Outlook - Wind Energy Meteorology: Atmospheric Physics for Wind Power Generation - page 153

7.6 Repercussions of Large-Scale Wind Power Extraction
on Weather and Climate
Large-scale exploitation of wind energy will probably have impacts on regional
winds. Large wind farms increase the surface roughness and the surface drag and
thus change the local and regional momentum budgets. This interaction has been
shown in Chap. 6 . More challenging is the investigation of global effects. If the
extracted energy comes close to the level of the totally available wind energy (see
Sects. 1.4 and 1.5 above), it will definitely have an impact on the global climate by
changing the momentum and energy budgets. Therefore, generation of renewable
energy from the wind at this level requires an assessment of the impact on the
global climate before such a large amount of wind power will be installed. Such an
assessment has to be made with complex Earth system models which are able to
simulate the non-linear interactions between the different compartments in the
Earth system, i.e. the atmosphere, the biosphere, the hydrosphere, the oceans and
the ice.
A first step to address this issue has been made by Wang and Prinn ( 2010 ). They
have performed simulations with the Community Climate Model Version 3 of the
US National Center for Atmospheric Research with a mixed layer ocean (Kiehl
et al. 1998 ) to assess the impact of onshore wind turbines producing 10 % of the
global demand in 2010 (4.5 TW or roughly 140 EJ/yr). They find surface warming
exceeding 1 C over onshore wind power installations due to lesser cooling fol-
lowing lower wind speeds within the large wind parks. Significant warming and
cooling remote from the installations, and alterations of the global distributions of
rainfall and clouds also occur. The climate impacts became negligible when the
production fell below 1 TW.
In a second study Wang and Prinn ( 2011 ) investigated the effect of offshore
wind turbines by increasing the ocean surface drag coefficient. This time they used
the Community Atmospheric Model version 3 (CAM3) of the Community Climate
System Model (CCSM), developed by the US National Center for Atmospheric
Research (NCAR) (Collins et al. 2006 ). They simulated the impact of installing a
sufficient number of wind turbines on coastal waters with depths less than 600 m
over the globe that could potentially supply up to 25 % of predicted 2100 world
energy needs (45 TW). In contrast to land installation results above (Wang and
Prinn ( 2010 ), the offshore wind turbine installations are found to cause a surface
cooling over the installed offshore regions. This cooling is due principally to the
enhanced latent heat flux from the sea surface to lower atmosphere, driven by an
increase in turbulent mixing caused by the wind turbines which was not entirely
offset by the concurrent reduction of mean wind kinetic energy. Wang and Prinn
( 2011 ) found that the perturbation of the large-scale deployment of offshore wind
turbines to the global climate is relatively small compared to the case of land-
based installations as shown in Wang and Prinn ( 2010 ).
A more severe impact of large-scale wind power generation in the order of
10 TW is that such a large extraction of kinetic energy degenerate the efficiency by