Wind Power and Wind Speed

I received serious skepticism to my idea that wind turbines could significantly slow the wind speed on the Great Plains. One of the criticisms came from an atmospheric scientist I asked to weigh in on the matter. The problem is, I did not find either of their arguments convincing, although I concede Daniel knows more about it than I do.

In responding to them, I came up with an approach for calculating the total power of the wind in the Great Plains. Wind is caused by differences in temperature and pressure as a result of uneven solar heating. Hence the total energy of the wind is a small fraction of the total solar flux. I’m guessing that the amount of solar flux that is actually converted into wind energy is below 1%, probably far below that, but I’ll use 1% until someone gives me a better number.

The Great Plains is 1.4 millions square miles in area, including parts in Canada and Mexico. The average solar flux is about 4 MWh/day/m2 (using numbers for Des Moines, IA.) There are 2.6 million square meters per square mile, making the total solar flux on the Great Plains about 14 trillion MWh/day. Using my 1% conversion efficiency into wind, and 24h in a day, we get total average wind power on the great Plains of 6,000 million MW. That energy is currently absorbed by objects on the ground and internal frictional losses in the air. To create significant wind speed drops, a significant fraction of that 6,000 million MW would have to be absorbed by wind turbines.

In my previous article, I used another approach to calculate that 1 million MW of wind turbines would be enough to significantly slow the wind on the Great Plains. Hence, unless my 1% solar-to-wind conversion efficiency is too high by three orders of magnitude, it looks like the skeptics were right.

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4 Comments

  1. P. Kahn said

    Wind turbines convert a portion of the kinetic energy of the atmospheric flow into electrical energy and they convert a portion into increased drag due to turbulent wakes created by the turbines. So, in the vicinity of a large deployment of turbines, there will be a local velocity deficit that can extend for a significant distance downwind of the turbines. Superimpose a series of such developments and the wind speed will be generally suppressed. The replacement of the kinetic energy lost to drag and to electrical energy extraction by the turbines is accomplished through the transfer of kinetic energy from higher levels in the atmosphere by means of turbulent frictional drag. The degree that this vertical transfer of momentum matches the increased drag caused by the wind turbines will determine how much of a local wind speed deficit will occur in the portion of the atmosphere where the turbines operate (the lowest 200 meters of the atmospheric boundary layer). On an overall energy balance, it seems clear that 1 million MW of wind energy will not have a significant impact on the kinetic energy of the entire depth of the atmosphere. But for reasons noted above, the impact very well may be locally significant.

    • Tom said

      Thanks… I appreciate having an expert weigh in.

  2. Jamie Bull said

    On a related topic, have you seen the paper by Chien Wang and Ronald Prinn at MIT which discusses warming effects from wind turbines? Their model finds local warming over land but a cooling over sea. Another nudge in the direction of offshore wind?

    There are a few issues with the analysis, not least that it ignores the cooling effect of avoided carbon emissions which I have taken a look at over on the oCo Carbon blog.

    http://ococarbon.wordpress.com/2010/05/24/could-wind-turbines-cause-more-global-warming-than-they-prevent/

  3. [...] 18, 2010 at 2:20 pm · Filed under Global Warming, Wind power, wind Jamie Bull brought to my attention a paper saying that land based wind turbines are likely to create a small degree of earth surface [...]

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