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….
slide22

Systems already demonstrated (1)

(Picture: Marine Current Turbines Ltd)

slide23

Systems already demonstrated (2)

(Picture: IT Power Ltd.)

slide25

Larger recent demonstrations

Hammerfest Strom, Norway

slide26

Larger recent demonstrations

ENERMAR 120kW Variable-pitch Darrieus (Italy)

slide27

Larger recent demonstrations

Engineering Business 150kW Stingray reciprocator (UK)

slide28

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)