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Large Tidal Turbine Farms:

Large Tidal Turbine Farms:. A tale of two NZ channels. Sea-Gen . Ross Vennell Ocean Physics Group, Department of Marine Science, University of Otago ross.vennell@otago.ac.nz http://www.otago.ac.nz/oceanphysics.

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Large Tidal Turbine Farms:

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  1. Large Tidal Turbine Farms: A tale of two NZ channels Sea-Gen Ross Vennell Ocean Physics Group, Department of Marine Science, University of Otago ross.vennell@otago.ac.nz http://www.otago.ac.nz/oceanphysics R. Vennell, Tuning turbines in a tidal channel, Journal of Fluid Mechanics, 2010. R. Vennell, Tuning tidal turbines in-concert to maximise farm efficiency, Journal of Fluid Mechanics, 2011 R. Vennell, Estimating the Power Potential of Tidal Currents and the Impact of Power Extraction on Flow Speeds, Renewable Energy, 2011

  2. Two types tidal power 1) Tidal Barrage Require largetidal range > 5m Rare!! 1960’s, Worlds Largest 240 MW plant on the Rance River, France http://en.wikipedia.org/wiki/Tidal_power 2) Tidal Current Power Requires currents around 2m/s Common in straits and channels around the world High density energy at predictable times

  3. Tidal Current PowerTidal Turbines- wet wind turbines? Verdant Power – New York’s East River www.marineturbines.com 1.2MW at 2.25 m/s Open Hydro (Ireland) – Canada Kobold Vertical Axis Turbine – Straits of Messina, Italy

  4. Large Tidal Turbine Farms Different to Wind Farms Wind Farms are tiny compared to volume weather systems which drive then ->Farm does not affect free-stream flow NZ Met. Service • Tidal Turbine Farms must be densely packed within channel • Strong interaction between power extraction and flow -> affects free-stream flow • Power extraction slows currents along entire channel!

  5. ? 1MW 100 MW’s How does power output scale with farm size? Power extraction slows the flow -> power does not scale linearly!! Tidal current research and development Most: CFD modelling and building single turbines Few: estimating the limits of production from a given channel No one: connected the dots by determine how much power a given number of turbines can deliver from a channel

  6. Upper limit for Production in Channels Installed Capacity Farm Power Production Channel’s Upper Limit or Potential requires a “wall of turbines” Maximum realisable with gaps Decreasing Flow-> Number of Turbines -> Flow will bypass turbines through any gaps needed for navigation!

  7. Gaps to allow Navigation along ChannelBypassing flow and Mixing Losses Bypassing Flow Turbines Mixing Losses Channel Shoreline

  8. Yes there are equations!

  9. Two examples Kaipara Harbour Cook Strait EnergyScape, 2009

  10. Kaipara Harbour • Channel • 15 km long channel • 25 m deep • 2.5 km wide • Estuary • 950 km2 • 400km2 dry at low tide • 1.5-2.7m tidal range

  11. Kaiprara Harbour Entrance Based on 1.7m/s peak flows and 18m diameter turbine blades and assumes turbines are optimally tuned for the channel.

  12. Power production will be smaller as these values as they don’t allow for • Mechanical loses in gear boxes • Electrical conversion and transmission losses • Energy losses due to drag on turbine’s support structure (?) • Effects of upstream rows and their turbulence on turbine efficiency (?) • Energy dissipation with the shallow Harbour due to bottom friction (?)

  13. Cook Strait • Channel • 100 km long channel • 150+ m deep • 25 km wide • High tide at one end when almost low tide at the other

  14. Cook Strait Based on 1.1 m/s peak flows and 18m diameter turbine blades and assumes turbines are optimally tuned for the channel.

  15. Effect Of Current Speed on Turbine Output 1.2MW Power  V 3 Power Production of Sea Gen Filling more of Cross-section 2.25 m/s Rated Current 0.5MW 1.7 m/s Kaipara 0.14MW 1.1 m/s Cook Strait Current Speed Low currents low output per turbine large numbers of turbines required.

  16. Cook Strait Numbers Unduly Pessimistic • Install in high flow regions to reduce turbine numbers • These regions will move as a result, but should give higher flows that 1.1m/s cross-sectional average velocity. • Peter McComb- MetOceanSolutions

  17. Summary • A compromise between Power Production and • The fraction of the cross-section turbines are permitted to occupy • An environmentally acceptable flow reduction • For Kaipara, 250 18m diameter turbines give an average of 240 MW if channel cross-section filled with turbines and a 40% flow reduction 45 MW if only 10% of cross-section filled and a 5% flow reduction • For Cook Strait low average flows mean large numbers of turbines are needed, however targeting high flow regions would require far fewer turbines and yield 1-2GW ross.vennell@otago.ac.nz www.otago.ac.nz/oceanphysics R. Vennell, Tuning turbines in a tidal channel. Journal of Fluid Mechanics, 2010. R. Vennell, Tuning tidal turbines in-concert to maximise farm efficiency, Journal of Fluid Mechanics, 2011 R. Vennell, Estimating the Power Potential of Tidal Currents and the Impact of Power Extraction on Flow Speeds, Renewable Energy, in press

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