Gone with the wind – why the fast jet stream winds cannot contribute much renewable energy after all

[OKIsItJustMe]

http://www.alphagalileo.org/ViewItem.aspx?ItemId=115011&CultureCode=en

Gone with the wind – why the fast jet stream winds cannot contribute much renewable energy after all

30 November 2011 Max Planck Institute for Biogeochemistry

The assumption that high jet steam wind speeds in the upper atmosphere correspond to high wind power has now been challenged by researchers of the Max Planck Institute for Biogeochemistry in Jena, Germany. Taking into account that the high wind speeds result from the near absence of friction and not from a strong power source, Axel Kleidon and colleagues found that the maximum extractable energy from jet streams is approximately 200 times less than reported previously. Moreover, climate model simulations show that energy extraction by wind turbines from jet streams alters their flow, and this would profoundly impact the entire climate system of the planet.

Jet streams are regions of continuous wind speeds greater than 25 m/s that occur at altitudes of 7-16 km. Their high speeds seem to suggest an almost unlimited source of renewable energy that would only need airborne wind energy technology to utilize it. Claims that this potential energy source could “continuously power all civilization” sparked large investments into exploitation of this potential energy resource. However, just like any other wind and weather system on Earth, jet streams are ultimately caused by the fact that the equatorial regions are heated more strongly by the sun than are polar regions. This difference in heating results in large differences in temperature and air pressure between the equator and the poles, which are the driving forces that set the atmosphere into motion and create wind. It is this differential heating that sets the upper limit on how much wind can be generated and how much of this could potentially be used as a renewable energy resource.

It is well known in meteorology that the high wind speeds of jet streams result from the near absence of friction. In technical terms, this fact is referred to in meteorology as “geostrophic flow”. This flow is governed by an accelerating force caused by pressure differences in the upper atmosphere, and the so-called Coriolis force arising from the Earth’s rotation. Because the geostrophic flow takes place in the upper atmosphere, far removed from the influence of the surface and at low air density, the slow-down by friction plays a very minor role. Hence, it takes only very little power to accelerate and sustain jet streams. “It is this low energy generation rate that ultimately limits the potential use of jet streams as a renewable energy resource”, says Dr. Axel Kleidon, head of the independent Max Planck Research Group ‘Biospheric Theory and Modelling’. Using this approach based on atmospheric energetics, Kleidon’s group used climate model simulations to calculate the maximum rate at which wind energy can be extracted from the global atmosphere. Their estimate of a maximum of 7.5 TW (1 TW = 10^12 W, a measure for power and energy consumption) is 200-times less than previously reported and could potentially account for merely about half of the global human energy demand of 17 TW in 2010.

Max Planck researchers also estimated the climatic consequences that would arise if jet stream wind power would be used as a renewable energy resource. As any wind turbine must add some drag to the flow to extract the energy of the wind and convert it into electricity, the balance of forces of the jet stream must also change as soon as energy is extracted. If 7.5 TW were extracted from jet streams as a renewable energy source, this would alter the natural balance of forces that shape the jet streams to such an extent that the driving atmospheric pressure gradient between the equator and the poles is depleted. “Such a disruption of jet stream flow would slow down the entire climate system. The atmosphere would generate 40 times less wind energy than what we would gain from the wind turbines”, explains Lee Miller, first author of the study. “This results in drastic changes in temperature and weather”.

http://dx.doi.org/10.5194/esd-2-201-2011

[FiveGoodMen]

1. "continuous wind speeds greater than 25 m/s"

If m/s means miles per second, then we're talking about 25*3600 = 90,000 miles per hour.

Not hardly!

Ah, now that I think of it... Meters per second.

Much better.

[mike_c]

4. on jupiter....

:rofl:

[mike_c]

2. this was pretty much a no-brainer....

Any scheme to extract significant amounts of energy from any surface flux (including the atmosphere and the ocean) will ultimately affect the distribution of energy and the ecosystem, marine, and aquatic processes that energy normally drives. If the energy density is high enough we can probably extract small amounts without creating significant disruption, e.g. tidal electricity generation, or extraction of relatively small amounts of wind power, but every joule that is diverted to human use is a joule that is no longer available to power other ecosystem processes.

[OneTenthofOnePercent]

3. I've always wondered what the consequence for terrestrial wind energy would be...

There is no free lunch... especially when converting one kind of energy to another.

Like you said, every joule of energy we take out of the ground-level winds is energy not available to drive the ecosystems that have existed for milleniums. What will be the effect of this, especially as the world shifts more to green energy solutions like wind?

Earth doesn't have an energy problem... it has a human population problem.

[kristopher]

5. What is the difference between a wind turbine and a tree as far as wind drag goes?

[OKIsItJustMe]

6. Well, for one thing, the tallest wind turbines are taller than the tallest trees

http://en.wikipedia.org/wiki/Sequoiadendron#Tallest

…

Tallest

Unnamed Tree - Redwood Mountain Grove - 311 feet (95 m)

…

http://en.wikipedia.org/wiki/Wind_turbine#Tallest

…

Tallest

The tallest wind turbine is Fuhrländer Wind Turbine Laasow. Its axis is 160 meters above ground and its rotor tips can reach a height of 205 meters. It is the only wind turbine in the world taller than 200 meters.

…

[kristopher]

9. Yes, and what is the difference in terms of the effects on wind drag?

That was (and is) the question.

[OKIsItJustMe]

15. Impacts of wind farms on surface air temperatures

http://dx.doi.org/10.1073/pnas.1000493107

Impacts of wind farms on surface air temperatures

Somnath Baidya Roy1 and
Justin J. Traiteur

+ Author Affiliations

Department of Atmospheric Sciences, University of Illinois, 105 South Gregory Street, Urbana, IL 61820

Edited* by Stephen H. Schneider, Stanford University, Stanford, CA, and approved August 13, 2010 (received for review January 15, 2010)

Abstract

Utility-scale large wind farms are rapidly growing in size and numbers all over the world. Data from a meteorological field campaign show that such wind farms can significantly affect near-surface air temperatures. These effects result from enhanced vertical mixing due to turbulence generated by wind turbine rotors. The impacts of wind farms on local weather can be minimized by changing rotor design or by siting wind farms in regions with high natural turbulence. Using a 25-y-long climate dataset, we identified such regions in the world. Many of these regions, such as the Midwest and Great Plains in the United States, are also rich in wind resources, making them ideal candidates for low-impact wind farms.

Wind power is one of the fastest growing energy sources in the world. Most of this growth is in the industrial sector based on large utility-scale wind farms (1). Recent studies have investigated the possible impacts of such wind farms on global and local weather and climate. Although debates exist regarding the global-scale effects of wind farms (2–5), modeling studies agree that wind farms can significantly affect local-scale meteorology (6, 7). However, these studies are based only on model simulations and are not validated against observational evidence. In this paper, we used field data and numerical experiments with a regional climate model to answer the following critical questions arising from the prior studies:

1. Does observational evidence show that wind farms affect near-surface air temperatures?


2. Can atmospheric models replicate the observed patterns of near-surface air temperatures within wind farms?


3. How can these impacts be minimized to ensure long-term sustainability of wind power?

Observed Impacts of Wind Farms

Although observed data on wind speed and turbulence in and around operational wind farms are readily available, information on other meteorological variables do not exist in the public domain. The only available information is temperature data from a wind farm at San Gorgonio, California, collected during June 18–August 9, 1989 (Fig. 1). To the best of our knowledge, this is the only meteorological field campaign conducted in an operational wind farm. The wind farm consisted of 23-m-tall turbines with 8.5-m-long rotor blades arranged in 41 rows that were spaced 120 m apart.

Data from the field campaign show that near-surface air temperatures downwind of the wind farm are higher than upwind regions during night and early morning hours, whereas the reverse holds true for the rest of the day (Fig. 2A). Thus, this wind farm has a warming effect during the night and a cooling effect during the day. The observed temperature signal is statistically significant for most of the day according to the results of a Mann–Whitney Rank Sum Test (Table 1).

…

[mike_c]

7. nothing, really, and building wind turbines is the energetic equivalent...

...of planting more trees, at least in terms of affecting atmospheric energy flux (and that's where the equivalency ends, obviously). But recall that surface winds have considerably higher energy density that high altitude winds, despite being much slower, so the amount of energy that a few trees or wind turbines extracts is not sufficient to really change the resulting fluxes. But if you extracted, say 50% of the available energy, or more-- something that would have to be done if jet streams were to be tapped for significant amounts of energy yield-- the movement of air at the surface, along with the distribution of moisture, potential evapotransporation, and probably even surface primary productivity might be significantly impacted.

Tidal generation is an even better example because the energy density is so great-- extracting a SMALL portion of that vast energy would have little ecosystem impact, but if you extracted ALL of it, the result would be similar to building tide gates and closing them, shutting off the tidal flow into and out of estuaries. That would have major ecological impact. Harvesting half the energy density would have some intermediate impact, and so on.

[kristopher]

10. Except that previous studies all look at the winds in terms of energy density.

Read this 2009 study yourself
Global Assessment of High-Altitude Wind Power Cristina L. Archer 1,* and Ken Caldeira 2
http://www.mdpi.com/1996-1073/2/2/307/pdf

[mike_c]

12. thanks, reading it now but it appears the problem shows up early...

...in the introduction. Archer and Caldeira assume that high altitude winds have high energy density: "The total wind energy in the jet streams is roughly 100 times the global energy demand <3>" This latest study from Max Planck Institute seems to contradict that, suggesting that their high velocities result not from high energy density, but simply from lack of resistance. Capturing significant proportions of that energy is much more likely to disrupt the climate drivers those jet streams provide.

[kristopher]

17. They aren't assuming.

ETA: Yes the Planck study is a contradiction, and it is good to get it out where it can be looked at. But the energy density is a function of wind speed and density and has been measured.

[Nederland]

25. Agreed

The conclusion of the OP study is not that jet stream winds do not have high energy densities--they obviously do. The point is that they achieved those energy densities due to lack of friction, not due to a stronger source.

[kristopher]

26. Not exactly...

You've slipped in a double negative, so let's rephrase for clarity:
From: "The conclusion of the OP study is not that jet stream winds do not have high energy densities--they obviously do."
To: "The study starts from the known high energy density of the jet streams."

Right.

Then you say that the winds achieved those energy densities due to lack of friction, not due to stronger force.

That can't be stated because they did not look at the way extraction would affect the input of wind generating energy into the jet stream system. They essentially took a steady state situation, changed one variable and looked at the downstream effects - without considering the upstream consequences at all. The conclusions, while interesting, have no predictive validity at all, a point Miller etal are very clear about themselves.

I'd recommend reading the reviewers comments in post 24
http://www.democraticunderground.com/discuss/duboard.php?az=show_mesg&forum=115&topic_id=318710&mesg_id=318800

[OKIsItJustMe]

11. Weather response to a large wind turbine array

http://www.atmos-chem-phys.org/10/769/2010/acp-10-769-2010.pdf

Atmos. Chem. Phys., 10, 769–775, 2010
www.atmos-chem-phys.net/10/769/2010/
© Author(s) 2010. This work is distributed under
the Creative Commons Attribution 3.0 License.

Weather response to a large wind turbine array

D. B. Barrie and D. B. Kirk-Davidoff
University of Maryland Department of Atmospheric and Oceanic Science, College Park, MD, USA

Received: 8 December 2008 – Published in Atmos. Chem. Phys. Discuss.: 29 January 2009
Revised: 8 January 2010 – Accepted: 15 January 2010 – Published: 26 January 2010

Abstract. Electrical generation by wind turbines is increasing rapidly, and has been projected to satisfy 15% of world electric demand by 2030. The extensive installation of wind farms would alter surface roughness and significantly impact the atmospheric circulation due to the additional surface roughness forcing. This forcing could be changed deliberately by adjusting the attitude of the turbine blades with respect to the wind, which would enable the “management” of a large array of wind turbines. Using a General Circulation Model (GCM), we represent a continent-scale wind farm as a distributed array of surface roughness elements. Here we show that initial disturbances caused by a step change in roughness grow within four and a half days such that the flow is altered at synoptic scales. The growth rate of the induced perturbations is largest in regions of high atmospheric instability. For a roughness change imposed over North America, the induced perturbations involve substantial changes in the track and development of cyclones over the North Atlantic, and the magnitude of the perturbations rises above the level of forecast uncertainty.

…

2.2 Size of the wind farm

The wind farm simulated in this study occupies 23% of the North American land area and is positioned in the central United States and south central Canada. Figure 1 shows the extent of the wind farm, as indicated by the rectangular box.

…

In early tests of the modeling studies described in this paper, it was found that a substantially smaller wind farm, with an area one quarter the size of the wind farm described in this paper, did not cause a large downstream impact. The perturbation induced by the smaller wind farm’s drag had a much weaker impact on upper level winds, leading to a lack of noticeable downstream effects. On the other hand, the scale of the wind farm described throughout this paper is larger than the area of surface damping that elicited a maximum downstream response in the shallow water model used by Kirk-Davidoff and Keith (2008). We expect that a modest change in the size of the wind farm studied here would have little effect on the magnitude of the downstream response. Ongoing work will characterize scale dependence in more detail.

…

4 Conclusions

Wind farms as large as those studied in the paper do not yet exist, and as such, we view this work as a theoretical problem with the potential for real world applications in the coming decades. The study presented here depicts a strong downstream impact caused by a large surface roughness perturbation in a GCM. We have assumed that the active control of turbine orientation could produce a time-dependent change in surface roughness. Atmospheric anomalies initially develop at the wind farm site due to a slowing of the obstructed wind. The anomalies propagate downstream as a variety of baroclinic and barotropic modes, and grow quickly when they reach the North Atlantic. These responses occur within a short forecast timeframe, which suggests that predictable influences on weather may be possible. This study utilized an array of highly variable initial conditions to initialize the model. Ongoing work will catalog the initial meteorological conditions necessary to generate predictable and controlled downstream effects caused by wind farms. We performed an ensemble study of one particular case with randomized initial conditions chosen for both the wind farm and the wind farm absent cases that showed that the atmospheric perturbation persists across the ensemble members. We will continue to study the wind farm effects in an ensemble context to determine the conditions necessary for induced perturbations to project strongly onto the fastest modes of error growth. This will illustrate the statistical significance and regularity of downstream changes in the atmosphere. There are open questions regarding the importance of the size of the wind farm, the sensitivity of the impacts to the value of surface roughness, the amount of time that the wind farm would have to be turned off, and the location of the wind farm with respect to overlying atmospheric structures such as the jet stream. We are continuing this work by studying these issues in greater detail.

…

[mike_c]

13. nice study....

I was wondering whether anyone had modeled the effects of increased surface drag at continental scales. I don't get into that literature often enough!

[kristopher]

16. Then you'll probably appreciate this one also

Energies 2009, 2, 816-838; doi:10.3390/en20400816
OPEN ACCESS
energies
ISSN 1996-1073
www.mdpi.com/journal/energies

ARTICLE
Investigating the Effect of Large Wind Farms on Energy in the Atmosphere
Magdalena R.V. Sta. Maria * and Mark Z. Jacobson
http://www.mdpi.com/1996-1073/2/4/816/pdf

[mike_c]

19. thank you again....

Taking a cursory look at the abstract, it suggests energy loss of 0.007% from low altitude circulation if wind energy were exploited sufficiently to provide all the world's energy needs circa 2009. That's pretty remarkable, even if it only holds to that order of magnitude! I'll ad this one to the afternoon's reading queue.

Compare that to Jeffery Dukes estimate of the "photosynthesis deficit" of burning fossil fuels, i.e. 44 * 10^18 g C yr^-1, or >400 times modern NPP across the entire planet. Again, even if that estimate is only correct to within a couple orders of magnitude, why in the hell are we talking about oxidizing biomass for energy? (Dukes 2003, Burning buried sunshine: Human consumption of ancient solar energy. Climatic Change 61: 31-44)

[kristopher]

14. And???

Are you going into another fugue where you post an endless series of irrelevant references with no reasoned explanations of the significance that only you seem to see?

[OKIsItJustMe]

18. What’s the point?

You’ve already http://en.wikipedia.org/wiki/Poisoning_the_well">poisoned the well.

[Yo_Mama]

20. There are no trees in the jetstream.

In terms of near-surface winds, the difference would be experienced in albedo effects and ground temps, also potential evap.

Land use is responsible for significant local effects. Irrigate and you raise average temps a couple of degrees in an arid climate, for example.

But how many wind turbines are out there? You have to have a very significant coverage before you see much effect.

[kristopher]

21. No one said there was.

The post that comment is in response to wrote:
"Like you said, every joule of energy we take out of the ground-level winds is energy not available to drive the ecosystems that have existed for milleniums. What will be the effect of this, especially as the world shifts more to green energy solutions like wind?"

To date we've installed 225Gw of wind turbines, most of them 1 to 1.5MW. The size will rise as we move offshore, but for now that range makes up most of the capacity. That means a lower boundary of 150,00 turbines and an upper boundary of more than 225,000 counting those smaller than 1MW that are still online.

Following paper available for download here: http://www.mdpi.com/1996-1073/2/4/816/pdf

Energies 2009, 2, 816-838; doi:10.3390/en20400816
Investigating the Effect of Large Wind Farms on Energy in the Atmosphere
Magdalena R.V. Sta. Maria * and Mark Z. Jacobson
Abstract: This study presents a parameterization of the interaction between wind turbines and the atmosphere and estimates the global and regional atmospheric energy losses due to such interactions. The parameterization is based on the Blade Element Momentum theory, which calculates forces on turbine blades. 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%. This is 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. Also, the net heat added to the environment due to wind dissipation is much less than that added by thermal plants that the turbines displace.

Abstract by sentence
This study presents a parameterization of the interaction between wind turbines and the atmosphere and estimates the global and regional atmospheric energy losses due to such interactions.

The parameterization is based on the Blade Element Momentum theory, which calculates forces on turbine blades.

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%.

This is 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.

Also, the net heat added to the environment due to wind dissipation is much less than that added by thermal plants that the turbines displace.



From the body of the analysis, pg 828:

Two scenarios needing large installations of wind farms are examined—scenario A, which assumes that wind energy displaces the CO2 from all fossil fuel energy sources (both electric and non-electric), and scenario B, which assumes that all onroad vehicles are replaced by wind-powered battery electric vehicles. For scenario A, two cases were analyzed. The first case assumes that wind displaces all fossil fuel energy worldwide that produces carbon. The second case assumes that wind displaces all fossil fuel carbon in the United States. Scenario B also examines two cases: replacing onroad vehicles throughout the whole U.S. and replacing onroad vehicles in California. California is of interest because it is the U.S. state with the largest vehicle density. Table 2 summarizes the cases. The energy losses from all these cases are examined both as the loss from the lower 1 km of the atmosphere (heretofore referred to as L1)—over global land and oceans—and the loss from only sections of the L1 layer that are above the land area of interest, e.g., over U.S. land.

scenario A, which assumes that wind energy displaces the CO2 from all fossil fuel energy sources (both electric and non-electric),
scenario B, which assumes that all onroad vehicles are replaced by wind-powered battery electric vehicles.

scenario A1 - wind displaces all fossil fuel energy worldwide that produces carbon.
scenario A2 - wind displaces all fossil fuel carbon in the United States.
scenario B1 - replace onroad vehicles in U.S.
scenario B2 - replace onroad vehicles in California.

"The energy losses from all these cases are examined both as the loss from the lower 1 km of the atmosphere (heretofore referred to as L1)—over global land and oceans—and the loss from only sections of the L1 layer that are above the land area of interest, e.g., over U.S. land."

The study used average wind speeds of 7, 8, 9, and 10 meters per second to determine power output from 1.5MW turbine operational profile and determined how many turbines would be required to achieve goal. For scenario A1:
7mps = 10 million
8mps = 8 million
9mps = 6.7 million
10mps = 5.7 million


You'll find the results on in easy to read tabular form on page 830, but here is the text:

Figure 11 shows the results of this energy analysis for Scenario A1. The different bars indicate the losses given different mean wind speeds. Larger relative energy losses are found at lower mean wind speeds, where more turbines are required to generate the same energy. Relative energy losses in L1 above global land range from 0.06%–0.08%, and those above global land plus ocean range from 0.006%–0.008%. The relative energy losses for Scenario A2 are shown in Figure 12. In this scenario, L1 above the U.S. loses 0.19%–0.23% of its energy, but when seen in the context of the global (land plus ocean) L1 layer, only 0.0012%–0.0014% is lost. Figure 13 and Figure 14 present the relative energy losses from Scenario B1 and B2, respectively. In these two cases, there is even less of an effect, even in the local L1. If all U.S. onroad vehicles were powered by wind farms, the loss in L1 over U.S. land ranges from 0.04%–0.05%. If only California vehicles, the energy loss from L1 layer over California would be 0.10%–0.12%. In L1 over global land plus ocean, a relative energy loss of 0.00026%–0.00031% results from Scenario B1, and 0.000026%–0.000032% from Scenario B2.

for scenario A1:
Larger relative energy losses are found at lower mean wind speeds, where more turbines are required to generate the same energy. Relative energy losses in L1 above global land range from 0.06%–0.08%, and those above global land plus ocean range from 0.006%–0.008%.

Hope that helps bring clarity to the matter.

[Yo_Mama]

22. Yes, it does. The whole thread is good - really good

The point I was trying to make is that tapping the jetstream would logically have a much greater effect than near-surface turbines because it is far more isolated from the biosphere than land or sea wind turbines.

If you are worried about ecological effects (I'm not saying that it is an utterly silly worry in the abstract), then avoid the "pristine" areas. While I will concede that theoretically we could alter the climate in negative ways through the use of wind turbines, for all practical intents and purposes, we are so far from that zone that the argument remains an abstraction.

That may well not be true for the jetstream, but then we aren't plopping wind turbines up there either. The only real purpose to the argument is to point out that there are practical limits to everything, and to rebut the various studies that pop up now and then claiming that wind contains huge massive amounts of energy far above what the entire planet ever needs. But since we are not trying to generate six more times the energy the planet requires, those studies too remain at the abstract level.

The more practical question is whether anything we are doing or are likely to do with wind in the next couple of decades is going to affect the biosphere more than what we are currently doing. I think one flight over Manhattan can answer that question. The change in wind patterns that our cities produce is vastly more than we can possibly induce with a 20 year wind turbine program. I defy anyone to show me a wind farm that will change albedo the way a city does, or produce vast heat columns, etc.

[OKIsItJustMe]

23. Has it occurred to you that this study is working with a global average?

Ever hear the one about the statistician who drowned in a lake with an average depth of 6 inches?

Global warming at this point is not too bad, on a global average, but the local change in the Arctic is punishing.

This study measures a significant local effect in the wake of an array of wind turbines:
http://www.democraticunderground.com/discuss/duboard.php?az=show_mesg&forum=115&topic_id=318710&mesg_id=318732

This study suggests a larger effect from larger arrays:
http://www.democraticunderground.com/discuss/duboard.php?az=show_mesg&forum=115&topic_id=318710&mesg_id=318727

These do not mean that the average global temperature will be radically affected.


How are turbines different from trees?

• Is anyone planting mutant extra-giant sequoias on the “great plains?”
• Do trees grow to maximize their ability to catch the wind? (Trees tend to grow in masses, called forests, sheltering each other from the wind. What would their effect be if they were planted sparsely like wind turbines?)

How are wind turbines different from trees? Which trees spin over and over in the wind?

http://dx.doi.org/10.1073/pnas.1000493107

…

A possible explanation for this phenomenon can be drawn from the hypothesis proposed by Baidya Roy et al. that turbulence generated in the wake of the rotors enhance vertical mixing (6). In a stable atmosphere when the lapse rate is positive, i.e., a warm layer overlies a cool layer, enhanced vertical mixing mixes warm air down and cold air up, leading to a warming near the surface. In an unstable atmosphere with negative lapse rate, i.e., cool air lying over warmer air, turbulent wakes mix cool air down and warm air up, producing a cooling near the surface. Vertical profiles of temperatures from the Edwards Air Force Base corroborate this hypothesis. This base is the World Meteorological Organization (WMO) recognized weather station nearest to the San Gorgonio wind farm. Data show a positive lapse rate at 4 AM and negative lapse rates at 10 AM and 4 PM at the base during the field campaign (Fig. 2B). The corresponding temperature signal from the San Gorgonio wind farm (Fig. 2A) shows a warming effect at 4 AM but a cooling effect at 10 AM and 4 PM. This pattern is consistent with the proposed hypothesis.

…

I’m not opposed to wind turbines, but please, let’s not presume to say that erecting them will have absolutely no effect on wind flow.

[kristopher]

24. You were doing fair but then you dropped to poor with your closing.

1) no one said you were opposed to wind turbines.
2) No one said that "erecting them will have absolutely no effect on wind flow".

Reviewers comments:
D.B. Kirk-Davidoff
1. Practical plans for generating electricity from winds aloft usual focus on the region from 1 km to 3 km in elevation. This is not only for technological reasons reasons (fewer concerns about interference with aviation, lower cost, mass of the kite tether) but also because decreasing atmospheric density with heigh means that for turbines of a given size, available power is not much greater at 10 km than at 3 km (Lansdorp and Ockels, 2005). It would be interesting to see how turbines more directly related to actual proposed systems would influence the winds aloft.

2. More generally, the enormous ratio between the 480 TW of atmospheric and surface dissipation lost due to the elevated wind turbines and the feeble 7 TW of wind power generated by the turbines suggests that something about the placement of the turbines in the study is very far from optimal for wind generation purposes! One suspects that the algorithm of choosing to place the turbines in region of highest winds at each instant results in a particularly strong impact on the jet. It would be interesting to see results from a set of fixed-location kite experiments at different altitudes and latitudes. One generally thinks of the Lorenz Energy cycle as being driven by the large scale (Lorenz, 1955). We should aim to tap energy from the system in locations somewhat removed from the main loci of conversion from kinetic energy of the mean flow to eddy kinetic energy (as shown in the figures in Li et al., 2007). Since the jet is one of those centers, it may be that Miller et al. have placed their wind generators in exactly the worst place to tap wind energy without interfering with the sources of surface wind energy.
http://www.earth-syst-dynam-discuss.net/2/C240/2011/esdd-2-C240-2011.pdf


Juan Carlos Bergmann
...The basic concept in MGK 2011 is correct and adequate: The energy density of the undisturbed flow and the associated pressure field’s energy represent a reservoir, which is rapidly depleted in case of large-scale energy extraction. MGK 2011 does not consider the processes of energy-replenishment to that reservoir, but focuses on depletion of the pressure gradient of the jets only. Fundamental difficulties created by that concept are discussed below.

DRAG ON THE JET STREAM... (4 para total)
...Thus, turbine drag is presented as friction-equivalent. Such conception is incorrect be- cause friction is completely dissipative, so that no electric energy can be provided by a ‘turbine’ that is a frictional apparatus, and all extracted energy is fed into the transformation chain via turbulent kinetic energy (TKE) and subsequent viscous dissipation to heat. In absence of phase boundaries like Earth’s surface, turbulence scales are very large in the horizontal, and their limitation in the vertical is defined by the buoy- ancy forces in the stable stratification present in upper troposphere. As discussed in Bergmann (2010a, 2010b), real turbines with good efficiency (little friction!) do not produce significant amounts of (additional) TKE. There is a general misconception in the wind energy meteorology ‘community’ that interprets turbine drag as friction-equivalent – in analogy to natural flow obstacles like trees – and MGK 2011 reproduces it. Trees’ wake flow is strongly turbulent and dissipates the extracted energy completely to heat, but turbines’ wake flow cannot do that if the rotating turbine extracts large amounts of non-dissipative energy by producing a torque about its axis.
...
DEPLETION OF THE ENERGY RESERVOIR...
...Figure 10 demonstrates that the modelled depletion (natural dissipation) (b) is about 20 times the modelled maximum extraction (c). Figure 6 demonstrates that meridional flow is reversed in case of maximum extraction (up-gradient flow turns into down-gradient flow), despite minimal energy extraction, which could only replace ca. 5% of dissipation (at constant replenishment rate of the energy reservoir). These enormous discrepancies indicate severe misconceptions of jet energetics.

CONCLUDING REMARKS
In conclusion, drag (momentum-related) parameterisation of energy transformations in the numerical model is highly contradictory and cannot account for basic energetics of the real jets. The analytical energy-reservoir depletion concept is insufficient because a depleting reservoir’s steady state value is necessarily zero. (The analytical concept is implicitly built on an infinite reservoir.) A real steady-sate value is necessarily determined by the processes that replenish the energy reservoir of the pressure field, which in its turn determines the power density of the flow and the maximal extractable power. MGK 2011’s concept of pressure-gradient depletion is an example for introduction of unphysical conditions through parameterisation, and it is surely not the only one in atmospheric sciences. Physical reasoning reveals directly (without utilisation of numerical models) that no additional wind power can be gained and that the jets’ resource must be very small. In regard to the impacts, specified detailed statements should only be made on the basis of models, which explicitly consider complete jet physics.
http://www.earth-syst-dynam-discuss.net/2/C244/2011/esdd-2-C244-2011.pdf

[kristopher]

8. Here is a 2009 study on the topic

Global Assessment of High-Altitude Wind Power
Cristina L. Archer 1,* and Ken Caldeira 2

http://www.mdpi.com/1996-1073/2/2/307/pdf


It will be interesting to see how the discussion proceeds. A claim similar to that in the OP (but concerning low-level wind) came out of MIT a couple of years ago and it turned out that the resolution of the modeling assumed turbines occupied all space in each grid cell examined, so its conclusion was not able to be substantiated.