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