%:
Halve energy demands
Of the remaining demand meet half from renewable sources

120. Tidal Lagoons
Predictable energy supply:
Amount
Timing

121. Tidal Lagoons Even out supply to grid by:
Using different areas around the UK coast
Operating in conjunction with tidal stream turbines

122. Tidal Lagoons Reduce climate change: … through renewable energy
Combat climate change:
… through coastal protection

123. “Do Nothing” is not an option

124. Strategic Impact
Even with a mean output of 110MW, the North Wales Tidal Lagoon would:
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

125. Overall Reflections Think long term Recognise climate change
Coastal settlements in the front line
Maintain morale of citizens
National policies and local projects depend on each other

126. Sustainable Development Brundtland Definition: “Development which meets the needs of the present without compromising the ability of future generations to meet their own needs”

127. Sustainable Development Revised Definition: “Development which meets present needs while striving equally to allow for the needs of future generations” North Wales Coastal Renewability Trust 2005 Conwy County Council 2005

128. … Please Contact

129. Web Site