Energy From the Severn EstuaryTrinity College, Bristol, March 10th 2007

Energy Extraction Technologies

● Barrages● Tidal Lagoons● Tidal Stream● 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

● Large volumes of aggregates & transport required

● Uncertainties of sealing, sedimentation, seabed preparation & storm integrity

● 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 avoids main barrage env. issues

● Competitive 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

● Pinning large loads to the sea bed

● Retrieval for maintenance in water up to 100m

● Sub-sea cabling and connections

● Grid capacity onshore

● Sea mammal interaction – uncertainties

Not an easy environment…..

Photo courtesy Seacore Ltd

Specialist Construction Equipment

Flow Turbulence

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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 demonstrationsHammerfest Strom, Norway

Larger recent demonstrationsENERMAR 120kW Variable-pitch Darrieus (Italy)

Larger recent demonstrationsEngineering 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

● Strong UK Govt support for R&D & capital

● Many device concepts – no convergence as yet

● A few medium scale prototypes are in the sea: many more to follow

● Market entry costs are high – £10m min

● Commercial machines a few years off

● Some planning, environmental and grid capacity issues to be addressed

● 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: environmental

appraisals currently being carried out on individual devices. Fish and mammals may avoid them, acoustic deterrence possible

● Tidal Fences: greater obstacle to fish and mammals than individual devices, but not complete barrier like barrage

● 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: current turbines currently being modelled in Strangford Lough and elsewhere

● Tidal Fences: considerable reduction in energy of water column but less than barrage

● Tidal lagoons: currents and wave patterns altered. Choice of location can reduce sedimentation in shipping channels

● Tidal barrage: highly modified sediment regime and nutrient flux upstream and downstream. Navigation impacts

● (Slide by Morgan Parry, WWF Wales)