ICE Dugald Clerk Lecture, London 29_01_2015

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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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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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


The Perfect Storm - Beddington

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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


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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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


Spring Tidal Energy Resource

Tidal Stream Tidal Range Source – DTI Atlas of Marine Renewable Energy Resources

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Wales

England

Bristol Channel & Severn Estuary


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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Tidal Energy Ltd

Tidal Stream Turbines


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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Red shows only economically viable sites- but cannot be sited in navigation channel

Potential Tidal Stream Sites


Designed by Prof Thorsten Stoesser - Cardiff University

Vertical Axis Turbine

Flow

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Same principles used as aircraft wing design:Lift force (horizontally) increases torque / efficiency

Lift Force

Blade Designed to Maximise Lift


CFD and Large Eddy Simulation

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Turbine Tested in Cardiff Slalom


Annapolis Royal Barrage – Nova Scotia1 x 20MW turbine and 2 sluices

Vertical Turbines Barrage Wakes

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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


DECC Schemes: Short List (2008)

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Source – Universityof Colorado

Output analysis often undertakenusing a simple 0-D analysis:-Reasonable small lagoons, Over-optimistic large lagoons

Tidal Lagoon Concept


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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Lagoon Proposals - Power Claims


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


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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Before stirring

Predicted to occur in Welsh Grounds Lagoon

After stirring

Note how sediment accumulates at centre of eddy

Tidal Eddies - Need to Minimise


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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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


First proposed by Thomas Fulljames - 1849

Barrage Across Severn - 1850

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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


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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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


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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STPG - Ebb-Only Generation


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


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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Dynamic region ofhigh turbidity

High Suspended Sediment Levels


Without Barrage With Barrage

Mean Flood - Spring Tide

Lower suspendedsediments clearer water

Suspended Sediment Levels

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But what type of birds?Dunlin or other birds?

Effects of Turbidity Changes?


Tidal reef design by Evans Engineering

Severn Embryonic Scheme

Tidal Reef - Low Head Scheme

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Without Barrage

Continental Shelf ModelBoundary Elevations

Reducedflood risk

Without Barrage

With Barrage

764 Bulb TurbinesNo Sluices

Two-Way Generation: Peak Levels


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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Wate

rL

eve

l(m

)

Po

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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

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10

12

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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


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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With Barrage

Without Barrage

With Barrage

216 Bulb Turbines166 Sluices (STPG)

Ebb-Only: Peak Currents



Without Barrage

With BarrageSimilar tonatural estuary

764 Bulb TurbinesNo Sluices

Two-Way: Peak Currents

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216 Turbines166 Sluices

Ebb-Only Generation (STPG)


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



With Barrage

Without Barrage

1026 VLH TurbinesNo Sluices

Peak Water Levels (2025)

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Without Barrage

Bund and Barrage

1026 VLH TurbinesNo Sluices

Sea level rise - 1.64m

Peak Water Levels (2145)


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


UK Relative Water Stress - EA

Low waterstress

High waterstress

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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

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Thank You

Professor Roger A. FalconerEmail: [email protected]

ICE Dugald Clerk Lecture, London 29_01_2015

Documents

Transcript of ICE Dugald Clerk Lecture, London 29_01_2015