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
On 02/04/2011 14:15, Alvia Gaskill 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:geoengineering@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.
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