wind energy_meteorology_unit_8_-_offshore_wind_energy_meteorology

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Offshore_wind_energy_meteorology
Dr. Detlev Heinemann
http://www.energiemeteorologie.de/25488.html

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wind energy_meteorology_unit_8_-_offshore_wind_energy_meteorology

  1. 1. Carl von Ossietzky Universität Oldenburg Institute of Physics • Energy Meteorology Group Dr. Detlev Heinemann Offshore Wind Energy Meteorology Detlev Heinemann Carl von Ossietzky Universität Oldenburg Institute of Physics/Energy Meteorology Group ForWindMittwoch, 15. Juni 2011
  2. 2. OFFSHORE WIND ENERGY METEOROLOGY CONTENTS ‣ Introduction: Offshore-specific situation ‣ Characteristics of marine boundary layers ‣ Air-sea interaction (wind & waves) ‣ Momentum & Heat fluxes ‣ Vertical wind profiles over sea ‣ Turbulence ‣ Implications for wind power applications ‣ Consequences for modeling offshore wind speed profiles ‣ „OffshoreGrid“: Mescoscale calculation of offshore wind power ‣ Outlook & future researchMittwoch, 15. Juni 2011
  3. 3. OFFSHORE WIND ENERGY METEOROLOGY A GENERAL REMARK Basic Physics Assumptions on Description of Parameterizations Models atmospheric flow MBL flow MeasurementsMittwoch, 15. Juni 2011
  4. 4. OFFSHORE WIND ENERGY METEOROLOGY A GENERAL REMARK Basic Physics Assumptions on Description of Parameterizations Models atmospheric flow MBL flow MeasurementsMittwoch, 15. Juni 2011
  5. 5. OFFSHORE WIND ENERGY METEOROLOGY A GENERAL REMARK Basic Physics Assumptions on Description of Parameterizations Models atmospheric flow MBL flow Measurements mostly proven for non-complex onshore wind flowMittwoch, 15. Juni 2011
  6. 6. OFFSHORE WIND ENERGY METEOROLOGY A GENERAL REMARK Basic Physics Assumptions on Description of Parameterizations Models atmospheric flow MBL flow Measurements mostly proven for non-complex onshore wind flow Finite knowledge of offshore wind conditions limits our modeling success!Mittwoch, 15. Juni 2011
  7. 7. OFFSHORE WIND ENERGY METEOROLOGY ONSHORE (INLAND) vs. OFFSHORE (MARINE) Marine winds are fundamentally different from inland winds in four principal ways: Still vs. Moving Surface Atmospheric Stability ‣ Water surface moves in three dimensions ‣ Numerical models handle both high under the influence of wind forcing stability and high instability poorly due to their boundary layer parameterizations ‣ It has momentum from tides, ocean currents, and wind-driven currents ‣ Frictional turning: Highly variable over water (from near-geostrophic flow to highly ‣ Momentum transfer from wind is also ageostrophic flow); linked to wave height principal energy source of wave generation and stability Isallobaric Winds Land-Water Interface ‣ Local wind effect due to time-varying ‣ Varying coastal wind effects pressure fields ‣ Greater significance for marine wind field ‣ Regionally important due to decreased friction > larger cross- ‣ Include: Terrain-forced ageostrophic flows, isobar direction of the total wind vector onshore frictional (cyclonic) turning of the wind, atmospheric wave generation, cold ‣ Potential source of large wind forecast air damming, flow reversals and stalls errorsMittwoch, 15. Juni 2011
  8. 8. OFFSHORE WIND ENERGY METEOROLOGY MARINE BOUNDARY LAYER CONDITIONS Height extension ‣ Higher moisture content of marine air masses >> Lower lifting condensation level (LCL) than continental air masses >> Marine boundary layer (MBL) is rather shallow compared to continental air masses ‣ However, convective marine and stratocumulus topped boundary layers have active mixing processes. Both often provide moisture to the atmosphere from evaporation and simultaneously deepen by entrainment and mixing.Mittwoch, 15. Juni 2011
  9. 9. OFFSHORE WIND ENERGY METEOROLOGY MARINE BOUNDARY LAYER CONDITIONS Frictional Influences Lower frictional interactions impact wind direction ‣ For the same geostrophic forcing, winds over the water will have a different direction than those same winds found over land. ‣ Frictional effects result in the over-water winds not having as much of a cross-isobar direction as those over land. ‣ It is more likely that winds will be geostrophic and of a greater speed than a comparable setting over land (exception: high seas conditions).Mittwoch, 15. Juni 2011
  10. 10. OFFSHORE WIND ENERGY METEOROLOGY MARINE BOUNDARY LAYER CONDITIONS Sea Surface Temperatures (SST) Relatively unchanging sea surface temperature on diurnal time scales impacts lapse rates ‣ SSTs varies much less in space and time than temperatures over land. ‣ The ocean is also a nearly unlimited energy source and energy sink. ‣ Combined, these two attributes can quickly serve to modify the temperature and relative humidity of the MBL when air masses move off-shore. ‣ Over open water, the same properties generally create a much smaller diurnal oscillation in air temperature. ‣ Negative lapse rates (i.e., an inversion) due to nocturnal radiation cooling that are often seen over land are seldom experienced over the ocean.Mittwoch, 15. Juni 2011
  11. 11. OFFSHORE WIND ENERGY METEOROLOGY MARINE BOUNDARY LAYER CONDITIONS Momentum Transfer ... and the dynamics involved in creating waves ‣ Winds over the ocean are in contact with a moving surface into which they impart momentum resulting in wave generation. ‣ In turn, the sea surface roughness influences the surface wind. ‣ Marine winds are highly subject to boundary-layer processes such as mechanical and convective turbulence as well as stratification, and these processes control the momentum transfer into wave energy.Mittwoch, 15. Juni 2011
  12. 12. OFFSHORE WIND ENERGY METEOROLOGY MARINE BOUNDARY LAYER CONDITIONS MBL Issues in NWP Most of current NWP models have high vertical resolution in the boundary layer (up to 15 levels) But: Main errors in model BL profiles of wind, temperature, and dewpoint can be attributed to turbulence and convective parameterizations Further limitations: ‣ Simple algorithms for wind-wave coupling ‣ Lack of real-time data for model initialization (> data assimilation, > remote sensing) poor resolution of near-surface variables forecast winds (and waves) are often erroneous during both stability extremes in the MBLMittwoch, 15. Juni 2011
  13. 13. OFFSHORE WIND ENERGY METEOROLOGY MARINE BOUNDARY LAYER CONDITIONS MBL affects surface wind speed and direction differently than over land ‣ Friction at the ocean surface is the direct result of the transfer of turbulent kinetic energy (hence related to speed squared) from the wind field to the sea surface and wave field ‣ Magnitude of friction is dependent on stability and whether mechanical turbulence and/or convective turbulent processes are involved ‣ Stability is crucial in determining the wind-wave frictional couplingMittwoch, 15. Juni 2011
  14. 14. OFFSHORE WIND ENERGY METEOROLOGY MARINE BOUNDARY LAYER CONDITIONS MBL affects surface wind speed and direction differently than over land Friction shifts the wind away from geostrophic flow creating cross-contour flow toward lower pressure. The effects of the frictional force diminish with height until the wind is in a non-frictional dynamic state > geostrophic flow at the top of the boundary layer With less friction over sea, winds at the surface are stronger, more consistent Balance of boundary layer flow and more geostrophic in both speed The pressure gradient force Fp,h is balanced by the sum and direction as over land given the of the Coriolis force Fc,h and the friction force Ffr. same atmospheric conditions.Mittwoch, 15. Juni 2011
  15. 15. OFFSHORE WIND ENERGY METEOROLOGY MARINE BOUNDARY LAYER CONDITIONS Turbulence (I) Mechanical Turbulence ‣ through interaction of the wind and surface air mass with sea surface waves ‣ Resulting eddies formed by the rising and falling sea surface can extend vertically for tens of meters. ‣ Extent of eddies based on wave height and vertical near-surface wind shearMittwoch, 15. Juni 2011
  16. 16. OFFSHORE WIND ENERGY METEOROLOGY MARINE BOUNDARY LAYER CONDITIONS Turbulence (II) Thermal (convective) Turbulence ‣ Due to rising plumes of warm air and compensating downdrafts ‣ Range from 100 to more than 1000 m height ‣ Stability is the main factor for the depth of frictional coupling in the MBL due to convective turbulence ‣ Stratified lower atmosphere: Mixing is minimal and the surface air mass will be decoupled from the winds aloft ‣ Unstratified (i.e. unstable) atmosphere: Mixing couples winds aloft to the surface ‣ Temperature difference between rather constant SST and temperature of overlying air mass is primary factor impacting stability over waterMittwoch, 15. Juni 2011
  17. 17. OFFSHORE WIND ENERGY METEOROLOGY DIFFERENCES BETWEEN MARINE AND CONTINENTAL ATMOSPHERIC BOUNDARY LAYERS (I) ‣ Near-surface air is always moist, relative humidity typically ~ 75–100% ‣ Weak diurnal cycle, since surface energy fluxes distribute over a large depth (10–100+ m) of water (large heat capacity!) ‣ Small air-sea temperature differences, except near coasts. Air is typically 0–2 K cooler than the water due to radiative cooling and advection, except for strong winds or large sea-surface temperature (SST) gradients. ‣ The MBL air is usually radiatively cooling at 1–2 K/day, and some of this heat is supplied by sensible heat fluxes off the ocean surface. If the air is much colder than the SST, vigorous convection will quickly reduce the temperature difference.Mittwoch, 15. Juni 2011
  18. 18. OFFSHORE WIND ENERGY METEOROLOGY DIFFERENCES BETWEEN MARINE AND CONTINENTAL ATMOSPHERIC BOUNDARY LAYERS (II) ‣ Small ‘Bowen ratio’ of sensible to latent heat flux due to the small air-sea temperature difference: latent heat fluxes: ~ 50–200 Wm-2, sensible heat fluxes: ~ 0–30 Wm -2 ‣ Most of marine boundary layers include clouds. Excepting near coasts, when warm, dry continental air advects over a colder ocean, tending to produce a more stable shear-driven BL which does not deepen to the LCL of surface air. Clouds can greatly affect MBL dynamics. It also affects the surface and top- of-atmosphere energy balance and the SST.Mittwoch, 15. Juni 2011
  19. 19. OFFSHORE WIND ENERGY METEOROLOGY AIR-SEA MOMENTUM TRANSFER Basics ‣ When mean flow momentum ρu varies in the vertical, fluctuating vertical eddy motions of velocity w′ transport faster fluid from the momentum-rich region, which locally appears as excess velocity, positive u′. ‣ Averaged, the effects of these eddy motions add up to eddy transport of momentum, ρu′w′, (Reynolds flux of momentum or Reynolds stress) ‣ From the similarity principle of turbulence, the Reynolds stresses should be proportional to density times the square of the velocity scale: −ρu′w′ = const.ρu′2 (with velocity scale ( (u′2) ) 1/2) ‣ Other reasonable choice for the velocity scale is the “friction velocity” u* = (-u′w′) 1/2 ‣ Particularly useful for low level airflow where the Reynolds stress is nearly constant and differs little from τi , the effective shear force on the interface, e.g., the momentum flux from air to water: u* = (τi/ρ) 1/2Mittwoch, 15. Juni 2011
  20. 20. OFFSHORE WIND ENERGY METEOROLOGY AIR-SEA MOMENTUM TRANSFER Basics ‣ When mean flow momentum ρu varies in the vertical, fluctuating vertical eddy motions of velocity w′ transport faster fluid from the momentum-rich region, which locally appears as excess velocity, positive u′. ‣ Averaged, the effects of these eddy motions add up to eddy transport of momentum, ρu′w′, (Reynolds flux of momentum or Reynolds stress) ‣ From the similarity principle of turbulence, the Reynolds stresses should be proportional to density times the square of the velocity scale: −ρu′w′ = const.ρu′2 (with velocity scale ( (u′2) ) 1/2) ‣ Other reasonable choice for the velocity scale is the “friction velocity” u* = (-u′w′) 1/2 ‣ Particularly useful for low level airflow where the Reynolds stress is nearly constant and differs little from τi , the effective shear force on the interface, e.g., the momentum flux from air to water: u* = (τi/ρ) 1/2 ‣ ...finally, these considerations lead us to the well-known logarithmic wind profile.Mittwoch, 15. Juni 2011
  21. 21. OFFSHORE WIND ENERGY METEOROLOGY CHARNOCK‘s RELATION FOR WAVE INFLUENCE H. Charnock: Wind stress on a water surface. Quart. J. Roy. Meteorol. Soc. 639– 640, 1955. ‣ Charnock suggested that the roughness length of airflow over ocean waves should depend on acceleration of gravity g and surface stress/friction velocity u* ~ τ1/2 ‣ Dimensional considerations then gave rise to the Charnock relation for the roughness length ‣ Assumption: Sea state is completely determined by the local friction velocity u∗ u2 z 0 = Ac ∗ g ‣ Ac is a „constant“. But is actually not constant and depends on local state of sea. For the open ocean usually a value of Ac = 0.011 is generally used. In the coastal sea around Denmark a value of Ac = 0.018 has been found (Johnson et al., 1998).Mittwoch, 15. Juni 2011
  22. 22. OFFSHORE WIND ENERGY METEOROLOGY CHARNOCK‘s RELATION Dependence on Fetch (Johnson et al., 1998) ‣ z0 shows a dependence on wave age (the ratio between the phase speed of the dominant wave (c) and u*) ‣ The dependence on (inverse) wave age is often formulated as Ac = α(u∗ /c)β with α=1.89 and β=1.59. ‣ A fetch-dependent variation of c is: 2π xg 1/3 c/u∗ = ( ) 3.5 U10 with the fetch x and U10, the wind speed at 10 m height. ‣ A modification for all fetches leads to (u∗ /c)β with γ=69. Ac = α 1 + γ(u∗ /c)β+2Mittwoch, 15. Juni 2011
  23. 23. OFFSHORE WIND ENERGY METEOROLOGY CHARNOCK‘s RELATION Charnock constant Ac as a function of wave age c/u* ‣ Measurements taken from literature ‣ Fits from Johnson et al. (1998) H.P. Frank et al. (2000)Mittwoch, 15. Juni 2011
  24. 24. OFFSHORE WIND ENERGY METEOROLOGY CHARNOCK‘s RELATION Sea surface roughness as a function of wind speed at 10 m a.g.l. at different distances x from the coast using Charnock‘s relation with constant Ac = 0.018 and the wave age (i.e. fetch- 1 mm dependent) Charnock constant. u < 2.5 ms-1: water surface is approximately aerodynamically smooth >>viscous formula for z0 applies intermediate wind speeds: flow is aero- dynamically smooth over some parts of the water surface but rough around and in the lee of the breaking whitecaps basic graph: H.P. Frank et al. (2000) u > 10 ms-1: fully rough flowMittwoch, 15. Juni 2011
  25. 25. OFFSHORE WIND ENERGY METEOROLOGY CHARNOCK‘s RELATION Sea surface roughness as a function of wind speed at 10 m a.g.l. at different distances x from the coast using Charnock‘s relation with constant Ac = 0.018 and the wave age (i.e. fetch- 1 mm dependent) Charnock constant. u < 2.5 ms-1: water surface is rough flow > Charnock relation approximately aerodynamically smooth >>viscous formula for z0 applies intermediate wind speeds: flow is aero- dynamically smooth over some parts of the water surface but rough around and in the lee of the breaking whitecaps basic graph: H.P. Frank et al. (2000) u > 10 ms-1: fully rough flowMittwoch, 15. Juni 2011
  26. 26. OFFSHORE WIND ENERGY METEOROLOGY CHARNOCK‘s RELATION ‣ Charnock‘s formula is reasonably accurate for 10 m wind speeds of 4–50 ms-1. ‣ For 10m wind speeds of 5–10 ms-1, this gives roughness lengths of 0.1–1 mm, much less than almost any land surface. Even the heavy seas under in a tropical storm have a roughness length less than mown grass! ‣ This is because (a) the large waves move along with the wind, and (b) drag seems to mainly be due to the vertical displacements involved directly in breaking, rather than by the much larger amplitude longs well. ‣ The result is that near-surface wind speeds tend to be much higher over the ocean, while surface drag tends to be smaller over the ocean than over land surfaces.Mittwoch, 15. Juni 2011
  27. 27. OFFSHORE WIND ENERGY METEOROLOGY SENSIBLE AND LATENT HEAT TRANSFER AT THE AIR-SEA INTERFACE ‣ Usually heat transfer proceeds from the ocean to the atmosphere (only under rare conditions in reverse) as “sensible” and latent heat transfer via the molecular processes of conduction and diffusion ‣ Sensible heat raises or lowers air temperature ‣ Bulk of heat transfer from the sea to the atmosphere occurs via evaporation and the attendant transfer of latent heat ‣ In turbulent flow, Reynolds fluxes of temperature w′θ′ and of humidity w′q′ are the main vehicles of heat and vapor transport to or from the interface on the air side ‣ But: Different from momentum transfer molecular conduction or diffusion has to perform the transfer at the interface >> conductive or diffusive boundary layers confined by eddy motion ‣ This results in a complex interplay among molecular conduction and diffusion, wind waves, and the eddies of the turbulent air flowMittwoch, 15. Juni 2011
  28. 28. OFFSHORE WIND ENERGY METEOROLOGY SENSIBLE AND LATENT HEAT TRANSFER AT THE AIR-SEA INTERFACE ‣ In the constant stress layer, Reynolds fluxes of heat and humidity, w′θ′ and w′q′, are (very nearly) equal to the mean interface fluxes Qi/ρacpa and E/ρa (also a constant flux layer) ‣ Gradients of mean temperature then depend only on the temperature flux and the two scales of turbulence: dθ/dz = f(w′θ′,u∗,z) ‣ Heat transfer law, connecting interface flux (through the temperature scale θ∗=−w′θ′/u∗) to the temperature excess/deficiency θ(h)−θs: (θ(h) − θs) / θ∗ = κ−1 ln(h/zt) with zt analogue to z0 for the momentum transfer ‣ Same for humidity...Mittwoch, 15. Juni 2011
  29. 29. OFFSHORE WIND ENERGY METEOROLOGY SENSIBLE AND LATENT HEAT TRANSFER AT THE AIR-SEA INTERFACE ‣ If buoyancy effects are significant, then temperature gradient in the constant flux layer depends on L, as well as on θ∗ and u∗ (again analogue to momentum, same for humidity) dθ θ∗ z = φt ( ) dz κz LMittwoch, 15. Juni 2011
  30. 30. OFFSHORE WIND ENERGY METEOROLOGY VERTICAL WIND PROFILE OVER SEA ‣ Generally, Monin-Obukhov theory has been found to be applicable over open sea (although developed over land...) ‣ We need: homogeneous and stationary flow conditions u∗ z z u(z) = [ln( ) − Ψm ( )] κ z0 L ‣ Coastal areas show strong inhomogeneities due to – roughness change at coastline – heat flux change through different surfaces ‣ Common example: Warm air advection over cold water (> well-mixed layer below an inversion) ‣ Systematic deviations from Monin-Obukhov theory at offshore sites expected!Mittwoch, 15. Juni 2011
  31. 31. OFFSHORE WIND ENERGY METEOROLOGY VERTICAL WIND PROFILE OVER SEA Example: Ratio of wind speeds at 50m and 10m as a function of stability parameter 10/L for different estimation methods for L (1) Sonic method Directly from sonic anemometer measurements of friction velocity and heat flux: u3∗,s L=− g κ T w¯ s T with the covariance of temperature and vertical wind speed fluctuation w‘T‘ at the surfaceMittwoch, 15. Juni 2011
  32. 32. OFFSHORE WIND ENERGY METEOROLOGY VERTICAL WIND PROFILE OVER SEA Example: Ratio of wind speeds at 50m and 10m as a function of stability parameter 10/L for different estimation methods for L But how to determine L? (1) Sonic method Directly from sonic anemometer measurements of friction velocity and heat flux: u3∗,s L=− g κ T w¯ s T with the covariance of temperature and vertical wind speed fluctuation w‘T‘ at the surfaceMittwoch, 15. Juni 2011
  33. 33. OFFSHORE WIND ENERGY METEOROLOGY VERTICAL WIND PROFILE OVER SEA Example: Ratio of wind speeds at 50m and 10m as a function of stability parameter 10/L for different estimation methods for L But how to determine L? (2) Gradient method Differences of temperature and wind speed measurements at 10m and 50m are used to calculate the gradient Richardson number RiΔ and converting it to L with virtual temperature difference ΔTv and the height z‘=(z1-z2)/ln(z1/z2)Mittwoch, 15. Juni 2011
  34. 34. OFFSHORE WIND ENERGY METEOROLOGY VERTICAL WIND PROFILE OVER SEA Example: Ratio of wind speeds at 50m and 10m as a function of stability parameter 10/L for different estimation methods for L But how to determine L? (3) Bulk method Use of air and sea surface temperature measurements and the 10m wind speed as input to approximation methodMittwoch, 15. Juni 2011
  35. 35. OFFSHORE WIND ENERGY METEOROLOGY VERTICAL WIND PROFILE OVER SEA Example: Ratio of wind speeds at 50m and 10m as a function of stability parameter 10/L for different estimation methods for L Data: Rødsand, Baltic sea, 50m, 1998-1999; solid line: MO theory unstable stable sonic method gradient method bulk method ‣ Evidence of larger deviations from MO for stable stratification (despite poor data quality :-( ) ‣ Results depend on „measurement“ of L Lange (2002)Mittwoch, 15. Juni 2011
  36. 36. OFFSHORE WIND ENERGY METEOROLOGY VERTICAL WIND PROFILE OVER SEA Example: Ratio of wind speeds at 50m and 10m as a function of stability parameter 10/L for different estimation methods for L Results show: ‣ Established theories may fail when basic assumptions are no longer valid ‣ Availability of (more) high quality measurement data is essential ‣ Results may depend on specific techniques and data for analysis (usually indicator for non-optimal solution...)Mittwoch, 15. Juni 2011
  37. 37. OFFSHORE WIND ENERGY METEOROLOGY TURBULENCE INTENSITY Measured turbulence intensity depending on wind speed in different heights and comparison with IEC 61400-3 FINO 1, January 2004 – November 2006 ‣ TI strongly depends on wind speed ‣ Influence of surface roughness decreases with height ‣ IEC standard for single turbines adequate 90-percent quantiles of measured turbulence intensity (black lines) depending on wind speed in different heights M. Türk, S. Emeis (2007) compared to turbulence intensity given by IEC 61400-3 (grey lines)Mittwoch, 15. Juni 2011
  38. 38. OFFSHORE WIND ENERGY METEOROLOGY TURBULENCE INTENSITY Measured turbulence intensity depending on wind speed in different heights and comparison with IEC 61400-3 FINO 1, January 2004 – November 2006 ‣ TI strongly depends on wind speed ‣ Influence of surface roughness decreases with height ‣ IEC standard for single turbines convective turbulence mechanical turbulence adequate 90-percent quantiles of measured turbulence intensity (black lines) depending on wind speed in different heights M. Türk, S. Emeis (2007) compared to turbulence intensity given by IEC 61400-3 (grey lines)Mittwoch, 15. Juni 2011
  39. 39. OFFSHORE WIND ENERGY METEOROLOGY APPLICATION I: CONSEQUENCES FOR MODELING OFFSHORE WIND SPEED PROFILES ‣ Vertical Offshore Wind Speed Profiles ‣ Profiles and Thermal Stratification at FINO1 ‣ 1-D Profile Models (Peña/Gryning, MO-ICWP) ‣ Offshore Performance of Meso-Scale Models thanks to Jens Tambke / ForWindMittwoch, 15. Juni 2011
  40. 40. OFFSHORE WIND ENERGY METEOROLOGY FINO1 MEASUREMENT TOWER ‣ Height: 103 m ‣ Water depth: ~30m ‣ Location: German beight, 45km north of Borkum (54° 0.86 N, 6° 35.26 E) ‣ Wind speed measurements: Cup anemometer at 8 heights (33-103m), sonic anemometer at 40/60/80m ‣ Problem: short booms error by flow around mast Corrections! FINO1Mittwoch, 15. Juni 2011
  41. 41. OFFSHORE WIND ENERGY METEOROLOGY FINO1: THERMAL STRATIFICATION Binned Wind Speed Ratios unstable stableMittwoch, 15. Juni 2011
  42. 42. OFFSHORE WIND ENERGY METEOROLOGY COMPARISON: MEAN PROFILES AT FINO1 Model Input: Wind speed time series at 33m height Observation Wind directions: z0=0.2m IEC-3 190° – 250° m WAsP Monin-ICWPMittwoch, 15. Juni 2011
  43. 43. OFFSHORE WIND ENERGY METEOROLOGY MO PROFILES AND BOUNDARY LAYER HEIGHT zi Mixing Length Approach from Peña Gryning [BLM 2008]: Unstable Neutral Stable Boundary Layer Height Rossby, Montgomery (1935)Mittwoch, 15. Juni 2011
  44. 44. OFFSHORE WIND ENERGY METEOROLOGY FINO1: THERMAL STRATIFICATION Speed Ratio (u90/u33) vs. Stability (z/L) stable unstable u(90m) 1.05 u(33m) Stability: 40m/L (Sonic@40m)Mittwoch, 15. Juni 2011
  45. 45. OFFSHORE WIND ENERGY METEOROLOGY FINO1: THERMAL STRATIFICATION Speed Ratio (u90/u33) vs. Stability (z/L) Peña/Gryning 2008 Stability: 40m/L (Sonic@40m)Mittwoch, 15. Juni 2011
  46. 46. OFFSHORE WIND ENERGY METEOROLOGY FINO1: THERMAL STRATIFICATION Speed Ratio vs. Stability (z/L) u(90m)/u (33m) u(70m)/u (33m) u(50m)/u (33m)Mittwoch, 15. Juni 2011
  47. 47. OFFSHORE WIND ENERGY METEOROLOGY FINO1: THERMAL STRATIFICATION Speed Ratio vs. Stability (z/L) u(90m)/u (33m) Peña/Gryning u(70m)/u (2008) (33m) u(50m)/u (33m)Mittwoch, 15. Juni 2011
  48. 48. OFFSHORE WIND ENERGY METEOROLOGY MESO-SCALE MODELS AT FINO1 Bias RMSE m/s m/s ECMWF -0.4 1.6 Op. Analysis FINO1, DWD -0. 1.4 alpha Op. Analysis 1 ventus MM5 -0. 2.3 with NCEP 1 (2004) MM5 -0. 1.5 with ECMWF 1 WRF -0. 1.8 with NCEP 1 (2006) Mean wind speeds at 100m: ~10m/s Mean potential power production: 50% of installed capacityMittwoch, 15. Juni 2011
  49. 49. OFFSHORE WIND ENERGY METEOROLOGY WRF: MELLOR-YAMADA-JANJIC PBL-SCHEME Mellor and Yamada [1974, 1982]; Janjic [2002]Mittwoch, 15. Juni 2011
  50. 50. OFFSHORE WIND ENERGY METEOROLOGY WRF: IMPROVED MELLOR-YAMADA PBL-SCHEME Suselj et al, BLM (2009)Mittwoch, 15. Juni 2011
  51. 51. OFFSHORE WIND ENERGY METEOROLOGY FINO1: MEAN WIND PROFILES AT 0-200m WRF DWD-LME Wind directions: 190° – 250° ObservationMittwoch, 15. Juni 2011
  52. 52. OFFSHORE WIND ENERGY METEOROLOGY FINO1: SPEED RATIO (u90/u33) vs. 10m/L Monin-Obukhov Observation WRFMittwoch, 15. Juni 2011
  53. 53. OFFSHORE WIND ENERGY METEOROLOGY MEAN WRF-PROFILES AND STABILITY unstable -0.6 10m/L stable 10m/L +0.6 -0.6 -0.3 0 +0.3 +0.6Mittwoch, 15. Juni 2011
  54. 54. OFFSHORE WIND ENERGY METEOROLOGY FINDINGS ‣ Thermal Stratification has a crucial Impact on offshore wind profiles ‣ Observed Wind Profiles show good agreement with Monin-Obukhov profiles for stabilities with 10m/L 0.12 ‣ Meso-scale Models WRF and LME (Cosmo-EU) ‣ perform very well with MYJ-Scheme ‣ capture low, stable boundary layer heightsMittwoch, 15. Juni 2011
  55. 55. OFFSHORE WIND ENERGY METEOROLOGY APPLICATION II: EU PROJECT OFFSHOREGRID Objective (WP 3.2): Time series calculation of offshore wind speed future wind power for the North and Baltic Sea ‣ Input: 6-hourly global analysis data (FNL), 100 x 100 km2 ‣ Output (WRF): 1-hourly, 9 x 9 km2 or 27 x 27 km2 ‣ Pre-processing of input data and boundary conditions ‣ Model setup, supervision of model runs, restarts and review ‣ Validation with selected available dataMittwoch, 15. Juni 2011
  56. 56. OFFSHORE WIND ENERGY METEOROLOGY WRF MODEL DOMAINS WRF setup: 2-domain, nested formulation Resolution: 1st domain: 27x27 km2 2nd domain: 9x9 km2Mittwoch, 15. Juni 2011
  57. 57. OFFSHORE WIND ENERGY METEOROLOGY EXAMPLE: WIND SPEEDS IN STORM „FRANZ“ 11 January 2007 WRF-wind speeds at 90m height (in m/s) 2007_01_11_05_00Mittwoch, 15. Juni 2011
  58. 58. OFFSHORE WIND ENERGY METEOROLOGY EXAMPLE: WIND SPEEDS IN STORM „KIRYLL“ 18 January 2007 WRF-wind speeds at 90m height (in m/s)Mittwoch, 15. Juni 2011
  59. 59. OFFSHORE WIND ENERGY METEOROLOGY ANNUAL MEAN WIND SPEEDS AT 50m 2007 averages of WRF wind speeds at 90m height (in m/s)Mittwoch, 15. Juni 2011
  60. 60. OFFSHORE WIND ENERGY METEOROLOGY ANNUAL MEAN WIND SPEEDS AT 90m 2007 averages of WRF wind speeds at 90m height (in m/s)Mittwoch, 15. Juni 2011
  61. 61. OFFSHORE WIND ENERGY METEOROLOGY MEAN WIND PROFILES AT FINO1 Wind WRF directions: 190° – 250° DWD-LME ObservationMittwoch, 15. Juni 2011
  62. 62. OFFSHORE WIND ENERGY METEOROLOGY STORMS AT FINO1 AND IN WRFMittwoch, 15. Juni 2011
  63. 63. OFFSHORE WIND ENERGY METEOROLOGY RAMPS AT FINO1 AND IN WRFMittwoch, 15. Juni 2011
  64. 64. OFFSHORE WIND ENERGY METEOROLOGY VALIDATION OF RESULTS FINO 1 WRF Parameter observation simulation Mean annual wind speed at 100m height 10.3 m/s 10.1 m/s Wind speed bias -0.2 m/s Wind speed dispersion error ~ RMSE 1.8 m/s Annually averaged potential power production of a single turbine, GH power 60.6 % 59.1 % curve (Capacity Factor) Annually averaged potential power production of a wind farm, GH power 53.4 % 52.0 % curve with wake losses (Capacity Factor) Overall power losses due to wakes 11.9 % 12.0 %Mittwoch, 15. Juni 2011
  65. 65. OFFSHORE WIND ENERGY METEOROLOGY OUTLOOK RESEARCH NEEDS (I) ‣ Measurements for optimization of micro- and meso-scale meteorological models ‣ Measurements for optimization of micro- and meso-scale meteorological models incl. satellite remote sensing (vertical structure?!) ‣ Improved wake modeling (multiple wakes, wind farm wakes, LES) ‣ Future Studies for Offshore Wind Resource Assessment: ‣ Wake Effects and Climate Impacts of Offshore Wind Farms ‣ Wakes from large wind farms ‣ Impact of Wakes on the local to regional climate: boundary layer height, low level jets, boundary layer clouds ‣ Future climates and wind resources ‣ Validate new mesoscale parameterization for offshore conditionsMittwoch, 15. Juni 2011
  66. 66. OFFSHORE WIND ENERGY METEOROLOGY OUTLOOK RESEARCH NEEDS (II) ‣ Surface waves and turbulent boundary layers and their mutual relationships: ‣ complex wave surfaces in ABL and OBL LES ‣ coupled wind-wave and wave-current models ‣ OBL and ABL mixing parameterizations with wave effects; ‣ wave and turbulence mechanics in high winds (e.g., hurricanes) ‣ wave-breaking structure and statistical distributions ‣ disequilibrium, mis-aligned wind-wave conditionsMittwoch, 15. Juni 2011
  67. 67. OFFSHORE WIND ENERGY METEOROLOGYMittwoch, 15. Juni 2011

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