Tidal In-Stream Energy Overview
Brian Polagye
Research Assistant
University of Washington
Department of Mechanical Engineering
March 6, 2007
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Agenda
• Tidal Energy Status
• TISEC Device Overview
• TISEC in Puget Sound
• UW Research
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Past development of the tidal resource has involved barrages
Status
Barrages
- Past Development -
• Dam constructed across estuary
requiring long construction time and
large financial commitment
• Power produced by impounding tidal
waters behind dam
• Drastically alters circulation of
estuary in addition to attendant
problems with conventional
hydroelectric
(constructed 1960)
• Low-cost power production at very
large scale
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250MW barrage in La Rance, France
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Present development interest is focused on free-stream turbines
Status
Tidal In-Stream Energy Conversion (TISEC)
- Present Development -
• Turbines installed in groups allowing
for more rapid, phased build-out
• Power produced directly from tidal
currents
• Should be possible to generate power
from tides with limited
environmental impact
• Moderate-cost power production at
varying scales
1.5 MW TISEC Device
(Marine Current Turbines)
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TISEC looks like the wind industry about twenty years ago
State of the Industry
Status
- Device Developers • More than a dozen device developers
― Dominant design has yet to emerge
― Most developers are UK based due to significant government
investment in marine renewables
• Many developers have tested small-scale models
― Laboratory and field tests to verify expected performance
― Difficult to address “big picture” questions in the lab
• Full-scale testing just beginning
― 300 kW turbine in water in Devon, UK for three years (MCT)
― 1.5 MW turbine planned for Strangford, UK in 2006/2007
(MCT)
― 6 x 34kW turbine array permitted for East River, NY in 2007
(Verdant)
― kW scale ducted turbine at Race Rocks, BC (Clean Current)
― OpenHydro testing at EMEC (European Marine Energy
Center) since December 2006
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Significant interest in developing this resource in Pacific Northwest
Status
State of the Industry
- Pacific NW Activities • Many applications have been filed for preliminary permits from the FERC (Federal
Energy Regulatory Commission)
― Permit gives applicant three years to study site and precedence for application of full permit
― Applications from utilities (municipal utilities given precedence) and site developers
― Permit is needed to hook device up to grid, but does not authorize construction and installation.
Subject to the same permitting requirement as any marine construction project.
• A number of studies have been recently carried out, most notably, the ERPI North
American Feasibility Study
― 8 prospective sites in US and Canada. For Washington, considered Tacoma Narrows
― EPRI also recently produced a report on the in-stream resource in southeast Alaska
• The FERC has recently awarded a number of preliminary permits in Puget Sound
― Tacoma Power: Tacoma Narrows (awarded early 2006)
― Snohomish PUD: Deception Pass, Agate Pass, Rich Passage, San Juan Channel, Spieden
Channel, Guemes Channel (awarded February 2007)
― Competing applications for development in Admiralty Inlet still pending decision
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Agenda
• Tidal Energy Status
• TISEC Device Overview
• TISEC in Puget Sound
• UW Research
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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
Powertrain
or Drivetrain
Rotor
• Extracts power from flow
• Turns at low RPM
• Efficiency varies with flow
velocity (45% max)
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Generator and
Power Conditioning
• Generate electricity
• Condition electricity for
grid interconnection
• Turns at high RPM
• 95-98% efficient
Foundation
• Secure turbine to seabed
• Resist drag on support structure
and thrust on rotor
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Foundation selection is usually driven by site water depth
TISEC Devices
Foundation Types
Monopile
Hollow steel pile driven or
drilled into seabed
Gravity Base
Pros: • Deep water installation
feasible
Pros: • Small footprint
• Established technology used
in offshore wind
(10-40m)
Chain Anchors
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
Chains anchored to seabed and
turbine
Pros: • Small footprint
• Deep water installation
feasible
Cons: • Problematic in practice
• Device must have high
natural buoyancy
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Heavy foundation of concrete
and low cost aggregate placed
on seabed
Tension Leg
Submerged platform held in
place by anchored cables under
high tension
Pros: • Small footprint
• Deep water installation
feasible
Cons: • Immature technology now
being considered for
offshore wind in deep water
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Ducted turbines have been proposed to augment power production
Power Augmentation
TISEC Devices
• Enclosing turbine in diffuser duct may
boost power but 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?
―Is screening of ducts feasible?
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Marine Current Turbines is furthest along in the development process
Marine Current Turbines (MCT)
Power train
TISEC Devices
Horizontal axis (2 bladed)
Planetary gearbox
Induction generator
Rated from 1.2 – 2.5 MW
Foundation
Monopile drilled or driven into seabed
Two turbines per pile
Maintenance
Lifting mechanism pulls turbine out of
water for servicing
Development
Large Scale
(18 m diameter)
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3 years of testing prototype in UK
1.5 MW demonstration planned for
installation in 2006/2007
Conceptual fully submerged units
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Verdant is positioned to install the first array of TISEC devices in the world
TISEC Devices
Verdant
Power train
Small Scale
(5 m diameter)
Horizontal axis (3 bladed)
Planetary gearbox
Induction generator
Rated at 34 kW
Foundation
Monopile drilled or driven into seabed
Maintenance
Retrieval of power train by crane barge
Divers employed during installation
Development
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Installing 6 turbines off Roosevelt
Island, NY City
First turbine in water producing power
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Lunar Energy has adopted a different philosophy with an emphasis on a
“bulletproof” design
Lunar Energy
Power train
Foundation
TISEC Devices
Horizontal axis (ducted)
Hydraulic gearbox
Induction generator
Rated at 2 MW
Gravity foundation using concrete and
aggregate
Maintenance
Heavy-lift crane barge recovers
“cassette” with all moving parts
Development
Tank testing
Nearing end of design for first large
scale unit
Large Scale
(21 m diameter inlet)
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GCK is developing a vertical-axis turbine
GCK (Gorlov Helical Turbine)
Power train
Foundation
Small Scale
Maintenance
TISEC Devices
Vertical axis (3 bladed)
Power train TBD
Rated at 7 kW
TBD – neutral buoyant platform
proposed for arrays, bottom mount
for single units
TBD – divers?
(1 m diameter)
Development
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Testing of single or multiple devices
from fixed platforms
Power take-off has been problematic
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Agenda
• Tidal Energy Status
• TISEC Device Overview
• TISEC in Puget Sound
• UW Research
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A number of prospective tidal energy sites have been identified in Puget Sound
Puget Sound
Puget Sound Site Identification
Guemes
Channel
Spieden
Channel
San Juan
Channel
Point Wilson
Deception
Pass
Agate
Passage
Rich
Passage
Marrowstone
Point
Tacoma
Narrows
Bush Point
Large resource
Strong currents
Small resource
Weaker currents
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700+ MW of tidal
resources identified
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Case 1: Deception Pass: Exceptional resource quality, small cross-section
Deception Pass Narrows
High Power
Region
Siting
Feasible Array Layout
• 20 turbines (10 m diameter)
• Average installation depth ~30m
• Exceptionally strong currents may
complicate installation and surveys
1 km
Preliminary Array
Performance
• 3 MW average electric power
2 km
• 11 MW rated electric power
• Power for 2000 homes
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Case 2: Admiralty Inlet: Moderate resource quality, large cross-section
Admiralty Inlet
Siting
Feasible Array Layout
3 km
0.9 km
• 450 turbines (20 m diameter)
• Average installation depth ~60m
• Given lower power density can
installation be economic?
Preliminary Array
Performance
• 20 MW average electric power
• 68 MW rated electric power
• Power for 15,000 homes
Key Next Step
• Velocity survey of Admiralty Inlet
to refine power estimates
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Case 3: Tacoma Narrows: High resource quality, moderate cross section
Tacoma Narrows
Siting
Bathymetry
Study Array Layout
• 64 turbines (2x18 m diameter)
• Average installation depth ~56m
Point Evans Ref.
Study Array Performance
• 14 MW average electric power
Dual Rotor
Turbine Footprint
• 46 MW rated electric power
• Power for 11,000 homes
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The question of where to site turbines is a relatively complex one
Siting
Siting Decision Tree
Is there an instream resource?
No
Is there a low-cost
interconnection
point?
Yes
>60m
How deep is the
water?
<10m
Yes
Are there marine
construction
facilities?
Moderate Depth
Can seabed
support
foundation?
No
Are there other
stakeholders?
No
Yes
Large-scale
turbulence?
Yes
No
Yes
Yes
Marine traffic in
area?
No
Most/All
How much of
channel occupied?
Limited
No
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No
Yes
Potential for
multiple use?
No
Yes
OK to Build
Environmental considerations?
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Environmental issues usually dominate the discussion and the key questions may
be harder to identify, much less answer
Siting
Environmental Issues
Death of or
injury to fish
and marine
mammals
• Will a turbine make sushi in
addition to electricity?
• Will the rotor injure or harass
fish and marine mammals?
• Will turbine operation
alter sedimentation
patterns?
Fluidic impact of
energy extraction
• Will the tidal range be
altered?
• Toxicity of anti-fouling paints
and lubricants?
Local
environmental
degradation
• Does turbine operation cause
acoustic harassment?
• How will turbine operation
and installation affect salmon
recovery?
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• Will flow rates in the
estuary be reduced?
• Mudflat ecosystems?
Ecological
implications of
fluidic impacts
• Oxygen levels in south
Sound and Hood Canal?
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Agenda
• Tidal Energy Status
• TISEC Device Overview
• TISEC in Puget Sound
• UW Research
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Research Question: How much tidal energy can be extracted?
Extraction Limits
- Balancing Resource Against Fluidic Impact -
?
Point
Wilson
UW
Case
Research
Study
• How much kinetic energy can be extracted by
an array?
Admiralty
Head
― Current estimates are 15% of kinetic energy
in a channel (little physical reasoning)
― Preliminary results indicate limits are site
specific, but also indicate it may be possible
to “tune” turbines to site to minimize impact
?
• Does the construction of one array preclude
the construction of others?
Marrowstone
Point
Indian Island
Bush Point
?
― 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
― Validating 1-D results
― 2-D modeling work planned in conjunction
with SnoPUD
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