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Tidal In-Stream Energy Overview

Tidal In-Stream Energy Overview. Brian Polagye Research Assistant University of Washington Department of Mechanical Engineering. September 11, 2006. Agenda. Resource and Performance TISEC Devices Siting Arrays in Puget Sound UW Research.

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Tidal In-Stream Energy Overview

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  1. Tidal In-Stream Energy Overview Brian Polagye Research Assistant University of Washington Department of Mechanical Engineering September 11, 2006

  2. Agenda • Resource and Performance • TISEC Devices • Siting Arrays in Puget Sound • UW Research

  3. Tidal power is different than other forms of renewable energy Tidal Power - Comparison to Wind - Resource and Performance Wind Tidal Resource • Driven by uneven heating of earth’s surface by sun • Occurs throughout the world • Driven by gravitational pull of moon and sun • Highly localized - requiring specific tidal range and bathymetry Availability • Intermittent • Long-term predictions as good as a weather forecast • Intermittent • Predictable centuries in advance Proximity to Loads • Often distant from load centers • Often close to load centers • Mature technology • Developing technology Maturity 017,09-07-06,SNOPUD.ppt

  4. There are two very different approaches to harnessing the energy of the tides Resource and Performance Tidal Power - Utilizing the Resource - Barrage In-stream Tidal • Dam constructed across estuary • High cost ($ Bn) • Long construction period (decade) • Power produced by closing dam at high tide and allowing water to run through turbines once ocean has returned to low tide • Completely alters estuary circulation • Power produced in twice-daily surge • All attendant problems of hydro-electric dams • Low-cost power production at very large scale • Turbines installed in estuary at constrictions in groups called arrays • Moderate unit cost ($ MM) • Short unit construction time (weeks) • Power produced directly from tidal currents • More continuous (but still intermittent) power production • Smart choice of turbines and layout of arrays should avoid significant environment impact • Moderate-cost power production at varying scales 016,09-07-06,SNOPUD.ppt

  5. At a very basic level, tidal currents are generated by the rise and fall of the tides – water runs downhill Resource and Performance Tidal Currents Side View Top View Ocean Ocean Water level increasing Flood tide Tidal Basin Slack water Tidal Basin Ebb tide Water level decreasing Seabed • Slack water • Constant water height • No velocity • Flood Tide • Water level higher outside estuary than in main basin • Water flows into estuary • Ebb Tide • Water level higher in basin than ocean • Water flows out of basin 015,09-07-06,SNOPUD.ppt

  6. Spring Tides (strongest) Neap Tides (weakest) Tidal currents vary primarily on a fourteen day lunar cycle Resource and Performance Tidal Cycle 014,09-07-06,SNOPUD.ppt

  7. Flow power has a cubic dependence on velocity – small velocity changes have a large effect on power Device Performance - Resource Utilization - Resource and Performance Device Performance Representative Day Rated Speed Cut-in Speed 018,09-07-06,SNOPUD.ppt

  8. Power generation varies day-to-day, but is consistent on a monthly basis and shows no seasonal dependency Device Performance - Variable Predictability - Resource and Performance Daily Average Monthly Average 019,09-07-06,SNOPUD.ppt

  9. Agenda • Resource and Performance • TISEC Devices • Siting Arrays in Puget Sound • UW Research

  10. All turbines have a number of common components, but many variants TISEC Devices Turbine Overview Gearbox • Increase rotational speed of shaft from turbine • 80-95% efficient Generator and Power Conditioning Powertrain or Drivetrain • Generate electricity • Condition electricity for grid interconnection • Turns at high RPM • 95-98% efficient Rotor • Extracts power from flow • Turns at low RPM • Efficiency varies with flow velocity (45% max) Foundation • Secure turbine to seabed • Resist drag on support structure and thrust on rotor 009,09-07-06,SNOPUD.ppt

  11. Two basic types of rotors have been developed – horizontal axis and vertical axis TISEC Devices Rotor Variants Horizontal Axis Vertical Axis Gearbox and Generator Gearbox and Generator 013,09-07-06,SNOPUD.ppt

  12. Ducted turbines have been proposed to augment power production TISEC Devices Power Augmentation • Enclosing turbine in diffuser duct boosts power • A number of questions remain unanswered regarding this approach • Is it economically justified? • Ducts were never justified for wind turbines • Different set of circumstances for tidal turbines • Is there an increased hazard to marine mammals and fish? • Can a large fish or mammal become trapped in the duct? 012,09-07-06,SNOPUD.ppt

  13. Foundation selection is usually driven by site water depth TISEC Devices Foundation Types Monopile Gravity Base Heavy foundation of concrete and low cost aggregate placed on seabed Hollow steel pile driven or drilled into seabed Pros: • Deep water installation feasible Pros: • Small footprint • Established technology used in offshore wind Cons: • Large footprint • Scour problems for some types of seabed • Decommissioning problems Cons: • High cost in deep water • Installation expensive for some types of seabed (10-40m) Chain Anchors Chains anchored to seabed and turbine Tension Leg Submerged platform held in place by anchored cables under high tension Pros: • Small footprint • Deep water installation feasible Pros: • Small footprint • Deep water installation feasible Cons: • Problematic in practice • Device must have high natural buoyancy Cons: • Immature technology now being considered for offshore wind in deep water 010,09-07-06,SNOPUD.ppt

  14. TISEC Devices Maintenance Options Divers Divers service turbine • Marine intervention extremely costly and must be minimized if TISEC devices can hope to compete economically • All device developers pursuing low-maintenance philosophies Pros: • Divers widely available Cons: • Difficult to work underwater • Very high intervention cost • In deep water, dive time measured in minutes per day Device Retrieval Crane barge mobilized to retrieval entire turbine Integrated Lift Lifting mechanism integrated directly into turbine support structure Pros: • Maintenance without specialty craft • Deep water feasible Pros: • Less costly than divers • Deep water feasible Cons: • Cost of lifting mechanism • Support structure may be surface piercing (aesthetic and shipping concerns) Cons: • High cost to mobilize heavy-lift crane barge 011,09-07-06,SNOPUD.ppt

  15. Marine Current Turbines is furthest along in the development process TISEC Devices Marine Current Turbines (MCT) Horizontal axis (2 bladed) Planetary gearbox Induction generator Rated from 1.2 – 2.5 MW Power train Monopile drilled or driven into seabed Two turbines per pile Foundation Lifting mechanism pulls turbine out of water for servicing Maintenance 3 years of testing prototype in UK 1.5 MW demonstration planned for installation in 2006/2007 Conceptual fully submerged units Development Large Scale (18 m diameter) 002,09-07-06,SNOPUD.ppt

  16. Verdant is positioned to install the first array of TISEC devices in the world TISEC Devices Verdant Horizontal axis (3 bladed) Planetary gearbox Induction generator Rated at 34 kW Power train Foundation Monopile drilled or driven into seabed Retrieval of power train by crane barge Divers employed during installation Maintenance Small Scale (5 m diameter) Development Installing 6 turbines off Roosevelt Island, NY City (Starting mid-Sept) First permitted test project in US 002,09-07-06,SNOPUD.ppt

  17. Lunar Energy has adopted a different philosophy with an emphasis on a “bulletproof” design TISEC Devices Lunar Energy Horizontal axis (ducted) Hydraulic gearbox Induction generator Rated at 2 MW Power train Foundation Gravity foundation using concrete and aggregate Heavy-lift crane barge recovers “cassette” with all moving parts Maintenance Large Scale (21 m diameter inlet) Tank testing Nearing end of design for first large scale unit Development 001,09-07-06,SNOPUD.ppt

  18. Agenda • Resource and Performance • TISEC Devices • Siting Arrays in Puget Sound • UW Research

  19. Environmental issues are probably the biggest unknown for siting arrays of tidal in-stream turbines Case Study Siting Environmental Issues - Marine Life Considerations - Environmental Issue Answers (so far) Key Questions Direct “impact” of turbine on marine life • Will a turbine make sushi in addition to electricity? • No. Maximum tip velocity limited by cavitation. (~10 RPM for large turbines) • Unknown. Considerable cost and effort being expended by developers to prove technology is benign. No Altamont Passes. • Will the rotor injure or harass fish and marine mammals? Indirect impacts • Will anti-fouling paints used on turbines and supports degrade environment? • Developers are testing inert, glass-based anti-fouling paints to minimize this impact. • Will oils and lubricants leak from the turbine? • Not in large quantities, but developers are working to minimize any leakage. • How much of the seafloor will be disturbed during installation? • Depends on type of foundation and construction techniques. Choices will be driven by site depth and local concerns. 007,09-07-06,SNOPUD.ppt

  20. Case Study Siting Environmental Issues Environmental Issue Answers (so far) Key Questions Effect of energy extraction on the environment • What is the effect of energy extraction? • Altered circulation in estuary • Effects complicated and counter-intuitive • Velocity increases downstream of an array and water depth decreases • Overall flow rates are reduced • How much energy can be extracted without substantially altering circulation? • Rough estimates. 15% of the kinetic energy in a channel used as placeholder in resource studies. • Overly conservative in some cases, overly optimistic in others. • Question needs to be addressed on a case-by-case basis 008,09-07-06,SNOPUD.ppt

  21. In addition to environment, a number of factors need to be considered when siting turbine arrays. Most have not yet been addressed for sites in Puget Sound. Case Study Siting Array Siting Issues - General - Issue Status Key Questions Resource Size and Quality • How large is the extractable resource? • How many turbines in an array? • Preliminary estimates using NOAA single-point current predictions • Next Step: Current measurements Electrical Infrastructure • Will new transmission lines need to be built? • What local loads exist? • Not yet determined – requires consultation with local utilities Bathymetry and Seabed Geology • What foundation types are suitable for water depth? • What foundations can seabed support? • Not yet determined – requires geologic survey • Not an issue in Puget Sound for most types of construction Port Facilities • Are there local marine contractors capable of performing installation and maintenance of an array? 005,09-07-06,SNOPUD.ppt

  22. And the list goes on… Siting Case Study Array Siting Issues - General - Issue Status Key Questions Shipping Traffic • What is the maximum draft of shipping traffic in channel? • Not yet determined – requires consultations with marine exchange and Coast Guard Large-scale Turbulence • Are there local geographic features that would give rise to large-scale eddies? • Not yet determined – requires consultations with oceanographic experts Multiple Use • How is the site currently used? • Does the site overlap with major recreation or fishing areas? • Not yet determined – requires consultations with regional stakeholders Economics • Will turbines produce cost-effective power? • Tacoma Narrows study predicted a cost of energy of ~10 cents/kWh • Next step: Feasibility study 006,09-07-06,SNOPUD.ppt

  23. There are a number of prospective tidal energy sites in Puget Sound Puget Sound Resource Study - Overview - Siting Spieden Channel Power Density (kW/m2) Resource (MW) Depth (m) Guemes Channel Site • Tacoma Narrows 1.7 106 40 • Admiralty Inlet • Point Wilson • Marrowstone • Bush Point San Juan Channel 0.6 0.6 0.4 167 195 132 60 71 75 Deception Pass • Deception Pass • Deception Pass • Yokeko Point 5.5 0.4 26 3 30 16 Admiralty Inlet • Guemes Channel 1.5 35 14 • Bainbridge Island • Agate Passage • Rich Passage 1.5 0.9 3 9 6 15 Agate Passage • San Juan Islands • San Juan Channel • Spieden Channel 0.6 0.6 45 56 63 69 Rich Passage Tacoma Narrows estimated COE ~10 cents/kWh. Other sites? 020,09-07-06,SNOPUD.ppt

  24. San Juan Channel represents a substantial resource, but the channel is quite deep San Juan Channel - Overview - Siting Preliminary Array Layout Preliminary Turbine Layout 0.8 km (0.5 mi) Turbine + Lateral Spacing San Juan Channel Ref. 0.6 kW/m2 Preliminary Array Performance • 116 turbines (20 m diameter) • Average installation depth ~95m • 5 MW average electric power • 16 MW rated electric power • 39,900 MWh annual generation 024,09-07-06,SNOPUD.ppt

  25. Spieden Channel also represents a substantial resource, but is again a deep water channel Spieden Channel - Overview - Siting Preliminary Array Layout Preliminary Turbine Layout 1 km (0.6 mi) Limestone Point Ref. Preliminary Array Performance Turbine + Lateral Spacing 0.6 kW/m2 • 8 MW average electric power • 26 MW rated electric power • 62,700 MWh annual generation • 168 turbines (20 m diameter) • Average installation depth ~83m 025,09-07-06,SNOPUD.ppt

  26. Agenda • Resource and Performance • TISEC Devices • Siting Arrays in Puget Sound • UW Research

  27. Question 1: How much tidal energy can be environmentally extracted? Extraction Limits - Balancing Resource Against Environmental Impact - Case Study UW Research • How much kinetic energy can be extracted by an array? • Current estimates are 15% of kinetic energy in a channel (little physical reasoning) • Probably much more site specific and closely related to frictional losses in channel • Does the construction of one array preclude the construction of others? • Can 20+ MW arrays be built at Pt. Wilson, Marrowstone and Bush Point? • Can an array be built at Admiralty Inlet if one already operating in Tacoma Narrows? • Building an understanding with 1-D models • Very interesting preliminary results • Will be expanding to 2-D and 3-D cases Admiralty Head ? Point Wilson ? Marrowstone Point Indian Island Bush Point ? 003,09-07-06,SNOPUD.ppt

  28. Question 2: How tightly can turbines in an array be packed? Array Packing - Most Economic Use of Resource - Case Study UW Research • Regions of high power flux may be relatively short and narrow • How close is too close? • Since flow is bi-directional, wind turbine spacing rules are probably too conservative • Downstream turbines must be beyond wake of upstream turbines • Wakes degrade performance and accelerate metal fatigue • Approaching with a combination of analytical and computational tools • Little or no physical data available (since no arrays operating) • Plan to leverage results of CFD modeling to suggest “engineering rules” for array layouts Low Power Density Lopez Island High Power Density San Juan Island Low Power Density • Economic reasons to site as many turbines in high power density regions as possible 004,09-07-06,SNOPUD.ppt

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