Impacts of wind farm wakes on ocean surface waves and

waves on wind resources

Jana Fischereit and Xiaoli Guo Larsen

Resource Assessment Modelling

Introduction: Offshore Environment

ATMOSPHEREFF , Ta, H, dT/dz

OCEAN

FFc, SST , S, dT/dz

SH LHMFWAVE

2 DTU Wind Energy Impacts of wind farm wakes on ocean surface waves and waves on wind resources 27.6.2019

Introduction: Offshore Environment

ATMOSPHEREFF , Ta, H, dT/dz

OCEAN

FFc, SST , S, dT/dz

SH LHMFWAVE

Wind farm wakes

2 DTU Wind Energy Impacts of wind farm wakes on ocean surface waves and waves on wind resources 27.6.2019

Introduction: Offshore Environment

ATMOSPHEREFF , Ta, H, dT/dz

OCEAN

FFc, SST , S, dT/dz

SH LHMFWAVE

Wind farm wakes

Synthetic-apeture radar (SAR) image

2 DTU Wind Energy Impacts of wind farm wakes on ocean surface waves and waves on wind resources 27.6.2019

Introduction: Research Questions

ATMOSPHEREFF , Ta, H, dT/dz

OCEAN

FFc, SST , S, dT/dz

SH LHMFWAVE

Wind farm wakes• How much do wind farms affect the wave field?

• Environmental impact assessment• Resource assessment for wave energy

• How much do waves affect the wind field?

• Resource assessment for wind energy

→ Do we have to use coupled atmosphere-wave simulation for offshoreresource predictions / forecating?

3 DTU Wind Energy Impacts of wind farm wakes on ocean surface waves and waves on wind resources 27.6.2019

Methods: Simulations

• Coupled model simulations with different complexity

→ comparison shows impact

ATM + WAVE ATM + WAVE + WAKE ATM + WAKE

• for the German Bight area

→ relatively high density of wind farms (= Interfarm wakes relevant)

• as nested forced simulations with reanalysis data

→ to validate model performance against measurements

4 DTU Wind Energy Impacts of wind farm wakes on ocean surface waves and waves on wind resources 27.6.2019

Methods: Simulations

• Coupled model simulations with different complexity

→ comparison shows impact

ATM + WAVE ATM + WAVE + WAKE ATM + WAKE

Wake impact Wave impact

• for the German Bight area

→ relatively high density of wind farms (= Interfarm wakes relevant)

• as nested forced simulations with reanalysis data

→ to validate model performance against measurements

4 DTU Wind Energy Impacts of wind farm wakes on ocean surface waves and waves on wind resources 27.6.2019

Methods: Simulations

• Coupled model simulations with different complexity→ comparison shows impact

• for the German Bight area→ relatively high density of wind farms (= Interfarm wakes relevant)

• as nested forced simulations with reanalysis data→ to validate model performance against measurements

4 DTU Wind Energy Impacts of wind farm wakes on ocean surface waves and waves on wind resources 27.6.2019

Methods: Simulations

• Coupled model simulations with different complexity→ comparison shows impact

• for the German Bight area→ relatively high density of wind farms (= Interfarm wakes relevant)

• as nested forced simulations with reanalysis data→ to validate model performance against measurements

• 3 domains: ∆x=18 km, ∆x=6 km, ∆x=2 km

• Reanalysis: CFSR, OISST4

• COAWSTv3.2 (Warner et al., 2010): WRFv3.7 +SWAN v41.01AB with

• WBLM (Du et al., 2019)• EWP (Volker et al., 2015)

4 DTU Wind Energy Impacts of wind farm wakes on ocean surface waves and waves on wind resources 27.6.2019

Case studies for 2 selected days

2017-05-11 to 13Pronounced wakes

2016-12-23 to 25:Storm

5 DTU Wind Energy Impacts of wind farm wakes on ocean surface waves and waves on wind resources 27.6.2019

Simulation resuls and validation: SAR image

2017-05-11 17:17 2015-12-23 17:17

6 DTU Wind Energy Impacts of wind farm wakes on ocean surface waves and waves on wind resources 27.6.2019

Simulation results: wind farm wakes in 10 m and waves

(FF10,wake − FF10)/FF10 (Hm0,wake −Hm0)/Hm0

7 DTU Wind Energy Impacts of wind farm wakes on ocean surface waves and waves on wind resources 27.6.2019

Validation: Measurements

8 DTU Wind Energy Impacts of wind farm wakes on ocean surface waves and waves on wind resources 27.6.2019

Validation: Example Significant wave height (2017-05-10)

Dotted lines: Model simulationSolid lines: Observations9 DTU Wind Energy Impacts of wind farm wakes on ocean surface waves and waves on wind resources 27.6.2019

Validation: Summary

2017-05-10: Pronounced wakes

hm0 [m] FF [m/s] DD [◦] T [K]RMSE 0.26 1.57 19.66 1.3BIAS -0.21 0.12 13.62 -0.64MAE 0.22 1.32 16.09 1.07Corr 0.81 0.77 0.87 0.94

2016-12-23: Storm

hm0 [m] FF [m/s] DD T [K]RMSE 0.92 2.17 11.49 0.86BIAS -0.81 -0.68 5.64 -0.15MAE 0.83 1.92 9.53 0.69Corr 0.86 0.77 0.94 0.61

10 DTU Wind Energy Impacts of wind farm wakes on ocean surface waves and waves on wind resources 27.6.2019

Simulation results: wind farm wakes on waves

11 DTU Wind Energy Impacts of wind farm wakes on ocean surface waves and waves on wind resources 27.6.2019

Simulation results: wind farm wakes on waves

For every point in time:

Nj∑j

Ni∑i

{(Hm0,wake −Hm0)/Hm0 < x[%]

}·∆x∆y

11 DTU Wind Energy Impacts of wind farm wakes on ocean surface waves and waves on wind resources 27.6.2019

Windfarm wakes on waves and 10 m wind

Nj∑j

Ni∑i

{(Hm0,wake −Hm0)/Hm0 < x[%]

}·∆x∆y

12 DTU Wind Energy Impacts of wind farm wakes on ocean surface waves and waves on wind resources 27.6.2019

Windfarm wakes on waves and 10 m wind

Pronounced Wakes Storm

12 DTU Wind Energy Impacts of wind farm wakes on ocean surface waves and waves on wind resources 27.6.2019

Windfarm wakes on waves and 10 m wind

Pronounced Wakes Storm

12 DTU Wind Energy Impacts of wind farm wakes on ocean surface waves and waves on wind resources 27.6.2019

Ocean waves on wind resources: hub height (105 m)

13 DTU Wind Energy Impacts of wind farm wakes on ocean surface waves and waves on wind resources 27.6.2019

Ocean waves on wind resources: hub height (105 m)

after 5hours

17:20(SAR

image)

2017 2016

13 DTU Wind Energy Impacts of wind farm wakes on ocean surface waves and waves on wind resources 27.6.2019

Ocean waves on wind resources: hub height (105 m)

after 5hours

17:20(SAR

image)

2017 2016

13 DTU Wind Energy Impacts of wind farm wakes on ocean surface waves and waves on wind resources 27.6.2019

Impact of ocean waves on wind resources

Pronounced wakes (2017) Storm (2016)

14 DTU Wind Energy Impacts of wind farm wakes on ocean surface waves and waves on wind resources 27.6.2019

Conclusion and Outlook

• How much do wind farms affect the wave field?

→ decrease can be > 20 % in FF10/hm0 + affectedarea is large

• How much do waves affect the wind field?

→ On average small effects, but variable up toabout 5 % difference in FF in hub height

→ Do we have to use coupled atmosphere-wavesimulation for offshore resource predictions /forecasting?

→ From 2 case studies: impact under light winds

Further steps• Climatologically representable results: statistical downscaling

• Impact on power production, wake parameterisation, other meteorologcicalparameters

15 DTU Wind Energy Impacts of wind farm wakes on ocean surface waves and waves on wind resources 27.6.2019

References and Ackknowledgements

Du J., Bolanos R., Larsen X. G., and Kelly M. (2019): Wave boundary layer model inSWAN revisited. Ocean Science, volume 15(2):pages 361–377.http://dx.doi.org/10.5194/os-15-361-2019.

Volker P. J. H., Badger J., Hahmann A. N., and Ott S. (2015): The Explicit WakeParametrisation V1.0: a wind farm parametrisation in the mesoscale model WRF.Geoscientific Model Development, volume 8(11):pages 3715–3731.http://dx.doi.org/10.5194/gmd-8-3715-2015.

Warner J. C., Armstrong B., He R., and Zambon J. B. (2010): Development of aCoupled Ocean–Atmosphere–Wave–Sediment Transport (COAWST) ModelingSystem. Ocean Modelling, volume 35(3):pages 230 – 244. ISSN 1463-5003.http://dx.doi.org/https://doi.org/10.1016/j.ocemod.2010.07.010.

This study is mainly supported by the Danish EUDP/ForskEL project OffshoreWake(64017-0017/12521). Validation data and reanalysis data has been used from

• Deutscher Wetterdienst (German Weather Service), Climate Data Center(CDC)• FINO Datenbank (Bundesamt fur Seeschfifffahrt und Hydrographie)• EMODnet Physics system http://www.emodnet-physics.eu/Map/

• CFSR data from http://rda.ucar.edu/datasets16 DTU Wind Energy Impacts of wind farm wakes on ocean surface waves and waves on wind resources 27.6.2019