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New insights on wind turbine wakes from large-eddy simulation: Wake contraction, dual nature, and temperature effects

Impacts of maritime shipping on air pollution along the U.S. East Coast

The Jensen wind farm parameterization

Impacts of replacing coal with renewable energy sources and electrifying the transportation sector on future ozone concentrations in the U.S. under a warming climate

Comparison of individual versus ensemble wind farm parameterizations inclusive of sub-grid wakes for the WRF model

Cristina L. Archer is Professor and Unidel Howard Cosgrove Career Development Chair in the Environment, with a split appointment between the Department of Geography and Spatial Sciences and the Department of Mechanical Engineering. She is also Director of the Center for Research in Wind (CReW), formerly the Center for Carbon-free Power Integration (CCPI). Cristina is the Faculty Director of the Eco-Entrepreneurship certificate program, and her research interests include: renewable energy, wind power, meteorology, climate change, air quality, numerical modeling of atmospheric processes.

Cristina is Director of the Atmosphere and Energy Research Group (AERG) of PhD students and postdocs, and she serves on the Editorial Board of the open-access journal Meteorological Applications of the Royal Meteorological Society by Wiley. Cristina is also on the Editorial Board of the journal Bulletin of the Atmospheric Science and Technology of the Italian Association of Atmospheric Sciences and Meteorology (AISAM – Associazione Italiana di Scienze dell’Atmosfera e Meteorologia) by Springer.

Air Quality

Wind Power

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Meteorology

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University of Delaware Faculty Profile

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Wind energy conference

Scientists want to put ‘speed bumps’ in hurricane alley to slow down storms

Wind turbines could put the brakes on hurricanes

Staggered Turbines Harness the Most Wind Power

When the wind blows: New wind energy research focuses on turbine arrangement, wind seasonality

Surface roughness for offshore wind energy

The importance of transport to ozone pollution in Delaware

An assessment of compressibility effects for large wind turbines using the blade element momentum method

Professor, Geography and Spatial Sciences

Professor Cristina Archer, of the University of Delaware, speaks on “Wind energy, atmospheric turbulence, and hurricanes: How to save lives and money with wind turbine wakes” as part of the 2017/2018 Highlight Seminar Series at the Andlinger Center for Energy and the Environment at Princeton University.

The seminar took place on September 21, 2017.

ABSTRACT
Wind is already the cheapest renewable energy source and in certain cases electricity from wind is even cheaper than that from coal, natural gas, and nuclear power plants. This advantage is due in part to the fact that wind farms have been installed in the best locations, characterized by high and relatively steady winds. As the best spots eventually run out, wind farms will be installed inevitably at locations with lower and less reliable winds. How can wind power remain competitive in these less ideal conditions? Future improvements in wind turbine design and engineering are expected to improve wind turbine performance by a few percents. The most promising improvement, however, is expected to arise from smarter wind farm layouts that take into account the effects of wind turbine wakes. Understanding wind turbine wakes is therefore important to ensure future wind energy growth and competitiveness.

Results from sophisticated wake modeling simulations, called Large-Eddy Simulations, have already shown that smart array layouts can improve the performance of a wind farm by 13-33%. These smart layouts include increasing spacing between turbines along and/or across the prevailing wind direction and staggering, rather than aligning, consecutive rows of turbines.

In addition to improving wind farm performance, understanding wind turbine wakes can also bring unexpected benefits in the case of offshore wind farms. Large arrays of offshore wind turbines have been shown to provide protection from wind damage and from storm surge in coastal communities during hurricanes. This benefit, again, comes from the wind turbine wakes. Because wind turbines extract kinetic energy from the atmosphere, they lower wind speeds in their wakes. During hurricanes, these wakes can extend several kilometers downwind of a wind farm. Because winds are reduced in these wakes, wind stress on the ocean surface, which is proportional to the square of wind speed, is reduced too in the wakes. Storm surge, which is the sea level rise accompanying high-wind events and which is proportional to wind stress, is therefore dramatically reduced too. In addition, the lower winds also reduce ocean waves and surface friction, which feed into the hurricane core, weakening the hurricane. Results for hurricanes Katrina, Isaac, and Sandy show that tens to hundreds of thousands of offshore wind turbines can not only power the nation, but also reduce winds by 25-41 m/s and storm surges by 6-79%.

In conclusion, understanding wind turbine wakes is crucial to improve wind farm performance, keep wind energy economically competitive, and add protection from high-wind events in coastal communities. Wind turbine wakes can save you money and potentially save your life too!

BIO
Cristina L. Archer is an associate professor in the College of Earth, Ocean, and Environment at the University of Delaware, where she has a joint appointment between the Physical Ocean Science and Engineering program and the Department of Geography.  She received her Ph.D. in Civil and Environmental Engineering from Stanford University in 2004. She held a post-doctoral position there in 2004-2005 and then worked as an atmospheric modeler in the air quality district of San Francisco in 2005-2007. Dr. Archer joined the Carnegie Institution for Science in 2007 as a research associate. She was an assistant professor in the Department of Geological and Environmental Sciences of the California State University Chico during 2008-2011. She joined the University of Delaware in 2011. Dr. Archer’s research interests include wind power, meteorology, air quality, climate change, and numerical modeling.

Highlight Seminar: Cristina Archer, U. of Delaware

#EOLSeminarSeries

TITLE: The Complex Story of How Wind Turbines Affect Near-Ground Properties

SPEAKER: Christina Archer, Center for Research in Wind, University of Delaware

____________________________________________________________
ABSTRACT

Wind turbines generate turbulent wakes, which can potentially influence the local microclimate near the ground. The mechanism generally proposed is enhanced vertical mixing, basically an increase in mixing properties caused by the higher turbulent kinetic energy in the wake than outside of it. Whereas vertical mixing is enhanced in the wake within the rotor area, especially above hub height, evidence in the recent literature, based on wind tunnel experiments and high-resolution numerical simulations, suggests that it does not actually occur near the ground.

We conducted therefore the VERTical Enhanced miXing (VERTEX) field campaign in late summer 2016, during which we measured near-surface turbulent fluxes, wind speed, temperature, and moisture under and outside of the wake of a wind turbine located near the shore in Lewes, Delaware. We found a reduction of turbulent momentum fluxes, friction velocity, and wind speed, as well as no enhancement of sensible heat fluxes near the ground, which indicate reduced, not enhanced, vertical mixing near the ground under the wakes. We also observed a slight increase in 2-m temperature in most cases, despite unchanged surface heat fluxes. The 2-m temperature change was sensitive to the vertical temperature gradient (i.e., lapse rate)across the rotor area and to wind speed near hub height.

Based on our analysis, we propose that what controls near-surface temperature in the presence of wind turbine wakes is not heat flux per se, but rather the convergence/divergence of the heat fluxes below the wake. Because of the reduced mixing near the ground, the surface heat fluxes are slightly reduced or unchanged, but the enhanced mixing in the upper wake increases the (generally downward) heat fluxes near hub height. Convergence of the heat fluxes therefore occurs below the wake, thus warming, even during unstable conditions.

Wind farm parameterizations for mesoscale models must incorporate or resolve this convergence/divergence mechanism in their formulation and the mesoscale model must have enough vertical resolution below the wake to properly resolve it in order to predict correctly the effects of wind farms on weather and climate near the ground.

Dr. Cristina Archer - 08/04/20

Dr. Cristina Archer from the College of Earth, Ocean and Environment at the University of Delaware, Newark speaks to SoMAS on Wednesday, April 2, 2014.

TOPIC:  Wind Energy, Atmospheric Turbulence, and Hurricanes:
How to Save Lives and Money with Wind Turbine Wakes"

Abstract
 
Wind is already the cheapest renewable energy source and in certain cases electricity from wind is even cheaper than that from coal, natural gas, and nuclear power plants. This advantage is due in part to the fact that wind farms have been installed in the best locations, characterized by high and relatively steady winds. As the best spots eventually run out, wind farms will be installed inevitably at locations with lower and less reliable winds. How can wind power remain competitive in these less ideal conditions? Future improvements in wind turbine design and engineering are expected to improve wind turbine performance by a few percents. The most promising improvement, however, is expected to arise from smarter wind farm layouts that take into account the effects of wind turbine wakes. Understanding wind turbine wakes is therefore important to ensure future wind energy growth and competitiveness.
Results from sophisticated wake modeling simulations, called Large-Eddy Simulations, have already shown that smart array layouts can improve the performance of a wind farm by 13-33%. These smart layouts include increasing spacing between turbines along and/or across the prevailing wind direction and staggering, rather than aligning, consecutive rows of turbines.
In addition to improving wind farm performance, understanding wind turbine wakes can also bring unexpected benefits in the case of offshore wind farms. Large arrays of offshore wind turbines have been shown to provide protection from wind damage and from storm surge in coastal communities during hurricanes. This benefit, again, comes from the wind turbine wakes. Because wind turbines extract kinetic energy from the atmosphere, they lower wind speeds in their wakes. During hurricanes, these wakes can extend several kilometers downwind of a wind farm. Because winds are reduced in these wakes, wind stress on the ocean surface, which is proportional to the square of wind speed, is reduced too in the wakes. Storm surge, which is the sea level rise accompanying high-wind events and which is proportional to wind stress, is therefore dramatically reduced too. In addition, the lower winds also reduce ocean waves and surface friction, which feed into the hurricane core, weakening the hurricane. Results for hurricanes Katrina, Isaac, and Sandy show that tens to hundreds of thousands of offshore wind turbines can not only power the nation, but also reduce winds by 25-41 m/s and storm surges by 6-79%.
In conclusion, understanding wind turbine wakes is crucial to improve wind farm performance, keep wind energy economically competitive, and add protection from high-wind events in coastal communities. Wind turbine wakes can save you money and potentially save your life too!

SoMAS / ITPA - Wind Energy, Atmospheric Turbulence, and Hurricanes

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