Dugald Clerk Lecture: Tidal Energy - Challenges and Opportunities

Transcription

1 Monday 2 February 2014 Dugald Clerk Lecture: Tidal Energy - Challenges and Opportunities

2 Marine Energy Resources: Challenges and Opportunities Professor Roger A. Falconer FREng, FICE CH2M HILL Professor of Water Management President - International Association for Hydro- Environment Engineering and Research Hydro-environmental Research Centre School of Engineering, Cardiff University

3 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

4 The Perfect Storm - Beddington

5 Existing Tidal Schemes: La Rance Key details: Completed in x 5.3m dia. bulb turbines & 6 sluices Turbine trials ebbonly (+ pumping) Generate 0.54TWh/y Now costs 20/MWh No baseline studies prior to construction

6 Existing Schemes: Sihwa Lake Key details: Completed in x 7.2m dia. bulb turbines & 6 sluices Capacity = 254MW Turbines operate on flood-only + sluicing Need to balance mix of complex lake uses Cost $250M + Lake

7 Existing Schemes: MCT Turbines Key details: Tidal stream turbines Typically MW Monopile of dia. = 3m Rotate at RPM Tested favourably in Strangford Lough Deployment plans as multi-unit arrays

8 Spring Tidal Energy Resource Tidal Stream Tidal Range Source DTI Atlas of Marine Renewable Energy Resources

9 Wales Bristol Channel & Severn Estuary England

10 Potential Power from Tides For tidal stream turbines (Kinetic Energy): Power V 3 V = mean free-stream tidal current For tidal barrages and lagoons (Potential Energy): Power A H 2 H = level difference across barrage/lagoon A = wetted area impounded by barrage/lagoon:- Severn Barrage: A = 500km 2 Lake Geneva

11 Tidal Stream Turbines Tidal Energy Ltd

12 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

13 Potential Tidal Stream Sites Red shows only economically viable sites - but cannot be sited in navigation channel

14 Vertical Axis Turbine Flow Designed by Prof Thorsten Stoesser - Cardiff University

15 Blade Designed to Maximise Lift Lift Force Same principles used as aircraft wing design: Lift force (horizontally) increases torque / efficiency

16 CFD and Large Eddy Simulations

17 Turbine Tested in Cardiff Slalom

18 Turbine Tested in Cardiff Slalom

19 Vertical Turbines Barrage Wakes Annapolis Royal Barrage Nova Scotia 1 x 20MW turbine and 2 sluices

20 Swansea Bay Lagoon at Planning Key details: Wall 9.7km 16 bulb turbines Area 11.6km x Cardiff Bay Novel design for embankment Reported energy output 0.4TWh/y Pilot for studying lagoon potential

21 DECC Schemes: Short List (2008)

22 Tidal Lagoon Concept Output analysis often undertaken using a simple 0-D analysis:- Reasonable small lagoons, Over-optimistic large lagoons Source University of Colorado

23 Simple Theory --- Tidal Analysis Classic paper on 0-D analysis widely used: Prandle, D., Advances in Water Resources, 1984, 7, 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

24 Lagoon Proposals - Power Claims

25 Welsh Grounds Lagoon Included in DECC studies, Area 80km 2 Installed Capacity = 1,360MW

26 Welsh Grounds Grid Configuration Frame Sep 2008 Initial bathymetry Newport Welsh Grounds 25 Sluices 60 Turbines 25 Sluices Newport Deep Avonmouth

27 Velocity Field Around Turbines ame Sep 2008 Hydrodynamic Results in Nodes Flood Water level (m) m/s Frame Sep 2008 Hydrodynamic Results in Nodes Ebb Water level (m) m/s Notice strong eddies (a) During Filling Mode Notice lower ebb current (b) During Emptying Mode Peak Power Output: (i) 0-D analysis 1,300MW (ii) 2-D model analysis 900MW & strong eddies

28 Tidal Eddies - Need to Minimise Note how sediment accumulates at centre of eddy Before stirring After stirring Predicted to occur in Welsh Grounds Lagoon

29 Dynamics of Particle in an Eddy C1 P1 C2 P2 Dynamic Pressure Force P1 = P2 Bottom Friction V2 < V1 Centrifugal Force C2 < C1 So:- Particle Moves Towards Centre

30 Tidal Pumping - Need to Avoid Jet Flow Area of deposition Flow to Sink Deposition remains Impoundment Incoming Tide Outgoing Tide Predicted to occur in Welsh Grounds Lagoon

31 Barrage Across Severn First proposed by Thomas Fulljames

32 Unique Estuarine Environment 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 km 2 relatively small - but unique

33 Changing 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

34 Severn Tidal Power Group Scheme 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 Slides courtesy of STPG - David Kerr Save > 6.8 million tonnes carbon pa

35 STPG Scheme - DECC layout Key details: 216 turbines each 40 MW 17 TWh/yr 166 sluices Ship locks Fish pass? Public road and rail?

36 STPG - Ebb-Only Generation

37 Severn Estuary Computer Model Cardiff Inner Barrage

38 Velocity Field for STPG Barrage Flood Frame Apr 2008 Hydrodynamic Results in Nodes 2 m/s water level(m) Ebb 2 m/s water level(m)

39 Main Impacts of STPG Barrage Spring tide range reduced from 14 m to 7 m Large loss of upstream inter-tidal habitats ( 140km 2 ) 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 biodiversity of benthic fauna and flora Upstream tidal range of 7m still relatively large compared to most estuaries world-wide

40 High Suspended Sediment Levels Dynamic region of high turbidity

41 Suspended Sediment Levels Lower suspended sediments - clearer water Without Barrage Mean Flood - Spring Tide With Barrage

42 Effects of Turbidity Changes? But what type of birds? Dunlin or other birds?

43 Tidal Reef - Low Head Scheme Severn Embryonic Scheme Tidal reef design by Evans Engineering

44 Two-Way Generation: Peak Levels 764 Bulb Turbines No Sluices Without Barrage Without Barrage Reduced flood risk Continental Shelf Model Boundary Elevations With Barrage

45 Changes to Water Elevations 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

46 Water Level (m) Power output (GW) Water Level (m) Power output (GW) Water Levels and Power Output I II III II I=Filling (4.3h) 4m II=Holding (1.6h+1.0h) III=Generating (5.5h) Water level (m) Upstream of the barrage 2m Water level (m) Downstream of the barrage Power Generation Power Generation 24.4 Gwh 24.4 Gwh Time (hour) III I II III (c) (d) Water level (m) Upstream of the barrage I=Filling and Releasing (0.8h+1.1h) II=Holding (2.0h+1.3h) Power Generation 4m III=Generating (2.8h+4.4h) 2m Water level (m) Downstream of the barrage Power Generation 8.3 Gwh 15.9 Gwh 8.3 Gwh 15.9 Gwh Time (hour) (a) (a) 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

47 Lagoons: N Wales & NW England Need to be designed to minimise circulation Potential energy output of 26TWh/yr - 4h out of phase with Severn

48 Ebb-Only: Peak Currents 216 Bulb Turbines 166 Sluices (STPG) Without Barrage Continental Shelf Model Boundary Elevations With Barrage With Barrage

49 Two-Way: Peak Currents 764 Bulb Turbines No Sluices Without Barrage Continental Shelf Model Boundary Elevations With Barrage Similar to natural estuary

50 Ebb-Only Generation (STPG) 216 Turbines 166 Sluices

51 Two-Way Generation 764 Turbines No Sluices

52 Hafren Power Scheme 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?

53 Peak Water Levels (2025) 1026 VLH Turbines No Sluices Without Barrage Continental Shelf Model Boundary Elevations With Barrage

54 Peak Water Levels (2145) 1026 VLH Turbines No Sluices Sea level rise m Without Barrage Continental Shelf Model Boundary Elevations Bund and Barrage

55 Severn Region Options Scheme Power (GW) Energy (TWh/yr) Base Cost ( bn) Tidal Stream TEL 100 x Turbines Tidal Reef (Atkins) Cardiff-Weston DECC (STGP) Bridgwater Bay Lagoon Welsh Grounds Lagoon Swansea Bay Lagoon (Source: BBC 02/14) Table adapted from DECC study

56 Levelised Cost Comparison Hafren Power,

57 UK Relative Water Stress - EA Low water stress High water stress

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59 Summarising Tidal stream turbines Limited to site by 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)

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61 Thank You Professor Roger A. Falconer