As wind-turbine farms expand, research shows they could offer diminishing returns

As wind-turbine farms expand, research shows they could offer diminishing returns

Renewable wind energy is experiencing a boom, with more wind turbines popping up across landscapes in the U.S. and abroad. Indeed, wind energy accounted for 3.3 percent of electricity generation in the United States in 2011, according to the U.S. Energy Information Administration. Globally, that number was 2.9 percent for the same year.

But as wind turbines proliferate, researchers at the University of Kansas are looking at how these forests of turbines affect the wind itself. What happens to the wind when a larger number of wind turbines removes more and more of the of atmospheric motion?

Atmospheric science professors Nate Brunsell and David Mechem in KU's Department of Geography are co-authors of a new study just published in the Proceedings of the National Academy of Sciences by an international research group that evaluated the effects of large on atmospheric flow and its implications for how much renewable energy the turbines can generate.

"Wind turbines generate electricity by removing energy from the wind, so a larger number of wind turbines should result in a slowdown of the winds in the lower atmosphere," Mechem said.

The researchers quantified this phenomenon in numerical simulations by applying a sophisticated model normally used for weather forecasting to one of the windiest regions of the United States.

The team found that a slowdown effect triggered by wind turbines is substantial for large wind farms and results in proportionally less renewable energy generated for each turbine versus the energy that would be generated from an isolated wind turbine.

While the researchers stress that no current or planned wind farm approaches the size or concentration that would cause the slowdown effect, their results suggest the phenomenon tied to large wind farms needs to be accounted for in future planning of .

"When just a few are installed, each additional turbine results in a similar increase in electricity generated, as you might expect," Brunsell said.

However, when a substantial number of turbines are installed over a small area, the amount of electricity generated is no longer governed by simple multiplication, according to the researchers.

"Instead, because the turbines extract energy from the wind, additional turbines will each generate less and less electricity," Mechem said.

The team's simulations estimate this slowdown effect results in a practical upper limit of 1 megawatt per square kilometer that can be generated—far less than previous estimates not accounting for the effect. Current farms are operating well below this generation limit, but the authors found that this slowdown effect needs to be accounted for, particularly when comparing different sources of .

The study was published online in the scientific journal Proceedings of the National Academy of Sciences on Aug. 24.


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Localized wind power blowing more near homes, farms and factories

More information: Two methods for estimating limits to large-scale wind power generation, Lee M. Miller, DOI: 10.1073/pnas.1408251112
Citation: As wind-turbine farms expand, research shows they could offer diminishing returns (2015, August 31) retrieved 23 August 2019 from https://phys.org/news/2015-08-wind-turbine-farms-diminishing.html
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Aug 31, 2015
"Wind turbines generate electricity by removing energy from the wind, so a larger number of wind turbines should result in a slowdown of the winds in the lower atmosphere," Mechem said.
"Instead, because the turbines extract energy from the wind, additional turbines will each generate less and less electricity," Mechem said.
As it was predicted, a huge environmental impact when used in large-scale.
..with more wind turbines popping up across landscapes in the U.S. and abroad.
Ruining our natural landscapes, disturbing wildlife's habitats.


Aug 31, 2015
What's new here? Better quantification and more accuracy?

Smaller systems using appropriately-configured PV/wind/battery units will probably be ubiquitous in a decade for distribution, not just transmission. They are also good for villages.

The integration of local resources can often provide sufficient power for substantial gains in society and productivity.

Aug 31, 2015
Hmmmm, . . with the development of better superconductors, how soon will Magnetic Energy Storage come back? Utilities are counting on ES for the future.

A small generating unit of any kind coupled with storage can support a long radial from within the length or at the other end.

Sep 01, 2015
What's new here? Better quantification and more accuracy?


Nothing. The same 1 MW/sq-km practical limit was found by studies years ago, and promptly ignored by everyone.

Here's the link to the earlier paper: http://iopscience.../015021/

Are global wind power resource estimates overstated?

Estimates that ignore the effect of wind turbine drag on local winds have assumed that wind power production of 2–4 W m−2 can be sustained over large areas. New results from a mesoscale model suggest that wind power production is limited to about 1 W m−2


But it's good to know that there's some critical thinking in Texas as well.

Smaller systems...


...produce less energy in total. In order to cover for a significant fraction of the energy demand, we do need to put wind turbines literally everywhere, especially because of the diminishing returns.


Sep 01, 2015
Wind farms in the US are already reaching the predicted saturation size, such as the Biglow Canyon Wind Farm (100 km^2) which is making about 150 MW on average for a power density of 1.5 W/m^2 - so it's not just a theoretical concern. Wind power is already, at this small scale, being built big enough to begin limiting itself.

A counter example is Shepherds Flat Wind Farm in Oregon, which is supposed to be a 78 km^2 site with 845 MW nominal capacity and 2,000 GWh yearly output which calls for 2.9 W/m^2

The difference between the two is in how they are sited. The Shepherds Flat is split into three roughly equal parts: North, Central and South, which are separated from each other, while the Biglow site is more of a contiguous plot.

The ultimate problem of having the 1 W/m^2 limit for wind power comes with the smaller more densely populated countries such as the UK, where power use exceeds 1 W/m^2 so there's actually not enough land for wind turbines.


Sep 01, 2015
Or to make the same comparison elsewhere, the total energy demand in California should be about 0.08 W/m^2 for electricity and on the order of 0.3 - 0.4 W/m^2 for all energy divided by the area of the state.

So theoretically you only need to fill half of California with wind turbines to satisfy the demand. Trouble is, not all land area is available for use, and the efficiency of using said energy for all purposes is not 100%.

Sep 01, 2015
Trouble is, we do not have to do that, because we are more intelligent than those not in the business. We have hydro, geothermal, PV, landfill gas, pumped storage, and other sources we have been developing for decades while the rest of you polluted the landscape.

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