Nebraska Wind Resources

1. Nebraska Wind Resources Dennis Elliott National Renewable Energy Laboratory Meeting with Nebraska Public Power District NREL/NWTC November 19, 2007

2. 2005 Nebraska Wind Resource Mapping Project Collaborative effort involving: • DOE/NREL Wind Powering America program • State of Nebraska • NREL’s wind resource group and expert consultants • AWS Truewind

3. http://www.eere.energy.gov/windandhydro/ windpoweringamerica/wind_maps.asp

5. Unvalidated wind speed maps generated by model for 70m and 100m heights

6. High-Resolution Wind Mapping Approach for Nebraska • Comprehensive modeling and validation process produced detailed wind resource maps with a spatial resolution of 200 m • AWS Truewind used a numerical weather model with climatic data and wind flow model to produce the preliminary maps • NREL and meteorological consultants validated preliminary maps of 50-m annual average wind resource using • Available high-quality wind measurement data • Experts knowledge of wind flow and wind resources in Nebraska • Final wind resource maps developed based on revision of preliminary maps from validation results

7. Logic of Numerical Mapping Method • Model Design and Outputs • MesoMap - created by AWS Truewind • A numerical weather model (MASS) coupled to a wind flow model (WindMap) and global weather, topographical, and land cover data • NCEP/NCAR Reanalysis (200-km grid) - most important global weather input for MASS • MASS simulates weather conditions (including winds) over 365 random days selected from a 15-year period • For Nebraska, MASS runs to 2.5 km and WindMap to 0.2 km • Model output grids provided to NREL for review and validation

8. Validation Process • NREL completed a spreadsheet used in the validation process • Each measurement location • Site coordinates and elevation • Measurement heights and period of record • Measured speed and power • Adjusted speed and power to map height • Map estimates for speed and power • Qualitative comments • NREL & AWS Truewind reviewed validation results • AWS Truewind adjusted preliminary maps based on quantitative and qualitative inputs

9. Nebraska Validation Over 50 measurement stations used for validation: 35 Airport (6-14 m) 8 UWRAP (40-50 m) 6 RAWS (6 m) 1 DOE/TCS (30 m) 1 State (40 m) 3 Proprietary (24-80 m) Estimated accuracy of final wind maps Within 10% of annual speed and 20% of annual power at 80% of individual sites

10. Annual average shear exponents can vary from 1/7 to 0.25, causing considerable uncertainty in vertical extrapolations of wind resource

11. Even if 50-m wind resource is known, potential variations in shear exponents cause considerable uncertainty in wind resource at heights of 80-100 m • Measured shear exponent at Goodland is 0.235, with much higher wind resource at 90 m than estimated by 1/7 shear estimate

12. High wind shear locations can have considerably higher capacity factors at 80-100 m than low shear locations, given similar capacity factors at 50 m • Goodland’s capacity factor of 42.5% at 90 m is considerably higher than would be estimated by using typical shears of 1/7 to 0.2

13. Quantifying Available Windy Landsand Wind Electric Potential • Class 3 and higher resource areas used as base for available windy lands • Potentially sensitive environmental lands excluded • Potentially incompatible land use excluded • Some additional lands excluded by other factors

14. Land Exclusions from Wind Potential • Potentially sensitive environmental lands: • National Park Service, Fish and Wildlife Service, Wilderness, and Recreation Areas on federal land (predominately Forest Service and BLM lands) • Some state and private environmental lands where data was available • Half of the remaining Forest Service and Department of Defense lands were excluded to represent current dedicated use of land • Potentially incompatible land use: • Urban areas, airports, wetlands and water bodies • Half of non-ridge forested areas • Other factors: • Slopes greater than 20% were excluded • A 3 km area surrounding environmental and land use categories that were completely excluded (except water bodies) was also eliminated • Small, isolated class 3 and greater resource areas were eliminated using a minimum density criteria

15. Wind Electric Potential Estimation • Distance from transmission lines and roads not included in windy land calculations • Windy land  electric potential • Direct conversion from sq. km to potential installed capacity - 5 MW per km2 of available windy land

16. Nebraska Wind Electric Potential (Installed Capacity) Total before exclusions Developable • Class 3 + 803 GW 764 GW • Class 4 + 162 GW 156 GW • Class 5 + 2.7 GW 2.5 GW • Class 6 + <0.1 GW <0.1 GW 5% of the raw Class 3+ lands excluded 3% of the raw Class 4+ lands excluded

17. Stations Selected for Analysis of Monthly and Diurnal Characteristics

23. Summary of Nebraska Wind Resources • Good resource areas (Class 4) are located throughout the state • Areas of excellent resource (Class 5) are dispersed over the northern half of the state. • Winter-Spring maximum wind resource • Prevailing wind directions are from west-northwest (winter) and from south (spring and summer) • Tall-tower measurements (up to 80-100m+) and remote sensing (sodar/lidar) needed to • Estimate the wind shear at elevated heights of 50-100m+ • Characterize wind resource at hub-heights of advanced wind turbines