Post on 11-Aug-2015
transcript
03/02/2015
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Institution of Civil EngineersDugald Clerk Lecture 2015
Dugald Clerk Lecture:
Tidal Energy - Challenges and Opportunities
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Institution of Civil EngineersDugald Clerk Lecture 2015
Professor Roger A. FalconerFREng, FICE
CH2M HILL Professor of Water Management
President - International Association for Hydro-Environment Engineering and Research
Hydro-environmental Research CentreSchool of Engineering, Cardiff University
Tidal Energy Resources:Challenges and Opportunities
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Institution of Civil EngineersDugald Clerk Lecture 2015
Some Key Considerations
Growing worldwide increase in energy demand
Climate change and population growth (globally and UK) leading to increase in energy demand
Decarbonising energy - rise in electricity demand
EU targets:- e.g. 20% from renewables by 2020
Tidal energy has advantage of being predictable
Severn Estuary basin is ideal site for tidal energy
Institution of Civil EngineersDugald Clerk Lecture 2015
The Perfect Storm - Beddington
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Institution of Civil EngineersDugald Clerk Lecture 2015
Existing Tidal Schemes: La RanceKey details:
Completed in 1966
24 x 5.3m dia. bulb turbines & 6 sluices
Turbine trials ebb-only (+ pumping)
Generate 0.54TWh/y
Now costs €20/MWh
No baseline studies prior to construction
Institution of Civil EngineersDugald Clerk Lecture 2015
Existing Schemes: Sihwa LakeKey details:
Completed in 2011
10 x 7.2m dia. bulb turbines & 6 sluices
Capacity = 254MW
Turbines operate onflood-only + sluicing
Need to balance mix of complex lake uses
Cost $250M + Lake
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Institution of Civil EngineersDugald Clerk Lecture 2015
Existing Schemes: MCT TurbinesKey details:
Tidal stream turbines
Typically 0.75-1.5MW
Monopile of dia. = 3m
Rotate at 10-20 RPM
Tested favourably in Strangford Lough
Deployment plans as multi-unit arrays
Institution of Civil EngineersDugald Clerk Lecture 2015
Spring Tidal Energy Resource
Tidal Stream Tidal Range Source – DTI Atlas of Marine Renewable Energy Resources
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Institution of Civil EngineersDugald Clerk Lecture 2015
Wales
England
Bristol Channel & Severn Estuary
Institution of Civil EngineersDugald Clerk Lecture 2015
2Power A HH = level difference across barrage/lagoon
A = wetted area impounded by barrage/lagoon:-Severn Barrage: A = 500km2 Lake Geneva
For tidal barrages and lagoons (Potential Energy):
V = mean free-stream tidal current
For tidal stream turbines (Kinetic Energy):
Power 3
Potential Power from Tides
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Institution of Civil EngineersDugald Clerk Lecture 2015
Tidal Energy Ltd
Tidal Stream Turbines
Institution of Civil EngineersDugald Clerk Lecture 2015
Key details:
Rotor diameter = 15m (x3)
Minimum depth = 25m below LAT
Installed capacity = 1.2MW
Capital cost = £3million/MW
Tested / installed - Ramsey Sound
Tidal Stream Turbines
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Institution of Civil EngineersDugald Clerk Lecture 2015
Red shows only economically viable sites- but cannot be sited in navigation channel
Potential Tidal Stream Sites
Institution of Civil EngineersDugald Clerk Lecture 2015
Designed by Prof Thorsten Stoesser - Cardiff University
Vertical Axis Turbine
Flow
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Institution of Civil EngineersDugald Clerk Lecture 2015
Same principles used as aircraft wing design:Lift force (horizontally) increases torque / efficiency
Lift Force
Blade Designed to Maximise Lift
Institution of Civil EngineersDugald Clerk Lecture 2015
CFD and Large Eddy Simulation
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Institution of Civil EngineersDugald Clerk Lecture 2015
Turbine Tested in Cardiff Slalom
Institution of Civil EngineersDugald Clerk Lecture 2015
Annapolis Royal Barrage – Nova Scotia1 x 20MW turbine and 2 sluices
Vertical Turbines Barrage Wakes
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Institution of Civil EngineersDugald Clerk Lecture 2015
Key details:
Wall 9.7km
16 bulb turbines
Area 11.6km2 5.8 x Cardiff Bay
Novel design for embankment
Reported energy output 0.4TWh/y
Pilot for studying lagoon potential
Swansea Bay Lagoon at Planning
Institution of Civil EngineersDugald Clerk Lecture 2015
DECC Schemes: Short List (2008)
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Institution of Civil EngineersDugald Clerk Lecture 2015
Source – Universityof Colorado
Output analysis often undertakenusing a simple 0-D analysis:-Reasonable small lagoons, Over-optimistic large lagoons
Tidal Lagoon Concept
Institution of Civil EngineersDugald Clerk Lecture 2015
Classic paper on 0-D analysis widely used: Prandle, D., Advances in Water Resources, 1984, 7, 21-27
Key assumptions in paper need care, including:
‘Water level within basin is horizontal’ not valid for large lagoons
‘Surface area of basin is constant’ i.e. Area f(t) invalid for many lagoon proposals (e.g. Severn)
‘During power generation flow through turbines is at a constant rate’ unlikely for large lagoons
‘Simple Theory --- Tidal Analysis’
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Institution of Civil EngineersDugald Clerk Lecture 2015
Lagoon Proposals - Power Claims
Institution of Civil EngineersDugald Clerk Lecture 2015
Included in DECC studies, Area 80km2
Installed Capacity = 1,360MW
Welsh Grounds Lagoon
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25 Sluices
60 Turbines 25 Sluices
Welsh Grounds
Newpor
t Dee
p Avonmouth
Newport
Welsh Grounds Grid Configuration
Institution of Civil EngineersDugald Clerk Lecture 2015
2 2.5 3 3.5 4 4.5 5 5.5 6
2 m/s
Water level (m)
Flood0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
2 m/s
Water level (m)
Ebb
(a) During Filling Mode (b) During Emptying Mode
Peak Power Output: (i) 0-D analysis 1,300MW(ii) 2-D model analysis 900MW & strong eddies
Notice strongeddies
Notice lowerebb current
Velocity Field Around Turbines
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Institution of Civil EngineersDugald Clerk Lecture 2015
Before stirring
Predicted to occur in Welsh Grounds Lagoon
After stirring
Note how sediment accumulates at centre of eddy
Tidal Eddies - Need to Minimise
Institution of Civil EngineersDugald Clerk Lecture 2015
P1C1
P2C2
Dynamic Pressure Force P1 = P2Bottom Friction V2 < V1Centrifugal Force C2 < C1So:- Particle Moves Towards Centre
Dynamics of Particle in an Eddy
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Institution of Civil EngineersDugald Clerk Lecture 2015
Incoming Tide
Impoundment
Depositionremains
Outgoing Tide
Area of deposition
Jet Flow
Flow to Sink
Predicted to occur in Welsh Grounds Lagoon
Tidal Pumping - Need to Avoid
Institution of Civil EngineersDugald Clerk Lecture 2015
First proposed by Thomas Fulljames - 1849
Barrage Across Severn - 1850
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Institution of Civil EngineersDugald Clerk Lecture 2015
Tide Range - 14 m on springs, 7 m on neaps
High tidal currents and large inter-tidal areas
30 Mt sediment suspended on springs, 4 Mt neaps
Little sunlight penetration through water column
Reduced saturation dissolved oxygen levels
Ecology
Harsh estuarine regime with high currents
Limited aquatic life in water column and over bed
Bird numbers per km2 relatively small - but unique
Unique Estuarine Environment
Institution of Civil EngineersDugald Clerk Lecture 2015
Climate Change
Temperature rise will affect ecology, birds etc.
Sea level rise will lead to increased flood risk
Water Quality
Cleaner effluent discharges with EU WFD
Nutrient reduction will affect aquatic life
Legislation
Long term projects (>120 yr) require assessment against future environment - as well as current
Changing Estuarine Environment
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Institution of Civil EngineersDugald Clerk Lecture 2015
Key details:
2nd highest spring tidal range 14 m
Cardiff to Weston
Length about 16 km
Generate 5% of U.K. electricity
Total cost £20 bn
Save > 6.8 million tonnes carbon pa
Slides courtesy of STPG - David Kerr
Severn Tidal Power Group Scheme
Institution of Civil EngineersDugald Clerk Lecture 2015
Key details:
216 turbines each 40 MW 17 TWh/yr
166 sluices
Ship locks
Fish pass?
Public road and rail?
STPG Scheme - DECC Short List
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Institution of Civil EngineersDugald Clerk Lecture 2015
STPG - Ebb-Only Generation
Institution of Civil EngineersDugald Clerk Lecture 2015
Inner Barrage
Cardiff
Severn Estuary Computer Model
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2 m/s
water level(m)
-4 -3 -2 -1 0 1 2 3
2 m/s
water level(m)
2 2.5 3 3.5 4
Flood
Ebb
Velocity Field for STPG Barrage
Institution of Civil EngineersDugald Clerk Lecture 2015
Spring tide range reduced from 14 m to 7 m Large loss of upstream inter-tidal habitats ( 140km2)
Reduced currents up/downstream of barrage ( 50%)
Reduced turbidity and suspended sediment levels
Increased light penetration through water column with increased water clarity
Increased primary productivity and changed bio-diversity of benthic fauna and flora
Upstream tidal range of 7m still relatively large compared to most estuaries world-wide
Main Impacts of STPG Barrage
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Institution of Civil EngineersDugald Clerk Lecture 2015
Dynamic region ofhigh turbidity
High Suspended Sediment Levels
Institution of Civil EngineersDugald Clerk Lecture 2015
Without Barrage With Barrage
Mean Flood - Spring Tide
Lower suspendedsediments clearer water
Suspended Sediment Levels
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Institution of Civil EngineersDugald Clerk Lecture 2015
But what type of birds?Dunlin or other birds?
Effects of Turbidity Changes?
Institution of Civil EngineersDugald Clerk Lecture 2015
Tidal reef design by Evans Engineering
Severn Embryonic Scheme
Tidal Reef - Low Head Scheme
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Institution of Civil EngineersDugald Clerk Lecture 2015
Without Barrage
Continental Shelf ModelBoundary Elevations
Reducedflood risk
Without Barrage
With Barrage
764 Bulb TurbinesNo Sluices
Two-Way Generation: Peak Levels
Institution of Civil EngineersDugald Clerk Lecture 2015
Ebb-only scheme shows marked rise in groundwater levels
Mean groundwater raised by 2m
Two-way scheme shows little change in groundwater levels
Mean groundwater level unchanged
Changes to Water Elevations
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Institution of Civil EngineersDugald Clerk Lecture 2015
Wate
rL
eve
l(m
)
Po
we
ro
utp
ut(G
W)
0 2 4 6 8 10 12 14 16 18 20 22 24-10
-9-8-7-6-5-4-3-2-10123456
0
2
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Time (hour)
Water level (m)Upstream of the barrage
Water level (m)Downstream of the barrage
Power Generation Power Generation24.4 Gwh 24.4 Gwh
I II III II
I=Filling (4.3h)
II=Holding (1.6h+1.0h)
III=Generating (5.5h)
4m
2m
(a)(a)
Wa
ter
Le
vel(
m)
Po
we
ro
utp
ut
(GW
)0 2 4 6 8 10 12 14 16 18 20 22 24
-10-9-8-7-6-5-4-3-2-10123456
0
2
4
6
8
10
12
14
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Time (hour)
Water level (m)Upstream of the barrage
Water level (m)Downstream of the barrage
PowerGeneration
PowerGeneration
8.3 Gwh 8.3 Gwh15.9 Gwh 15.9 Gwh
I II
Releasing (0.8h+1.1h)
II=Holding (2.0h+1.3h)
III=Generating (2.8h+4.4h)
4m
2m
III III (d)
I=Filling and
(c)
Ebb Only
48.8 GWh/24.8h
5.2 m mean tide
High tide 4.6 m
Power for 11h
Two‐Way
48.4 GWh/24.8h
4.4 m mean tide
High tide 3.2 m
Power for 15h
Water Levels and Power Output
Institution of Civil EngineersDugald Clerk Lecture 2015
Potential energy output of 26TWh/yr - 4h out of phase with Severn
Lagoons: N Wales & NW England
Need to be designed tominimise circulation
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Institution of Civil EngineersDugald Clerk Lecture 2015
Continental Shelf ModelBoundary Elevations
With Barrage
Without Barrage
With Barrage
216 Bulb Turbines166 Sluices (STPG)
Ebb-Only: Peak Currents
Institution of Civil EngineersDugald Clerk Lecture 2015
Continental Shelf ModelBoundary Elevations
Without Barrage
With BarrageSimilar tonatural estuary
764 Bulb TurbinesNo Sluices
Two-Way: Peak Currents
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Institution of Civil EngineersDugald Clerk Lecture 2015
216 Turbines166 Sluices
Ebb-Only Generation (STPG)
Institution of Civil EngineersDugald Clerk Lecture 2015
764 TurbinesNo Sluices
Two-Way Generation
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Key details:
1026 VLH turbines 16.4TWh/yr
No sluice gates
Length 18km
Total cost £25bn
Ship locks
Save > 7.2 million tonnes carbon pa
Road and/or rail?
Hafren Power Scheme Proposal
Institution of Civil EngineersDugald Clerk Lecture 2015
Continental Shelf ModelBoundary Elevations
With Barrage
Without Barrage
1026 VLH TurbinesNo Sluices
Peak Water Levels (2025)
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Institution of Civil EngineersDugald Clerk Lecture 2015
Continental Shelf ModelBoundary Elevations
Without Barrage
Bund and Barrage
1026 VLH TurbinesNo Sluices
Sea level rise - 1.64m
Peak Water Levels (2145)
Institution of Civil EngineersDugald Clerk Lecture 2015
Scheme Power (GW) Energy (TWh/yr) Base Cost (£bn)
Tidal Stream TEL 100 x Turbines
0.12 0.28 0.36
Tidal Reef 5 20 21.2 (Atkins)
Cardiff‐Weston DECC (STGP)
8.6 15.6 23.2
Bridgwater Bay Lagoon
3.6 6.2 12.0
Welsh Grounds Lagoon
1.3 3.0 7.0
Swansea Bay Lagoon(Source: BBC 02/14)
0.25 0.4 0.85
Table adapted from DECC study
Severn Region Options
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Levelised Cost Comparison
Hafren Power, http://www.hafrenpower.com/severn‐barrage/cost.html
Institution of Civil EngineersDugald Clerk Lecture 2015
UK Relative Water Stress - EA
Low waterstress
High waterstress
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Institution of Civil EngineersDugald Clerk Lecture 2015
Tidal stream turbines Limited to site around Minehead -
Aberthaw; Vertical axis turbines in barrage wake?
Tidal lagoons Expensive at large scale; Require accurate modelling; Flow complex; Design critical; Any lagoons in Severn Estuary jeopardise barrage efficiency
Severn Barrage Two-way generation would: Produce 5% UK electricity; Maintain estuary flow features; Reduce far field impact; Much reduce inter-tidal habitat loss; Major flood risk reduction upstream; Pumping and sluicing could address Port concerns and fish migration; Much scope for strategic development of region (SW England & SE Wales)
Summarising