energy from the severn estuary trinity college bristol march 10 th 2007 l.
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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.

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energy extraction technologies
Energy Extraction Technologies
  • Barrages
  • Tidal Lagoons
  • Tidal Stream
  • Tidal Fences
tidal power lagoons picture wwf wales
Tidal Power – Lagoons(Picture: WWF Wales)

Pictures Courtesy Tidal Electric Ltd

tidal power lagoons
Tidal Power - Lagoons

Pictures Courtesy Tidal Electric Ltd

summary of lagoons
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
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 farmsin 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
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
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
how much resource is there
How much resource is there?
  • UK – up to 4GW
  • 3 of these….

Systems already demonstrated (1)

(Picture: Marine Current Turbines Ltd)


Systems already demonstrated (2)

(Picture: IT Power Ltd.)


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

state of tidal stream industry
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
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
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
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)