Wind and wave energies are not renewable after all

[Andrew Lockley]

Wind and wave energies are not renewable after all

• 30 March 2011 by Mark Buchanan
• Magazine issue 2806. Subscribe and save
• For similar stories, visit the Energy and Fuels and Climate Change Topic Guides

Editorial: "The sun is our only truly renewable energy source"

Build enough wind farms to replace fossil fuels and we could do as much damage to the climate as greenhouse global warming

WITNESS a howling gale or an ocean storm, and it's hard to believe that humans could make a dent in the awesome natural forces that created them. Yet that is the provocative suggestion of one physicist who has done the sums.

He concludes that it is a mistake to assume that energy sources like wind and waves are truly renewable. Build enough wind farms to replace fossil fuels, he says, and we could seriously deplete the energy available in the atmosphere, with consequences as dire as severe climate change.

Axel Kleidon of the Max Planck Institute for Biogeochemistry in Jena, Germany, says that efforts to satisfy a large proportion of our energy needs from the wind and waves will sap a significant proportion of the usable energy available from the sun. In effect, he says, we will be depleting green energy sources. His logic rests on the laws of thermodynamics, which point inescapably to the fact that only a fraction of the solar energy reaching Earth can be exploited to generate energy we can use.

When energy from the sun reaches our atmosphere, some of it drives the winds and ocean currents, and evaporates water from the ground, raising it high into the air. Much of the rest is dissipated as heat, which we cannot harness.

At present, humans use only about 1 part in 10,000 of the total energy that comes to Earth from the sun. But this ratio is misleading, Kleidon says. Instead, we should be looking at how much useful energy - called "free" energy in the parlance of thermodynamics - is available from the global system, and our impact on that.

Humans currently use energy at the rate of 47 terawatts (TW) or trillions of watts, mostly by burning fossil fuels and harvesting farmed plants, Kleidon calculates in a paper to be published in Philosophical Transactions of the Royal Society. This corresponds to roughly 5 to 10 per cent of the free energy generated by the global system.

"It's hard to put a precise number on the fraction," he says, "but we certainly use more of the free energy than [is used by] all geological processes." In other words, we have a greater effect on Earth's energy balance than all the earthquakes, volcanoes and tectonic plate movements put together.

Radical as his thesis sounds, it is being taken seriously. "Kleidon is at the forefront of a new wave of research, and the potential prize is huge," says Peter Cox, who studies climate system dynamics at the University of Exeter, UK. "A theory of the thermodynamics of the Earth system could help us understand the constraints on humankind's sustainable use of resources." Indeed, Kleidon's calculations have profound implications for attempts to transform our energy supply.

Of the 47 TW of energy that we use, about 17 TW comes from burning fossil fuels. So to replace this, we would need to build enough sustainable energy installations to generate at least 17 TW. And because no technology can ever be perfectly efficient, some of the free energy harnessed by wind and wave generators will be lost as heat. So by setting up wind and wave farms, we convert part of the sun's useful energy into unusable heat.

"Large-scale exploitation of wind energy will inevitably leave an imprint in the atmosphere," says Kleidon. "Because we use so much free energy, and more every year, we'll deplete the reservoir of energy." He says this would probably show up first in wind farms themselves, where the gains expected from massive facilities just won't pan out as the energy of the Earth system is depleted.

Using a model of global circulation, Kleidon found that the amount of energy which we can expect to harness from the wind is reduced by a factor of 100 if you take into account the depletion of free energy by wind farms. It remains theoretically possible to extract up to 70 TW globally, but doing so would have serious consequences.

Although the winds will not die, sucking that much energy out of the atmosphere in Kleidon's model changed precipitation, turbulence and the amount of solar radiation reaching the Earth's surface. The magnitude of the changes was comparable to the changes to the climate caused by doubling atmospheric concentrations of carbon dioxide (Earth System Dynamics, DOI: 10.5194/esd-2-1-2011).

"This is an intriguing point of view and potentially very important," says meteorologist Maarten Ambaum of the University of Reading, UK. "Human consumption of energy is substantial when compared to free energy production in the Earth system. If we don't think in terms of free energy, we may be a bit misled by the potential for using natural energy resources."

This by no means spells the end for renewable energy, however. Photosynthesis also generates free energy, but without producing waste heat. Increasing the fraction of the Earth covered by light-harvesting vegetation - for example, through projects aimed at "greening the deserts" - would mean more free energy would get stored. Photovoltaic solar cells can also increase the amount of free energy gathered from incoming radiation, though there are still major obstacles to doing this sustainably (see "Is solar electricity the answer?").

In any event, says Kleidon, we are going to need to think about these fundamental principles much more clearly than we have in the past. "We have a hard time convincing engineers working on wind power that the ultimate limitation isn't how efficient an engine or wind farm is, but how much useful energy nature can generate." As Kleidon sees it, the idea that we can harvest unlimited amounts of renewable energy from our environment is as much of a fantasy as a perpetual motion machine.

Is solar electricity the answer?

A solar energy industry large enough to make a real impact will require cheap and efficient solar cells. Unfortunately, many of the most efficient of today's thin-film solar cells require rare elements such as indium and tellurium, whose global supplies could be depleted within decades.

For photovoltaic technology to be sustainable, it will have to be based on cheaper and more readily available materials such as zinc and copper, says Kasturi Chopra of the Indian Institute of Technology, New Delhi.

Researchers at IBM showed last year that they could produce solar cells from these elements along with tin, sulphur and the relatively rare element selenium. These "kesterite" cells already have an efficiency comparable with commercially competitive cells, and it may one day be possible to do without the selenium.

Even if solar cells like this are eventually built and put to work, they will still contribute to global warming. That is because they convert only a small fraction of the light that hits them, and absorb most of the rest, converting it to heat that spills into the environment. Sustainable solar energy may therefore require cells that reflect the light they cannot use.

[Alvia Gaskill]

Wind and wave energy are the result of the conversion of solar energy into kinetic energy, i.e. the motion of molecules.  Once converted into kinetic energy it's a use it or lose it proposition.  Extracting kinetic energy from the atmosphere or the ocean doesn't mean it won't be replaced by more energy from sunlight.  Planting more trees will also intercept winds, albeit without the electricity generation.  Who funded this research?  The same people who want to prevent contact with alien civilizations?  I note that the Royal Society was also a party to that one too.  Note to Royal Society.  When you actually find something under the bed I should be afraid of, wake me up.

--
You received this message because you are subscribed to the Google Groups "geoengineering" group.
To post to this group, send email to geoengi...@googlegroups.com.
To unsubscribe from this group, send email to geoengineerin...@googlegroups.com.
For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en.

[Dan Whaley]

Since one of the issues w/ warming is that the atmosphere can hold
more energy-- more precip, storms & wilder weather-- i suppose
removing some excess could be considered a form of geoengineering...

"The magnitude of the
changes was comparable to the changes to the climate caused by
doubling
atmospheric concentrations of carbon dioxide"

Similar magnitude maybe, but opposite sign.

As always, the answer is that we need a portfolio. Duh.

BTW... isn't this an old story? Heard people talking about this a
couple years ago.

D

On Apr 2, 6:15 am, "Alvia Gaskill" <agask...@nc.rr.com> wrote:
> Wind and wave energy are the result of the conversion of solar energy into kinetic energy, i.e. the motion of molecules.  Once converted into kinetic energy it's a use it or lose it proposition.  Extracting kinetic energy from the atmosphere or the ocean doesn't mean it won't be replaced by more energy from sunlight.  Planting more trees will also intercept winds, albeit without the electricity generation.  Who funded this research?  The same people who want to prevent contact with alien civilizations?  I note that the Royal Society was also a party to that one too.  Note to Royal Society.  When you actually find something under the bed I should be afraid of, wake me up.
>
>
>
>
>
>
>
>   ----- Original Message -----
>   From: Andrew Lockley
>   To: geoengineering
>   Sent: Friday, April 01, 2011 8:10
>   Subject: [geo] Wind and wave energies are not renewable after all
>
>   Wind and wave energies are not renewable after all

>     a.. 30 March 2011 by Mark Buchanan
>     b.. Magazine issue 2806. Subscribe and save
>     c.. For similar stories, visit the Energy and Fuels and Climate Change Topic Guides

[Stephen Salter]

Andrew

Most of the energy in waves is at present dissipated as heat in water and sand at the beach.  Data on the North Atlantic wave climate combined with the flow of the North Atlantic Drift suggest an increase in temperature on the beach by about 1/50 of a degree Celsius.

If we built very efficient wave plant all the way along the coast we might reduce the temperature increase to 1/100 of a degree.  But as we would be using the wave-generated electricity in homes and factories, most will end up warming the prevailing wind which is exchanging heat with the sea.  The overall effect is a short diversion.

Onshore wind turbines do produce a detectable increase in the evaporation rate of ground water leading to a lower river run-off and we should expect offshore wind turbines to increase evaporation from the sea which ought to restore run-off.  It may be possible to design floating wind-driven machines which produce no electricity but put all the energy they extract into increasing the turbulence of the lower atmosphere over the sea.  This should produce more rainfall down wind.

Stephen

Emeritus Professor of Engineering Design
Institute for Energy Systems
School of Engineering
Mayfield Road
University of Edinburgh EH9  3JL
Scotland
Tel +44 131 650 5704
Mobile 07795 203 195
www.see.ed.ac.uk/~shs

[Nando]

My reading of the article suggested that the authors of the study were principally claiming that wind has an impact on climate, so it is already being "used". What wasn't clear from the article was what type of impact reducing the energy level of winds all over the globe through the prolific use of wind turbines might have. In a warming world, I understand we should expect stronger winds. On a simplistic generalized level that might not be relevant to local climate, slowing those stronger winds down might have an ameliorating effect on climate change. Hence the claim that "The magnitude of the changes was comparable to the changes to the climate caused by doubling atmospheric concentrations of carbon dioxide" might not be as bad as it is made to seem.

As usually, I'm grasping at straws, but as a layman, that's what stood out for me.

Nando

--
Nando M. Breiter
The CarbonZero Project
CP 234
6934 Bioggio
Switzerland

+41 91 606 6372

na...@carbonzero.ch
www.carbonzero.ch

[JohnDuke]

Indeed, the authors do not appear to understand that a watt (joule/second) is a rate of energy conversion, not a unit of energy. If energy is converted slower here, there is more to convert there.

A more interesting line of inquiry is the evaporation effect of slowing down surface wind (but not upper lever wind). Also re protecting crops from extreme wind damage etc....the significant effect of wind turbines is to thicken the boundary layer.

John Duke

[rongre...@comcast.net]

Nando etal:

   1.   I take a different message from the original article by Axel Kleidon - still without a date to be published.  The first material below is found at:
    http://www.newscientist.com/article/mg21028063.300-wind-and-wave-energies-are-not-renewable-after-all.html?page=1
   
   2    A draft version of the Kleidon article, submitted about three weeks ago, and noted in the above article, is found at:
   http://arxiv.org/abs/1103.2014

   3.  The article's  message for me is not about wind and waves.  It is about the biosphere. Near the end (and I think that should be read first by many of us),  Kleidon calls for a doubling of NPP.  This is a call consistent with the CDR half of Geoengineering of main interest to you and I:  Biochar.  I believe his conclusion is only marginally consistent with other parts of CDR or Geoengineering.

   4.   I recommend all of his five diagrams - but especially the last several, which are new me.  All are expressed in TW rather than GtC/yr terms - but the carbon implications are all spelled out.

   5.  I concur with your final comment below, as well - but believe we should look at Kleidon's analysis primarily from the aspect of our global biosphere.

Ron

[vogle...@gmail.com]

Hi All, Last year I read a short comment by Dr. Caldera on "High Wind" energy harvesting posted on Bill Gates website http://www.thegatesnotes.com/Conversations/What-About-Wind. Dr. Caldera stated "if we were to meet future power demand by this source exclusively, we must intercept more than 1% of natural flows. I think when we get above a 1% change in a natural system, we need to be concerned about large scale unintended consequences.". And, now I see this report by Dr. Kleidon reporting concerns about Boundary Layer Winds and Wave Energy. I am somewhat disappointed that such exotic extrapolations are getting serious play on the issue of renewable energy.

First, I believe Dr. Gaskill statement in this tread is the the clearest thinking on this issue of the use of these renewable energies. This planet is in fact solar powered and the solar energy that it receives is far more than we can use. Also, Boundary Layer winds are effected by the difference between the rotational speed of the planet and that of the total (fluid) mass of the atmosphere. High altitude winds also get impacted by this differential to a certain degree. Wave energy has not just the solar energy input, but, the added lunar diurnal gravitational influence.

I am not an expert in any shape or form, but, I have twirled a coffee cup and watched how the "boundary friction" between the cup and fluid causes the fluid to move. And, I have stood by the shore and watched the force of a tide rise and fall and watched the wave production from that force. On a global scale, these basic physical forces are clearly significant enough to be considered into the equation. Looking beyond just the solar energy input/effect seems worth factoring into these types of calculations.

We should not be looking to calculate any renewable energy option into the ground. We will need all of them (including High Wind) to power our civilization.

Dr. Gaskill, when they wake you up, I'll cook breakfast!

[Veli Albert Kallio]

Although I am member of Environmentalists For Nuclear (EFN) I suspect that it is our nuclear sponsors and Australian uranium mining who have concocted this concern of winds running out in the aftermath of Japan nuclear disaster in order to dismiss the renewables as serious alternative. In any case, it will take decades to build such capacity which should not be our immediate concern at all.  Albert
 

---

Date: Sat, 2 Apr 2011 20:17:40 +0000
Subject: Re: Re: [geo] Wind and wave energies are not renewable after all
From: vogle...@gmail.com
To: d.n...@gmail.com
CC: agas...@nc.rr.com; andrew....@gmail.com; geoengi...@googlegroups.com

[Ken Caldeira]

It is hard for me to understand why this unpublished paper is getting so much attention, when it seems to be a rather fanciful and quasi-religious account of how the Earth functions as a system.  I believe Kleidon's entire conceptual framework to be suspect.

A typical passage:

Then, the central question is going to be whether this increase in human activity is going to be met by depleting existing stocks of free energy, and thereby reduce the ability of the planet to generate free energy (because natural generation processes are likely to operate at maximum efficiency, so that any human appropriation ought to diminish the ability to generate this free energy), or whether these demands will be met by enhancing the ability of the earth system to generate free energy

The claim that "natural generation processes are likely to operate at maximum efficiency" is probably not even a parsable statement about the real world. (Natural generation processes simply follow laws of physics. We talk about efficiency only when we talk about achieving objectives, and the natural world has no objectives.) I have criticized Kleidon's conceptual framework elsewhere (see attachment [Caldeira, 2007]). The natural world does not optimize, it merely exists.

---

On a more technical note, Peixoto and Oort put the global dissipation rate of kinetic energy in the atmosphere to be on the order of 10^15 W. Kleidon estimates that the dissipation rate of energy produced by thermal gradients is on the order of 6.17 x 10^15 TW.

Drag parameterizations within climate models are probably not good to within 1%, so if a broadly distributed 1% change in this dissipation rate would radically alter climate, then existing climate models could not reasonably reproduce today's climate.  (Of course if you put all of this extra dissipation in a small number of grid cells, that could have some effects.)  

While accepting that there could be significant effects of patchy wind farms deployed at civilization scale (17 TW), I do not believe that harvesting wind energy at the scale of 1% of the global dissipation rate is going to have major climate effects if broadly distributed.

Note also that the climate effects of wind turbines scale with the amount of power generation (dissipation), whereas the effects of greenhouse gases accumulate in time and so to a first approximation scale with the time integral of power generation. Constant wind power generation rates produce a constant level of environmental disturbance. Constant rates of CO2 emission produce increasing levels of environmental disturbance. The question is, how long will it be before wind power is environmentally preferable to fossil-fuel power with CO2 release to the atmosphere?

My assessment is that from an environmental perspective wind power is clearly already preferable to fossil-fuels without CCS. (Of course, from perspectives of monetized costs and reliability of electricity production, fossil-fuels have wind beat.)

As Hofffert et al (1998, 2002) have pointed out, we are going to need tens of TW of carbon-neutral power in the coming decades. To acheive this, it is likely that some individual technologies will need to be able to provide power at the 10 TW scale.

There are not that many technologies that can do this:  solar, wind, nuclear, fossil-fuels with CCS (and if you are truly an optimist, you can add biomass to this list).

In short, I would not let paper's like Axel Kleidon's distract us from the facts.

Best,

Ken

PS. I like Axel Kleidon and think he is a bright and creative thinker. Unfortunately, his idiosyncratic world view appears to lead him to raise alarm where no alarm is needed. Nevertheless, incorrect work such as this can play a useful role in spurring others to more carefully assess the facts. Big decisions are ahead of us, and we want to avoid making big mistakes.

PPS. I wish I had copy-edited my attached response to Kleidon a bit more before publishing.

___________________________________________________
Ken Caldeira

Carnegie Institution Dept of Global Ecology
260 Panama Street, Stanford, CA 94305 USA
+1 650 704 7212 kcal...@carnegie.stanford.edu
http://dge.stanford.edu/labs/caldeiralab  @kencaldeira

[David Keith]

Responding to a VERY old thread on wind power:

 

The only link to geoengineering here is that there is a possibility of manipulating wind turbine drag for weather control, see:

 

At 10’s TW scale extraction of wind does begin to be constrained by the generation of kinetic energy. I led the a joint NCAR-GFDL group that published the first paper on this topic see:

David W. Keith et al, The influence of large-scale wind-power on global climate. Proceedings of the National Academy of Sciences, 101, p. 16115-16120.

http://people.ucalgary.ca/~keith/papers/66.Keith.2004.WindAndClimate.e.pdf

 

See http://people.ucalgary.ca/~keith/papers/94.Kirk-Davidoff.SurfaceRoughnessJAS.p.pdf for a paper that says a bit about why it happens.

 

The following web page gives and overview but it’s now out of date: http://people.ucalgary.ca/~keith/wind.html

 

Alvia’s comment that about “kinetic energy, i.e. the motion of molecules”, confuses the physics. Kinetic energy is macroscopic velocity, random motion of molecules is just heat. It is true that large scale production and dissipation of kinetic energy must balance, have a look at Peixoto and Oort’s the Physics of Climate or a short encyclopedia article I one wrote on atmospheric energetics: http://people.ucalgary.ca/~keith/papers/15.Keith.1996.Energetics.s.pdf

 

Bottom lines:

 

1. Commonly cited estimates for global wind power potential are too large. On cannot get to 100 TW in any practical scheme I know about.

 

2. At even a few TW large scale climate effects will begin to be important. But, this does not say we should not make a few TW of wind, just that--like any energy technology—there are tradeoffs.

 

David

[Govindasamy bala]

Hi David,

Couple of questions.
Generation of wind energy would increase the KE dissipation rate but this is not an external forcing to the climate system. I agree there would be local and regional climate changes but there should be no global mean warming. Right?

The current KE dissipation rate is about 2 watts/m^2. Over land, this translates to about 300 TW. Suppose wind farms extract 150 TW (which may be impractical), the dissipation rate over land will increase to 3 Wm^2. Don't you think the KE (or available PE) generation rate in the atmosphere would correspondingly increase? Of course these would be large regional climate changes.

Bala

Best wishes,

-------------------------------------------------------------------
Dr. G. Bala
Associate Professor
Center for Atmospheric and Oceanic Sciences
Indian Institute of Science
Bangalore - 560 012
India

Tel: +91 80 2293 2698
        +91 80 2293 2505 x206
Fax: +91 80 2360 0865
Email: gb...@caos.iisc.ernet.in
             bala.gov@gmail.com
Web:http://caos.iisc.ernet.in/faculty/gbala/gbala.html
-------------------------------------------------------------------

[Mike MacCracken]

Dear David--I was going to ask a similar question to Bala’s—as this has actually been an ongoing argument in some circles of the energy community, with a scientific study by a Royal Society lead physicist in their energy analysis talking about a limit based on extracting a share of the existing atmospheric KE and Mark Jacobson at Stanford saying there is plenty of KE as it will be restored.

It seems to me that the KE pulled out will be replaced—if not, the atmosphere would eventually not be moving and so a huge equator-pole temperature gradient would build up. With solar energy concentrated at the low latitudes and IR loss in excess at high latitudes, the atmosphere will be seeking balance; take some energy out and the atmosphere will try to restore it, rather like what happens when one puts a rock in a stream, maybe with a bit different flow, but I would not think significantly less KE. Right?

Mike

On 7/12/11 7:25 AM, "Govindasamy Bala" <bala...@gmail.com> wrote:

Hi David,

Couple of questions.
Generation of wind energy would increase the KE dissipation rate but this is not an external forcing to the climate system. I agree there would be local and regional climate changes but there should be no global mean warming. Right?

The current KE dissipation rate is about 2 watts/m^2. Over land, this translates to about 300 TW. Suppose wind farms extract 150 TW (which may be impractical), the dissipation rate over land will increase to 3 Wm^2. Don't you think the KE (or available PE) generation rate in the atmosphere would correspondingly increase? Of course these would be large regional climate changes.

Bala

On Tue, Jul 12, 2011 at 8:37 AM, David Keith <ke...@ucalgary.ca> wrote:

Responding to a VERY old thread on wind power:
 
The only link to geoengineering here is that there is a possibility of manipulating wind turbine drag for weather control, see:
 
At 10’s TW scale extraction of wind does begin to be constrained by the generation of kinetic energy. I led the a joint NCAR-GFDL group that published the first paper on this topic see:
David W. Keith et al, The influence of large-scale wind-power on global climate. Proceedings of the National Academy of Sciences, 101, p. 16115-16120.

http://people.ucalgary.ca/~keith/papers/66.Keith.2004.WindAndClimate.e.pdf <http://people.ucalgary.ca/%7Ekeith/papers/66.Keith.2004.WindAndClimate.e.pdf>  
 
See http://people.ucalgary.ca/~keith/papers/94.Kirk-Davidoff.SurfaceRoughnessJAS.p.pdf <http://people.ucalgary.ca/%7Ekeith/papers/94.Kirk-Davidoff.SurfaceRoughnessJAS.p.pdf>  for a paper that says a bit about why it happens.
 
The following web page gives and overview but it’s now out of date: http://people.ucalgary.ca/~keith/wind.html <http://people.ucalgary.ca/%7Ekeith/wind.html>
 
Alvia’s comment that about “kinetic energy, i.e. the motion of molecules”, confuses the physics. Kinetic energy is macroscopic velocity, random motion of molecules is just heat. It is true that large scale production and dissipation of kinetic energy must balance, have a look at Peixoto and Oort’s the Physics of Climate or a short encyclopedia article I one wrote on atmospheric energetics: http://people.ucalgary.ca/~keith/papers/15.Keith.1996.Energetics.s.pdf <http://people.ucalgary.ca/%7Ekeith/papers/15.Keith.1996.Energetics.s.pdf>  

 
Bottom lines:
 
1. Commonly cited estimates for global wind power potential are too large. On cannot get to 100 TW in any practical scheme I know about.
 
2. At even a few TW large scale climate effects will begin to be important. But, this does not say we should not make a few TW of wind, just that--like any energy technology—there are tradeoffs.
 
David
 

From: geoengi...@googlegroups.com [mailto:geoengi...@googlegroups.com] On Behalf Of Nando
Sent: Saturday, April 02, 2011 8:25 AM
To: agas...@nc.rr.com
Cc: andrew....@gmail.com; geoengineering
Subject: Re: [geo] Wind and wave energies are not renewable after all
 
My reading of the article suggested that the authors of the study were principally claiming that wind has an impact on climate, so it is already being "used". What wasn't clear from the article was what type of impact reducing the energy level of winds all over the globe through the prolific use of wind turbines might have. In a warming world, I understand we should expect stronger winds. On a simplistic generalized level that might not be relevant to local climate, slowing those stronger winds down might have an ameliorating effect on climate change. Hence the claim that "The magnitude of the changes was comparable to the changes to the climate caused by doubling atmospheric concentrations of carbon dioxide" might not be as bad as it is made to seem.

 

As usually, I'm grasping at straws, but as a layman, that's what stood out for me.

 

Nando

On Sat, Apr 2, 2011 at 3:15 PM, Alvia Gaskill <agas...@nc.rr.com> wrote:

Wind and wave energy are the result of the conversion of solar energy into kinetic energy, i.e. the motion of molecules.  Once converted into kinetic energy it's a use it or lose it proposition.  Extracting kinetic energy from the atmosphere or the ocean doesn't mean it won't be replaced by more energy from sunlight.  Planting more trees will also intercept winds, albeit without the electricity generation.  Who funded this research?  The same people who want to prevent contact with alien civilizations?  I note that the Royal Society was also a party to that one too.  Note to Royal Society.  When you actually find something under the bed I should be afraid of, wake me up.

----- Original Message -----

From: Andrew Lockley <mailto:and...@andrewlockley.com>

To: geoengineering <mailto:geoengi...@googlegroups.com>

Sent: Friday, April 01, 2011 8:10

Subject: [geo] Wind and wave energies are not renewable after all

 
Wind and wave energies are not renewable after all

·         30 March 2011 by Mark Buchanan <http://www.newscientist.com/search?rbauthors=Mark+Buchanan>
·         Magazine issue 2806 <http://www.newscientist.com/issue/2806> . Subscribe and save <http://www.newscientist.com/subscribe?promcode=nsarttop>
·         For similar stories, visit the Energy and Fuels <http://www.newscientist.com/topic/energy-fuels>  and Climate Change <http://www.newscientist.com/topic/climate-change>  Topic Guides

Editorial: "The sun is our only truly renewable energy source <http://www.newscientist.com/article/mg21028062.500-the-sun-is-our-only-truly-renewable-energy-source.html> "

Build enough wind farms to replace fossil fuels and we could do as much damage to the climate as greenhouse global warming
WITNESS a howling gale or an ocean storm, and it's hard to believe that humans could make a dent in the awesome natural forces that created them. Yet that is the provocative suggestion of one physicist who has done the sums.
He concludes that it is a mistake to assume that energy sources like wind and waves are truly renewable. Build enough wind farms to replace fossil fuels, he says, and we could seriously deplete the energy available in the atmosphere, with consequences as dire as severe climate change.
Axel Kleidon of the Max Planck Institute for Biogeochemistry in Jena, Germany, says that efforts to satisfy a large proportion of our energy needs from the wind and waves will sap a significant proportion of the usable energy available from the sun. In effect, he says, we will be depleting green energy sources. His logic rests on the laws of thermodynamics, which point inescapably to the fact that only a fraction of the solar energy reaching Earth can be exploited to generate energy we can use.
When energy from the sun reaches our atmosphere, some of it drives the winds and ocean currents, and evaporates water from the ground, raising it high into the air. Much of the rest is dissipated as heat, which we cannot harness.
At present, humans use only about 1 part in 10,000 of the total energy that comes to Earth from the sun. But this ratio is misleading, Kleidon says. Instead, we should be looking at how much useful energy - called "free" energy in the parlance of thermodynamics - is available from the global system, and our impact on that.

Humans currently use energy at the rate of 47 terawatts (TW) or trillions of watts, mostly by burning fossil fuels and harvesting farmed plants, Kleidon calculates in a paper to be published in Philosophical Transactions of the Royal Society <http://arxiv.org/abs/1103.2014> . This corresponds to roughly 5 to 10 per cent of the free energy generated by the global system.

"It's hard to put a precise number on the fraction," he says, "but we certainly use more of the free energy than [is used by] all geological processes." In other words, we have a greater effect on Earth's energy balance than all the earthquakes, volcanoes and tectonic plate movements put together.
Radical as his thesis sounds, it is being taken seriously. "Kleidon is at the forefront of a new wave of research, and the potential prize is huge," says Peter Cox, who studies climate system dynamics at the University of Exeter, UK. "A theory of the thermodynamics of the Earth system could help us understand the constraints on humankind's sustainable use of resources." Indeed, Kleidon's calculations have profound implications for attempts to transform our energy supply.
Of the 47 TW of energy that we use, about 17 TW comes from burning fossil fuels. So to replace this, we would need to build enough sustainable energy installations to generate at least 17 TW. And because no technology can ever be perfectly efficient, some of the free energy harnessed by wind and wave generators will be lost as heat. So by setting up wind and wave farms, we convert part of the sun's useful energy into unusable heat.
"Large-scale exploitation of wind energy will inevitably leave an imprint in the atmosphere," says Kleidon. "Because we use so much free energy, and more every year, we'll deplete the reservoir of energy." He says this would probably show up first in wind farms themselves, where the gains expected from massive facilities just won't pan out as the energy of the Earth system is depleted.
Using a model of global circulation, Kleidon found that the amount of energy which we can expect to harness from the wind is reduced by a factor of 100 if you take into account the depletion of free energy by wind farms. It remains theoretically possible to extract up to 70 TW globally, but doing so would have serious consequences.

Although the winds will not die, sucking that much energy out of the atmosphere in Kleidon's model changed precipitation, turbulence and the amount of solar radiation reaching the Earth's surface. The magnitude of the changes was comparable to the changes to the climate caused by doubling atmospheric concentrations of carbon dioxide (Earth System Dynamics, DOI: 10.5194/esd-2-1-2011 <http://dx.doi.org/10.5194/esd-2-1-2011> ).

"This is an intriguing point of view and potentially very important," says meteorologist Maarten Ambaum of the University of Reading, UK. "Human consumption of energy is substantial when compared to free energy production in the Earth system. If we don't think in terms of free energy, we may be a bit misled by the potential for using natural energy resources."

This by no means spells the end for renewable energy, however. Photosynthesis also generates free energy, but without producing waste heat. Increasing the fraction of the Earth covered by light-harvesting vegetation - for example, through projects aimed at "greening the deserts" - would mean more free energy would get stored. Photovoltaic solar cells can also increase the amount of free energy gathered from incoming radiation, though there are still major obstacles to doing this sustainably (see "Is solar electricity the answer?") <http://www.newscientist.com/article/mg21028063.300-wind-and-wave-energies-are-not-renewable-after-all.html?full=true#bx280633B1> .

In any event, says Kleidon, we are going to need to think about these fundamental principles much more clearly than we have in the past. "We have a hard time convincing engineers working on wind power that the ultimate limitation isn't how efficient an engine or wind farm is, but how much useful energy nature can generate." As Kleidon sees it, the idea that we can harvest unlimited amounts of renewable energy from our environment is as much of a fantasy as a perpetual motion machine.

Is solar electricity the answer?

A solar energy industry large enough to make a real impact will require cheap and efficient solar cells. Unfortunately, many of the most efficient of today's thin-film solar cells require rare elements such as indium and tellurium, whose global supplies could be depleted within decades <http://www.newscientist.com/article/dn16550-why-sustainable-power-is-unsustainable.html> .

For photovoltaic technology to be sustainable, it will have to be based on cheaper and more readily available materials such as zinc and copper, says Kasturi Chopra of the Indian Institute of Technology, New Delhi.

Researchers at IBM showed last year that they could produce solar cells from these elements <http://onlinelibrary.wiley.com/doi/10.1002/adma.200904155/abstract;jsessionid=A766B41341BD4059B74B2F28AE9B8A80.d03t03?systemMessage=Wiley+Online+Library+will+be+disrupted+2nd+Apr+from+10-12+BST+for+monthly+maintenance>  along with tin, sulphur and the relatively rare element selenium. These "kesterite" cells already have an efficiency comparable with commercially competitive cells, and it may one day be possible to do without the selenium.
Even if solar cells like this are eventually built and put to work, they will still contribute to global warming. That is because they convert only a small fraction of the light that hits them, and absorb most of the rest, converting it to heat that spills into the environment <http://www.newscientist.com/article/mg20026845.200-heat-we-emit-could-warm-the-earth.html> . Sustainable solar energy may therefore require cells that reflect the light they cannot use.

[Andrew Lockley]

If anything, an obstruction or impediment to fluid flows resulting from wind energy extraction will tend to reduce heat redistribution, and that will help restore the temperature differential between tropics and poles which has been harmed by the polar amplification of global warming

Logically, it will help to restore the polar ice, or at least prevent it from retreating further as fast.

It could even help maintain ocean circulation, and help prevent an anoxic event.

A

[David Keith]

Mike & Bala

 

A few answers:

 

First there is almost no link to geo here so we should probably take this off this list. The only (weak link) is weather control, see: http://www.atmos-chem-phys.org/10/769/2010/acp-10-769-2010.html

 

1. Bala said “Generation of wind energy would increase the KE dissipation rate but this is not an external forcing to the climate system.” And “The current KE dissipation rate is about 2 watts/m^2. Over land, this translates to about 300 TW. Suppose wind farms extract 150 TW (which may be impractical), the dissipation rate over land will increase to 3 Wm^2. Don't you think the KE (or available PE) generation rate in the atmosphere would correspondingly increase? Of course these would be large regional climate changes.”

 

Answer: As the surface drag is increased the total dissipation does not change much. That is, as you increase the KE sink in some locations with wind turbines the dissipation decreases elsewhere keeping total about constant. See Figure 2 of our 2004 PNAS where we tried this. This is what one would expect because dissipation of KE must balance its creation from APE (see pexoto and ort or my encyclopedia article cited below for an overview of atmo energetics). Going a bit deeper one might think that with more to “push against” the APE generation rate would go up and the atmo heat engine get more efficient, Kerry Emanuel have suggested to me that this should not be true because of a maximum entropy principle that I do not fully understand.

Bottom line: very likely Bala’s assumption is wrong.

 

2. Bala said: “I agree there would be local and regional climate changes but there should be no global mean warming. Right?”

 

Answer: mostly. One can see either warming or cooling depending on where the wind drag is applied. The point is that (a) climate changes due to drag are non-local, and (b) they can be large.

 

3. Mike asked about the Jacobsen paper that says no effect.

 

Answer: I think this paper is just wrong. If it were true I could violate the first law by extracting power without altering KE and then using that power to increase APE generating infinite power with no input. Nice trick.  There are now about 5 studies that confirm the broad results in our 2004 paper. The Jacobsen paper is an outlier. I expect a convincing critique will be published in the next few years.

 

Yours,
David

--

[Mike MacCracken]

A few further thoughts. The driving force for atmospheric motions is the equator-pole temperature gradient—energy continues to come in and decrease entropy (that is, enhancing the gradient), and then the motions tend to increase the entropy (trying to smooth out the gradient).

I guess what wind power really does is create an alternate form of dissipation to small eddies moving vegetation and just dissipating heat. So, instead of local heat dissipation by the vegetation (entropy increase), the energy is drained by windmills and then the electricity is dissipated as heat, so it is an alternative pathway. And I gather what you find is that the atmosphere above does not really care if the dissipation is locally friction heat loss or goes through the wind power bypass, doing some useful work for humanity. I guess that is just sort of saying that having fully efficient wind power machines would be no different than having higher orography, as far as the atmospheric circulation is concerned. So, then the question is what fraction of the surface friction that one can replace with wind power machines.

While you did the calculation for land areas, there is really no reason that one could not have floating windmills out over the ocean, diverting energy away from the wind driven currents and evaporation.

If one could develop the optimal machine, one could potentially extract energy at the rate that it is created by the differences in energy being supplied and radiated away from low and high latitudes, not wasting any energy in wind, etc.--so there is a theoretical upper limit—the supply is not infinite. But, the amount available could be pretty large using large windmills, tethered wind turbines in the jet stream, etc.--for an interim period, this would likely cause an increase in the gradient, but ultimately the limiting rate of removal of energy is the pole-equator difference (times some fractional potential efficiency).

As for the Jacobson calculation, the US is a pretty small area and so I would think creating a stronger drag over it would tend to attract energy in from elsewhere as Nature likes to push down gradients. This can take time, but there surely will be some infilling, especially given large scale motions due to the atmospheric circulation. Interesting.

Mike

[rongre...@comcast.net]

List and 4 ccs

   I remembered Dr. Axel Kleidon discussing a similar topic a few months ago, and I had later had some valuable off-list conversations on non-equilibrium thermodynamics and photosynthesis.  So I thought his view on this topic would be of value and interest and asked him to comment on the topic of the messages following. Note especially the abstract he has supplied.   He has approved my sending this.:  He replied to me:

"Here are a few points:

* Natural limits to wind power:  The generation of large-scale motion is limited by the heating gradient that forms from the absorption of solar irradiation between the tropics and the extratropics.  This gradient is the one that drives the atmospheric heat engine.  Similar to the Carnot limit (which involves considerations of entropy exchange, so that one does not come up with perpetuum motion machines), the maximum efficiency by which this heating gradient can be converted into motion is about 2%, yielding a maximum power of about 900 TW associated with atmospheric motion.  Estimates based on observations fall into the same order, as well as sensitivity simulations with general circulation models.  In other words, atmospheric motion is very likely associated with the maximum rate that is thermodynamically possible at which kinetic energy is generated (or at least operating close to this maximum).  So to argue that the kinetic energy will magically be replenished when it is extracted by wind turbines violates thermodynamic limits.  

* Wind speed vs. wind power:  The stock of kinetic energy (i.e. wind speed) is not a measure of how much wind power there is.  After all, we do not deal with an infinite stock of kinetic energy, but it needs to be continuously generated (it is re-generated on a time scale of about 10 days).  A prime example for this are the jet streams, regions of high wind speeds in the upper atmosphere.  They do not result from a strong power source, but from the near absence of friction.  This, in meteorology, is referred to as geostrophic flow.  Hence, you cannot generate much wind power from high altitude winds.  Our maximum estimate of 7.5 TW is two orders of magnitude less than what Ken Caldeira thinks, but consistent with the near geostrophic nature of jet streams.  We just submitted a study on this and it is currently in review. Here is a link to the MS:  <http://www.earth-syst-dynam-discuss.net/2/435/2011/esdd-2-435-2011.html>.  Ken Caldeira thinks we are wrong, but two reviewers (meteorologists) are very positive about it.  In addition, there will be dramatic climatic effects if one would extract 7.5 TW from the jet streams, causing havoc to the climate system.

* Impacts of wind turbines:  When kinetic energy is naturally dissipated by turbulence, it is not "wasted", but results in turbulent heat fluxes or in the generation of other forms of free energy, e.g. wave energy (over oceans).  When wind is naturally dissipated by friction, it is intimately linked with the cooling and mass exchange by turbulent heat fluxes (sensible heat, latent heat/evapotranspiration).  So when wind is not dissipated, but extracted by wind turbines, it must reduce turbulence, the associated turbulent heat fluxes, should result in a higher surface temperature, and thereby affects climate.  

Hope these comments help.  I am still amazed how smart and well-educated scientists in the field come up with reasoning that in the end are nothing but perpetuum motion machines.  Even though kinetic energy is, technically speaking, "free energy", it does not come for free.  It is not unlimited, and if you take a lot of wind out of the system, you'll feel the impact.

Best,
Axel

---

From: "Mike MacCracken" <mmac...@comcast.net>
To: "David Keith" <ke...@ucalgary.ca>, "Govindasamy Bala" <bala...@gmail.com>, "Ken Caldeira" <kcal...@stanford.edu>
Cc: "Geoengineering" <Geoengi...@googlegroups.com>
Sent: Tuesday, July 12, 2011 9:07:04 PM