'Transferring' energy isn't the same as doing something with it. 100% energy transfer is
like saying you can transfer gasoline from a can to your car without spilling any of it.
It's the conversion from photons to biomass that is inefficient.
The following is a breakdown of the energetics of the photosynthesis process from
Photosynthesis by Hall and Rao:[5]
Starting with the solar spectrum falling on a leaf,
47% lost due to photons outside the 400--700 nm active range (chlorophyll utilizes photons
between 400 and 700 nm, extracting the energy of one 700 nm photon from each one)
30% of the in-band photons are lost due to incomplete absorption or photons hitting
components other than chloroplasts
24% of the absorbed photon energy is lost due to degrading short wavelength photons to the
700 nm energy level
*68% of the utilized energy is lost in conversion into d-glucose*
35--45% of the glucose is consumed by the leaf in the processes of dark and
photo respiration
Stated another way:
100% sunlight ? non-bioavailable photons waste is 47%, leaving
53% (in the 400--700 nm range) ? 30% of photons are lost due to incomplete
absorption, leaving
37% (absorbed photon energy) ? 24% is lost due to wavelength-mismatch degradation to 700
nm energy, leaving
*28.2% (sunlight energy collected by chlorophyl) ? 32% efficient conversion of ATP and
NADPH to d-glucose, leaving*
9% (collected as sugar) ? 35--40% of sugar is recycled/consumed by the leaf in dark and
photo-respiration, leaving
5.4% net leaf efficiency.
Brent
On 11/8/2012 8:19 AM, Richard Ruquist wrote:
Excerpt: during photosynthesis, energy is transferred with 100 per cent efficiency from
one molecular machine to another.
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Entanglement Makes Quantum Batteries Almost Perfect, Say Physicists
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Posted: 07 Nov 2012 11:24 PM PST
In theory, quantum batteries such as atoms and molecules can store and release energy on
demand almost perfectly--provided they are entangled, says physicists
http://www.technologyreview.com/view/507176/entanglement-makes-quantum-batteries-almost-perfect-say-physicists/
In recent years, physicists have amused themselves by calculating the properties of
quantum machines, such as engines and refrigerators.
The essential question is how well these devices work when they exploit the rules of
quantum mechanics rather than classical mechanics. The answers have given physicists
important new insights into the link between quantum mechanics and thermodynamics.
The dream is that they may one day build such devices or exploit those already used by
nature.
Today, Robert Alicki, at the University of Gdansk in Poland, and Mark Fannes, at the
University of Leuven in Belgium, turn their attention to quantum batteries. They ask
how much work can be extracted from a quantum system where energy is stored temporarily.
Such a system might be an atom or a molecule, for example. And the answer has an
interesting twist.
Physicists have long known that it is possible to extract work from some quantum states
but not others. These others are known as passive states.
So the quantity physicists are interested in is the difference between the energy of the
quantum system and its passive states. All that energy is potentially extractable to do
work elsewhere.
Alicki and Fannes show that the extractable work is generally less than the
thermodynamic limit. In other words, they show that this kind of system isn't perfect.
However, the twist is that Alicki and Fannes say things change if you have several
identical quantum batteries that are entangled.
Entanglement is a strange quantum link that occurs when separate particles have the same
wavefunction. In essence, these particles share the same existence.
Entanglement leads to all kinds of bizarre phenomena such as the "spooky action at a
distance" that so puzzled Einstein.
Alicki and Fannes show that when quantum batteries are entangled they become much
better. That's essentially because all the energy from all the batteries can be
extracted at once. "Using entanglement one can in general extract more work per
battery," they say.
In fact, as the number of entangled batteries increases, the performance becomes
arbitrarily close to the thermodynamic limit. In other words, a battery consisting of
large numbers of entangled quantum batteries could be almost perfect.
That's a fascinating result. Quantum batteries in the form of atoms or molecules may be
ubiquitous in nature, in processes such as photosynthesis. Biologists know for example
that during photosynthesis, energy is transferred with 100 per cent efficiency from one
molecular machine to another.
How this happens, nobody knows. Perhaps Alicki and Fannes' work can throw some light on
this process.
However, it's worth pointing out some of the limitations of this work. It is highly
theoretical and does not take into account various practical limitations that are likely
to crop up.
Indeed they acknowledge this and say an interesting goal for the future will be to work
out how practical limitations might change their result.
In the meantime, nanotechnologists can dream about the possibility of exploiting near
perfect batteries in micromachines of the future and learning more about the way nature
may have already perfected this trick.
Ref: http://arxiv.org/abs/1211.1209: Extractable Work From Ensembles of Quantum
Batteries. Entanglement Helps.
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