Energy From the Severn Estuary Trinity College, Bristol, March 10 th 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

Energy Flux

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 HydroMarine 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)