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Does extracting power from the wind change the climate?

Will installing large numbers of wind turbines have an impact on the environment – not just visual intrusion, but actual measurable effects on the atmosphere and climate? After all if you are taking many giga watts of power out won’t that slow the winds down? And have other effects?

Well the first thing to realise is that wind turbines only extract very small amounts of the energy in the wind front – which after all can be a mass of air hundreds of miles wide and several miles high. That said there can be local wind shadow effects. Indeed in medieval times there were regular disputes about blocking wind access to corn grinding windmills. But in macro terms the extraction issue would seem to be negligible.

What about more subtle impacts? In a paper in Atmos. Chem. Phys. 10 2053–2061, 2010, entitled “Potential climatic impacts and reliability of very large-scale wind farms” C. Wang and R. G. Prinn from the Center for Global Change Science and Joint Program of the Science and Policy of Global Change, Massachusetts Institute of Technology, argue that the widespread use of wind energy could lead to temperature changes. They used a three-dimensional climate model to simulate the potential climate effects associated with installation of wind-powered generators over vast areas of land or coastal ocean. They claim that ‘Using wind turbines to meet 10% or more of global energy demand in 2100, could cause surface warming exceeding 1 °C over land installations. In contrast, surface cooling exceeding 1 °C is computed over ocean installations,’ but they add ’ the validity of simulating the impacts of wind turbines by simply increasing the ocean surface drag needs further study’.

They go on ‘Significant warming or cooling remote from both the land and ocean installations, and alterations of the global distributions of rainfall and clouds also occur,’ and explain that ‘these results are influenced by the competing effects of increases in roughness and decreases in wind speed on near-surface turbulent heat fluxes, the differing nature of land and ocean surface friction, and the dimensions of the installations parallel and perpendicular to the prevailing winds’. They also say: ‘These results are also dependent on the accuracy of the model used, and the realism of the methods applied to simulate wind turbines. Additional theory and new field observations will be required for their ultimate validation.’

www.atmos-chem-phys.net/10/2053/2010/acp-10-2053-2010.html

Well yes, they do seem to have adopted a rather simplified ‘top down’ model – assuming increased drag from increased surface roughness averaged out over entire coarse-resolved grid cells, rather than looking at the impacts of individual wind turbines. An earlier ‘bottom up’ study ‘Investigating the Effect of Large Wind Farms on Energy in the Atmosphere’, in Energies 2009, 2, 816-838 by Magdalena R.V. Sta. Maria and Mark Z. Jacobson of the Atmosphere/Energy Program, Civil and Environmental Engineering Department, Stanford University, used Blade Element Momentum theory, to calculates forces on individual turbine blades. It claimed that ‘Should wind supply the world’s energy needs, this parameterization estimates energy loss in the lowest 1 km of the atmosphere to be ~0.007%’, which it said was ‘an order of magnitude smaller than atmospheric energy loss from aerosol pollution and urbanization, and orders of magnitude less than the energy added to the atmosphere from doubling CO₂.’

It added that, although there may be small moisture content changes and other minor effects, ‘the net heat added to the environment due to wind dissipation is much less than that added by thermal plants that the turbines displace’.

www.mdpi.com/1996-1073/2/4/816/pdf

Pretty clearly then we have a disagreement: especially given that Wang and Prinn say ‘1 degree from a 10% wind contribution’: would that means 10 degrees for the 100% total energy contribution looked at by Maria and Jacobson?

Underlying this conflict are pro and anti wind postures, with Maria and Jacobson obviously very much in favour, while Wang and Prinn’s paper adds in for good measure some familiar negative comments about the intermittency of wind power and the need for backup generation capacity, very long distance power transmission lines, and onsite energy storage.

Wind power does have its problems, but they seem to scraping the bottom of the barrel by trying to talk up miniscule temperature effects.

Posted by Dave Elliott on April 10, 2010 1:41 PM | Permalink