Tidal Energy from the Severn Estuary: Opportunities and Challenges

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1 Co-financed with the support of the European Union 1 ERDF Atlantic Area Programme Investing in our common future Tidal Energy from the Severn Estuary: Opportunities and Challenges Prof Roger Falconer, Dr Athanasios Angeloudis and Dr Reza Ahmadian Hydro-environmental Research Centre, School of Engineering, Cardiff University

2 Key Considerations Climate change & population growth increasing energy demand Tidal energy is predictable advantage compared to wind / waves Severn Estuary has second highest tidal range world-wide and 4hr out of phase with tidal phase along North Wales Coast Two key types of tidal energy generation: Tidal stream turbines Kinetic Energy: Power V V = Mean free-stream tidal current at location 3 Tidal impoundments Potential Energy: Power H = Water level difference across barrage / lagoon A = Plan surface area impounded by barrage/ lagoon (Severn Barrage: A 5 km 2 3% > Lake Garda) A H 2 2

3 Tidal Stream Turbines Key details: Rotor diameter = 3 x 15m Minimum depth = 25m to LAT Installed capacity = 1.2MW Capital cost = 3million/MW Installed - Ramsey Sound Resource assessment in Bristol Channel / Severn Estuary: Identification of appropriate location for tidal array farms Assessment of hydrodynamics and environmental impact of farms 3

4 Vertical Axis Turbines HRC Vertical Axis Turbine: Turbine is omni-directional Operates in shallower depths Blade designed to maximise lift: Increase torque Maximise efficiency Potential to site vertical axis turbines in barrage or lagoon wakes more power? 4 Annapolis Royal Barrage - Canada 1 x 2 MW turbine and 2 sluices

5 Earliest Severn Barrage Proposal First proposed by Thomas Fulljames

6 Existing Barrage Schemes - La Rance, France Key details: Completed in x 5.5m dia. bulb turbines & 6 sluices Turbine trials ebbonly (+ pumping) Generate.54TWh/y Energy cost 2/MWh cheapest in EU No baseline studies prior to construction 6

7 Tidal Barrages - Severn Barrage STPG Scheme STPG (1989) Severn Barrage Layout Barrage Location Cardiff - Weston Key facts of STPG scheme: 216 turbines 4 MW 16.4TWh/yr 166 sluice gates Length 16km Cost 23bn - base cost Ship locks Generate 5% of UK s electricity Save 7M tonnes of Carbon Designed to operate under an ebb-only generation regime 7

8 STPG Severn Barrage - Ebb-Only Generation Schematic Ebb Only 8 Level in impoundment

9 STPG Severn Barrage - Ebb-Only Generation Water levels upstream/downstream: Velocity magnitude without/with barrage Without Barrage 2 m/s water level(m) Flood Ebb 2 m/s water level(m) I II II III With Barrage (a) (a) Water level (m) Upstream of the barrage 4m m I=Filling (4.3h) 8 Water level (m) Downstream of the barrage II=Holding (1.6h+1.h) 6 III=Generating (5.5h) Power output (GW) Water Level (m) -4 Marked Reduction in Currents in Estuary 4 Power Generation Power Generation 24.4 Gwh Gwh Time (hour) Marked reduction in currents significant reduction in turbidity 9

10 STPG Severn Barrage - Hydro-environmental Impact But what type of birds? Dunlin or other birds? 1

11 Tidal Reef - Low Head (Minehead Aberthaw) Tidal reef design by 11 Evans Engineering

12 Severn Barrage - Two-Way Generation (Generic) Ebb Generation 48.8 GWh/24.8h 5.2 m mean tide High tide 4.6 m Power for 1h Ebb-only generation shows marked rise in groundwater levels Mean groundwater raised by 2m Two-way generation shows little change in groundwater levels Mean groundwater level unchanged Two-Way Generation 48.4 GWh/24.8h 4.4 m mean tide High tide 3.2 m Power for 17h Water Level (m) III I II III (d) Water level (m) Upstream of the barrage I=Filling and Releasing (.8h+1.1h) II=Holding (2.h+1.3h) 4m III=Generating (2.8h+4.4h) Power Generation 2m Water level (m) Downstream of the barrage Power Generation 8.3 Gwh 15.9 Gwh 8.3 Gwh 15.9 Gwh Time (hour) (c) Power output (GW) 12

13 DECC SETS Studies - VLH Two-Way Turbine Proposed Schematic Two Way Level in impoundment 13

14 Severn Barrage - Two-Way Generation Studies Severn Barrage two-way generation 764 bulb turbines and no sluices Tidal currents similar to those for no barrage Substantially less adverse impact than ebb-only generation Hafren Power Barrage Scheme (212) 126 VLH turbines - each 6.3 MW 16.4TWh/yr Designed for two-way generation Substantially less environmental change than for STPG scheme 14

15 Severn Barrage - Two-Way Generation Water levels upstream/downstream: Velocity magnitudes during operation: Severn Barrage scheme optimised to preserve dynamic nature of estuary Turbines and sluices regulated to minimize intertidal habitat loss and maximize power generation 15

16 Severn Barrage - Far Field Impacts Ebb-Only Two-Way Far field impacts significantly reduced for Two-Way generation 16

17 Tidal Lagoons - Fleming (Welsh Grounds) Proposal Welsh Grounds Lagoon (Xia and Falconer) Newport Deep Newport 6 Turbines 25 Sluices 25 Sluices Welsh Grounds Avonmouth Details (DECC,21): Area 8 km 2 Installed Capacity 136 MW Water level (m) Water level (m) Flood m/s 2 m/s Ebb Peak Power Output: a) -D analysis 1,3 MW b) 2-D model 9 MW with strong eddies Notice strong eddies Notice lower ebb current 17

18 Tidal Lagoons - Eddies Need to be Minimised Note how sediment accumulates at centre of eddy Before stirring After stirring Predicted to occur in Welsh Grounds (Fleming) Lagoon 18

19 Tidal Lagoons - Swansea Bay LW Swansea Bay Lagoon: Wall 9.7km long Area 11.6km x Cardiff Bay Novel design for embankment Energy output of.5-.6 TWh/yr HW 19

20 Tidal Eddies - Distribution of Hydraulic Structures Original Modified Wider distribution of turbines & sluices leads to weaker eddies Distributing momentum of flow through turbines & sluices over twice wall length significantly reduces wake effects etc. 2

21 Tidal Lagoons - North Wales (Idealised Design) Assessment of North Wales tidal lagoon options Offers major Coastal Protection Turbines & sluices along wall to reduce eddies 4 hours out of phase with Severn 21

22 Recent Research - Bristol Channel & Severn Estuary 22

23 Hydrodynamic Assessment Refinement Open source in-house models enable refinements to be made to turbine / sluice treatment etc. e.g. conservation of momentum through turbines Result A more sophisticated tool, tailored for hydro-environmental impact assessment studies for tidal range schemes 23

24 Tidal Impoundments - Operation Optimisation Impoundment Specifications & Tidal Conditions Hydraulic Turbine & Sluice Specifications Testing Operation Sequences Hydro-environmental Modelling Producing Summary of Operation Indicators Output Analysis Development of -D, 2-D optimisation tools adaptable to a range of sites Appreciation of turbine specification and impact of impoundment operation Identification and research on optimal operation for maximisation of power output and minimisation of environmental impacts 24

25 Tidal Impoundments - Case Studies -D Assessment Swansea Bay Lagoon Cardiff & Newport Lagoons Two-Way Severn Barrage Swansea Bay Lagoon Length: 9.6 km Area : 11.6 km 2 Capacity: 32 MW Quoted E:.5-.6 TWh/yr -D Capacity: 32 MW -D:.615 TWh/yr Cardiff Lagoon Length: 2.8 km Area: 65 km 2 Capacity: MW Quoted E: 4-6 TWh/yr -D Capacity: 21 MW -D: 5.28 TWh/yr Newport Lagoon Length: 16.4 Area: 32 km 2 Capacity: MW Quoted E: 2-3 TWh/yr -D Capacity: 12 MW -D: 3.5 TWh/yr 25 Severn Barrage (HRC) Length: 16.1 km Area : 573 km 2 Capacity: 16 MW Quoted: N/A -D Capacity: 16 MW -D: 36.6 TWh/yr

26 Tidal Lagoons - Hydrodynamic Modelling EBB Swansea Cardiff Newport FLOOD 26

27 Tidal Barrages - Hydrodynamic Modelling STPG Barrage - Ebb-only EBB HRC Barrage - Two-way FLOOD 27

28 Tidal Impoundments - Hydrodynamic Impacts General Findings:: Greater size of impoundment Greater impact on local hydrodynamic conditions Multiple schemes in close proximity have cumulative impacts multiple lagoons, or barrage and lagoons Impacts CAN be mitigated against through appropriate design of turbine and sluices requires optimised flow area for turbines and sluices Velocities Elevations 28

29 Tidal Impoundments - Power Generation Starting Head = 2.5m or Maximum holding time T = 1.5hr 29

30 Tidal Impoundments - Power Generation Comparative results for two-way generation operation using identical specifications Numerical Simulations Tidal Range Project Annual Energy (TWh/yr) Hydrodynamic Impact (%)* Swansea Bay Lagoon (SBL) Cardiff Lagoon (CL) Newport Lagoon (NL) Severn Barrage (HRC) -D Two-way D - SBL D - SBL,CL SBL CL NL HRC D - SBL,CL,NL Total Energy (TWh/yr) 2-D - HRC *Hydrodynamic impact refers to deviation from -D annual energy results, which takes no account of tidal impoundment impact on hydro-environment Optimisation for each scheme above yields more energy than in Table but with greater hydro-environmental footprint

31 Summarising Tidal Stream Turbines Limited to site around Minehead Aberthaw in Bristol Channel; Vertical axis turbines could be sited in impoundment wakes for increased energy? Tidal lagoons Require long wall for optimised area; Design critical for optimised hydrodynamics and environmental change Tidal Barrage Two-way generation could produce > 7% UK s electricity; Estuary flow features (e.g. inter-tidal habitats) could be preserved (particularly with pumping); Major flood risk reduction upstream; Port issues and fish migration remain challenging; Considerable scope for regional development Tidal Lagoons/Barrage interact in close proximity in Severn VLH Symmetric Turbines Offer considerable potential for future maximum power and minimum environmental change 31

32 Thank You Professor Roger A. Falconer