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
----- Original Message -----
From: Alvia Gaskill
To: [email protected] ; geoengineering
Sent: Saturday, April 02, 2011 9:15 AM
Subject: Re: [geo] Wind and wave energies are not renewable after all
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
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.
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