Effects of Long-Distance Wakes Between Projects
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Transcript of Effects of Long-Distance Wakes Between Projects
Holly Hughes; Gordon Randall18 April 2012, EWEA Copenhagen
Effects of Long-Distance Wakes Between Projects
Effects of Long-Distance Wakes Between Projects
18 April 2012, EWEA Copenhagen
DNV KEMA Energy & Sustainability – who we are
Formed from the merger of DNV and KEMA in March 2012
More than 2,300 experts in 30 countries around the world advising and supporting organizations along the energy value chain
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Effects of Long-Distance Wakes Between Projects
18 April 2012, EWEA Copenhagen
Introduction
Purpose of presentation: Give an overview of DNV KEMA’s research and recommendations on long-distance wakes
First part of presentation: Measured long-distance (2+ km) wakes at operational wind farms
Second part of presentation: Recommendations and conclusions regarding siting
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Effects of Long-Distance Wakes Between Projects
18 April 2012, EWEA Copenhagen
Overview – how we measure wakes between projects
General methodologies- Option 1: Compare turbine
production or wind speeds before and after installation of upwind projects, relative to an unwaked control
- Option 2: Compare turbine production across a partially waked project, controlling for wind direction to change the waked and control turbines (provided you can distinguish between wakes and topographic effects)
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Effects of Long-Distance Wakes Between Projects
18 April 2012, EWEA Copenhagen
Overview of sites with observations
Variety of sites that have been looked at (all North America): - Pacific Northwest – unidirectional winds, rolling hilly terrain, low
turbulence- Upper Midwest – omnidirectional winds, flat terrain, generally low (but
variable) turbulence- South-central – one predominant direction, projects on mesas, generally
low (but variable) turbulence
Types of sites not yet looked at- Offshore – Have not (yet) had data from multiple nearby projects- Hilly, forested terrain – Not many cases of projects close to each other,
turbine arrangements often don’t facilitate analysis, and topographic effects and land cover often confuse matters
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Effects of Long-Distance Wakes Between Projects
18 April 2012, EWEA Copenhagen
Example 1: Unidirectional site, before/after comparison
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Winds unidirectional from west to east
Neighbouring project installed approximately 20 RD upwind, waking half of the front row of the original project
Downwind turbines operational for about 2 years without wakes
Effects of Long-Distance Wakes Between Projects
18 April 2012, EWEA Copenhagen
Example 1: Overall project performance before/after upwind project
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Effects of Long-Distance Wakes Between Projects
18 April 2012, EWEA Copenhagen
Example 2: Varied wind rose, wakes compared by direction
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Winds from all directions
Neighbouring project installed approximately 50 to 70 RD upwind, depending on wind direction
Depending on wind direction, either the north or south half of the downwind project is waked.
Effects of Long-Distance Wakes Between Projects
18 April 2012, EWEA Copenhagen
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Example 2: Wakes under different conditions (speed, direction dataset, etc.) measured compared to eddy viscosity model
30-50 RD modelled: 8.3%30-50 RD measured: 18.0%(Factor of 2.2)
50-70 RD modelled: 4.6%50-70 RD measured: 11.9%(Factor of 2.6)
Effects of Long-Distance Wakes Between Projects
18 April 2012, EWEA Copenhagen
Main conclusions from measurements
Significant wakes observed to travel >50 RD downwind under stable conditions
Many wake models tested against measurements (e.g., eddy viscosity) do not accurately characterize long-distance wakes – models consistently underestimated effects by about a factor of three
Not a “deep array effect” – large wake deficits were observed at long distances from only one or two upwind turbine rows
DNV KEMA has improved models incorporating wake and atmospheric observations – but the models are still dependent on having good data and knowing where future turbines will be
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Effects of Long-Distance Wakes Between Projects
18 April 2012, EWEA Copenhagen
Recommendations for siting: Site characterisation
Remote sensing/tall tower measurements up to and above top of rotor are useful for accurate wake modelling
Stability measurements are also useful (but not as much so)
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Effects of Long-Distance Wakes Between Projects
18 April 2012, EWEA Copenhagen
Considerations for siting: How far away are there “zero” wake effects from upwind projects?
No “wake-free” safe distance has been found – significant wakes were observed at 70 rotor diameters, so it’s some distance beyond that (at least at some sites)
“Safe” distances should consider sizes of future turbines – your project may have 70m rotors, but another developer’s upwind project could use 120m+ rotors: 70 rotor diameters = 8.4+ km
Land rights/setbacks of this distance are unlikely at many sites (and may be inefficient)
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Effects of Long-Distance Wakes Between Projects
18 April 2012, EWEA Copenhagen
Expected magnitudes of external wakes
Highly dependent on layouts, distances, turbine sizes, stability, atmospheric profiles, etc., so impossible to generalize, but…
To generalize:- Worst case with project 20 RD completely upwind (e.g.,
unidirectional wind rose) and low-moderate wind speeds, external wake losses >10% on AEP are likely
- Projects 40-60 RD upwind with varied wind roses/partial overlap could have approximately 1-2% effect on AEP
- Large downwind projects with large internal wakes will have less average incremental effect
…and keep in mind that 1% energy loss can have a huge effect on a project economics
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Effects of Long-Distance Wakes Between Projects
18 April 2012, EWEA Copenhagen
Recommendations for siting: establishing project setbacks
Requiring “zero” wakes is not really plausible at sites in regions conducive to large-scale wind development
Tolerance for external wakes is a project-specific decision – different lenders and equity partners will have different opinions
Calculating a “maximum external wake” loss assuming other developers build projects everywhere that’s feasible will probably give a grim result – but it is useful to know
Recommend tiered siting guidelines: “no-action” zone, “test” zone, “no-build” zone
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Effects of Long-Distance Wakes Between Projects
18 April 2012, EWEA Copenhagen
Tests to measure wakes – how to plan
Depending on the site layout and surrounding terrain, it can be difficult to plan ahead for measurements of wakes from as-yet-unknown turbines
Permanent mostly-unwaked meteorological masts can be useful, particularly in pairs (or more) to compare; remote sensing also useful
Wake measurements can’t be done quickly – may need a full year to capture varying atmospheric conditions and wind directions
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Effects of Long-Distance Wakes Between Projects
18 April 2012, EWEA Copenhagen
Example test case on mesa
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Existing project on mesa
Wind Rose
Permanent measurement
Wind turbine – existing project
No-build zone: 2 km to south, 1 km other directions
Test required out to 10 km south, 5 km other directions
Effects of Long-Distance Wakes Between Projects
18 April 2012, EWEA Copenhagen
Conclusions
There can be large impacts from external wakes on projects – much more than many current models indicate
Given modern turbine sizes, 8 km or more distance may be needed to avoid impacts
Good upfront data collection will help estimate potential effects and establish setbacks
External wakes can be measured effectively – with the right planning
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Effects of Long-Distance Wakes Between Projects
18 April 2012, EWEA Copenhagen
www.dnvkema.comVisit us at Stand C1-C9
Holly Hughes [email protected] +44 7817 639369