Permitting Setbacks for Wind Turbines and the Blade Throw Hazard Scott Larwood California Wind Energy Collaborative UC Davis Doctoral Student California Wind Energy Collaborative • California Wind Energy Collaborative • 2004 Forum Palm Springs 2004 Forum Palm Springs
Organization • Purpose of Investigation • Setbacks for California Counties • Blade Failure Probabilities • Blade Throw Analyses • Conclusions California Wind Energy Collaborative • California Wind Energy Collaborative • 2004 Forum Palm Springs 2004 Forum Palm Springs
Purpose • Part of “Wind Plant Optimization” task for California Wind Energy Collaborative • Study and Report on permitting issues with regards to the blade throw hazard – Seemed to be based on maximum range and a function of turbine size – Setbacks vary county to county – Setbacks can limit revenue with modern turbine heights California Wind Energy Collaborative • California Wind Energy Collaborative • 2004 Forum Palm Springs 2004 Forum Palm Springs
Turbine Geometry Total Height Hub Height Rotor Diameter California Wind Energy Collaborative • California Wind Energy Collaborative • 2004 Forum Palm Springs 2004 Forum Palm Springs
Example Parcel • One kilometer square parcel • Setbacks are three times overall height • Spacing requirements for turbine wakes – Three-diameters crosswind – Ten-diameters downwind • Layouts for two turbine types – Vestas V-47, 660 kW, 47-m Ø, 50-m HH – GE 1.5s, 1.5 MW, 70.5-m Ø, 65-m HH California Wind Energy Collaborative • California Wind Energy Collaborative • 2004 Forum Palm Springs 2004 Forum Palm Springs
Vestas V-47 Layout Setback 3D in-row 3X overall spacing height 1 km sq. meter parcel 10- V47 turbines 10D row 50 meter Towers spacing Total Rating 6.6 MW Setback Prevailing 3X overall Wind height California Wind Energy Collaborative • California Wind Energy Collaborative • 2004 Forum Palm Springs 2004 Forum Palm Springs
GE 1.5s Layout 1 km sq. meter parcel 3- GE1.5s turbines 65 meter towers Total Rating 4.5 MW Setback 3X overall 2.9D in-row height spacing Setback 3X overall Prevailing height Wind California Wind Energy Collaborative • California Wind Energy Collaborative • 2004 Forum Palm Springs 2004 Forum Palm Springs
Setbacks for California Counties Property Line Dwelling Roads Reductions in Setbacks Alameda County 3x/300 ft (91 3x/500 ft (152 3x/500 ft (152 maximum 50% m), more on m), more on m), 6x/500 ft reduction from slope slope from I-580, building site or more on sloped dwelling unit but terrain minimum 1.25x, road setback to no less than 300 ft (91 m) Contra Costa County 3x/500 ft (152 1000 ft (305 m) None exceptions not m) spelled in ordinance can be filed with county Kern County 4x/500 ft (152 4x/1000 ft (305 1.5x With agreement m) <40 acres or m) off-site from adjacent not wind energy owners to no zone, 1.5x >40 less than 1.5x acres Riverside County 1.1x to adjacent 3x/500 ft (152 1.25x for lightly None Wind Energy m) to lot line traveled, Zones with dwelling 1.5x/500 ft (152 m) for highly traveled. Solano County 3x/1000 ft (304 3x/1000 ft (304 3x Setback waived m) adjacent to m) with agreement residential from owners of zoning, 3x from adjacent other zonings parcels with wind turbines California Wind Energy Collaborative • California Wind Energy Collaborative • 2004 Forum Palm Springs 2004 Forum Palm Springs
Blade Failure Probabilities • Types and Causes • References in the Literature • Alameda County Data • WindStats Data California Wind Energy Collaborative • California Wind Energy Collaborative • 2004 Forum Palm Springs 2004 Forum Palm Springs
Types and Causes • Types – Root connection failure – Partial failure from lightning – Failure at outboard aerodynamic device – Tower strike – Partial failure due to defect – Extreme load buckling • Causes – Unforeseen events out of design envelope – Failure of control system – Human error – Incorrect design for fatigue/ultimate loads – Poor manufacturing quality – Usually a combination of above California Wind Energy Collaborative • California Wind Energy Collaborative • 2004 Forum Palm Springs 2004 Forum Palm Springs
References in the Literature • Putnam 1948 – 1.25 MW turbine, 750 ft (230 m) throw • SERI 1979 – Analysis at 1.2 × 10 -2 per year • Eggwertz 1981 Sweden – Estimate of 10 -5 per year • De Vries 1989 Netherlands – Netherlands 2 × 10 -2 per year – Denmark 3 to 5 × 10 -3 per year – US 3 × 10 -3 per year California Wind Energy Collaborative • California Wind Energy Collaborative • 2004 Forum Palm Springs 2004 Forum Palm Springs
Alameda and WindStats Data • Operators in Alameda County notify Building Official of Blade Throw – Jan 2000 to Fall 2003, Kenetech 56-100s – 5.4 × 10 -3 blade failures/turbine/year • WindStats Quarterly Publication – Denmark 1993-2004; 3.4 × 10 -3 failures/turbine/year – Germany 1996-2004; 1.5 × 10 -2 failures/turbine/year Unclear if failure resulted in blade throw – No apparent time trends • Recommend using 10 -2 per year as baseline probability California Wind Energy Collaborative • California Wind Energy Collaborative • 2004 Forum Palm Springs 2004 Forum Palm Springs
Blade Throw Analyses • Simplified Model • Literature • Recommendations California Wind Energy Collaborative • California Wind Energy Collaborative • 2004 Forum Palm Springs 2004 Forum Palm Springs
Simplified Model • Turbine Tip Speed V 0 – V tip R = Ω θ – r cg Gravity • Projectile Release Ω Velocity Center of Gravity – V r y Impact = Ω 0 cg X 1 x – • Projectile Range in Vacuum – 2 V X = 0 sin 2 θ – 1 g • Projectile Maximum Range in Vacuum – 2 V 0 X max = – g California Wind Energy Collaborative • California Wind Energy Collaborative • 2004 Forum Palm Springs 2004 Forum Palm Springs
Literature • Eggwertz 1981 Sweden – Random Probability of blade failure position • MacQueen 1983 UK – Upper limit of tip speed 310 m/s – Comparison to lightning strikes in UK 10 -7 per year • Sørensen 1984 Denmark – Comprehensive aerodynamic analysis shows limitations of other models – Study of three turbines of increasing size • Eggers 2001 – Closed form solutions for impact probabilities California Wind Energy Collaborative • California Wind Energy Collaborative • 2004 Forum Palm Springs 2004 Forum Palm Springs
Sørensen 1.5-2.0 MW Turbine Blade Throw Probabilities 10.00 9.00 8.00 Fragment Turbine Heights 7.00 Blade Hazard Range 6.00 Fragment Hazard Range 5.00 Blade Max Range 4.00 Fragment Max Range Blade 3.00 2.00 Hazard is 10^-4 Probability 1.00 0.00 100% 150% 200% 250% 300% Nominal Tip Speed California Wind Energy Collaborative • California Wind Energy Collaborative • 2004 Forum Palm Springs 2004 Forum Palm Springs
Comparison of Analyses Maximum Range of Full and Partial Blade Throw for Nominal Operating Condition Range normalized by Overall Height 6.0 5.0 4.0 Full Blade 3.0 Blade Fragment 2.0 1.0 0.0 0 50 100 150 Overall Height (m) California Wind Energy Collaborative • California Wind Energy Collaborative • 2004 Forum Palm Springs 2004 Forum Palm Springs
Recommendations • Develop consistent analysis method to provide guidance on setbacks • Failure 10 -2 ; Overall hazard- 10 -6 (one in a million) • Study variety of current turbines • Use Sørensen’s model and Eggwertz probability and impact method • Determine probability and range for failure tip speeds • Validate with actual failure data and/or field test California Wind Energy Collaborative • California Wind Energy Collaborative • 2004 Forum Palm Springs 2004 Forum Palm Springs
Conclusions • Setbacks were based on collaboration with industry but not applied consistently • Current regulations can “squeeze out” modern turbines • Blade failure rate is surprisingly high and not showing improvement • Blade throw has been studied extensively but no setback guidance • Proposed approach to develop set back guidance California Wind Energy Collaborative • California Wind Energy Collaborative • 2004 Forum Palm Springs 2004 Forum Palm Springs
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