Energy From the Severn Estuary

Trinity College, Bristol, March 10 th 2007

Energy Extraction Technologies ●

Barrages

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Tidal Lagoons

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Tidal Stream

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Tidal Fences

Tidal Power – Lagoons (Pictures: WWF Wales)

Tidal Power – Tidal Streams (Picture: Tidal Generation Ltd)

Tidal Fences

Tidal Power – Lagoons (Pictures: Tidal Electric)

Tidal Power – Lagoons (Picture: WWF Wales) Pictures Courtesy Tidal Electric Ltd

Tidal Power - Lagoons Pictures Courtesy Tidal Electric Ltd

Summary of Lagoons ●

Energy claimed at 3.4p/kWh

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Large volumes of aggregates & transport required

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Uncertainties of sealing, sedimentation, seabed preparation & storm integrity

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Some environmental issues to be resolved (e.g. area of sea-bed usage, blockage to sea users, & fish entrapment)

Tidal Power – Tidal Streams (Picture: Marine Current Turbines Ltd)

Features of Tidal Stream ● ● ● ●

Short lead time

 less capital intensive

Modular

 income starts on installation of first unit

Low impact Competitive

 avoids main barrage env. issues  early farms in the region 7-8p/kWh ● BUT: ● The Severn resource is ~10-15% of that from a barrage ● Although some tidal stream resource may be extractable in addition to a barrage ● Foundations could double for offshore wind turbines

Environmental Impact ●

Controllable extraction

- modular units can be sited to minimise effects on shipping or fishing ●

No blockage

- marine life relatively undisturbed, zero to low mortality ●

Tidal heights not affected

- no effect on salinity, inter-tidal or sub-tidal zones ●

Some issues to be addressed

- rotor/mammal interactions, electromagnetic and acoustic noise emissions

Wind and Tidal Stream

Challenges of Tidal Stream ●

Harsh environment

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Pinning large loads to the sea bed

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Retrieval for maintenance in water up to 100m

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Sub-sea cabling and connections

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Grid capacity onshore Sea mammal interaction – uncertainties

Not an easy environment…..

Photo courtesy Seacore Ltd

Specialist Construction Equipment

Flow Turbulence

Current Velocity

3000 2500 2000 1500 1000 500 0 09:36:00 10:48:00 12:00:00 13:12:00

Time

14:24:00 15:36:00 16:48:00

Energy Flux

Power Density

6000 5000 4000 3000 2000 1000 0 09:36:00 10:48:00 12:00:00 13:12:00

Time

14:24:00 15:36:00 16:48:00

Maintenance Windows

 How much resource is there?

UK – up to 4GW  3 of these….

Potential Tidal Stream Sites

(Source: DTI UK Atlas of Marine Renewable Energy)

Systems already demonstrated (1) (Picture: Marine Current Turbines Ltd)

Systems already demonstrated (2) (Picture: IT Power Ltd.)

Systems already demonstrated (3)

Larger recent demonstrations Hammerfest Strom, Norway

Larger recent demonstrations ENERMAR 120kW Variable-pitch Darrieus (Italy)

Larger recent demonstrations Engineering Business 150kW Stingray reciprocator (UK)

Larger recent demonstrations Open Hydro Marine Current Turbines

Diversity of solutions…..

And more…

State of Tidal Stream Industry ●

Being led by the UK

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Strong UK Govt support for R&D & capital Many device concepts – no convergence as yet

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A few medium scale prototypes are in the sea: many more to follow Market entry costs are high – £10m min

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Commercial machines a few years off

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Some planning, environmental and grid capacity issues to be addressed

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An environmentally benign offering to the sustainability mix

Cables coming ashore at Cauldale and the new grid station

Emissions and Materials Consumption ● Cradle to grave assessment required ● Tidal Stream : shorter construction time, pay back quicker. Steel in construction is energy intensive but less aggregate and concrete ● Tidal Lagoons: very high aggregate demand but little ancillary infrastructure ● ● Tidal Barrages: large material requirement, transport and ancillary infrastructure e.g. roads, port facilities; long pay-back time

(Slide by Morgan Parry, WWF Wales)

Species and Habitat Impacts ● ● ● ● ● Tidal Stream Energy devices possible

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environmental appraisals currently being carried out on individual devices. Fish and mammals may avoid them, acoustic deterrence Tidal Fences: than individual devices, but not complete barrier like barrage greater obstacle to fish and mammals Tidal Lagoons: fish and mammals may avoid the area but risk of fish entrapment during flood generation Tidal Barrages : reduce tidal range creating a loss of habitats. Water quality reduced if dispersal/dilution inadequate. Barrier to fish movements

(Slide by Morgan Parry, WWF Wales)

Sediment Flow ● ● ● ● ● Tidal Stream Energy devices elsewhere

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current turbines currently being modelled in Strangford Lough and Tidal Fences

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considerable reduction in energy of water column but less than barrage Tidal lagoons Choice of location can reduce sedimentation in shipping channels : currents and wave patterns altered. Tidal barrage: nutrient flux upstream and downstream. Navigation impacts highly modified sediment regime and

(Slide by Morgan Parry, WWF Wales)