

IBM’s solar tech is 80% efficient thanks to supercomputer cooling tech - wittyphrasehere
http://arstechnica.com/science/2013/04/ibms-solar-tech-is-80-efficient-thanks-to-supercomputer-know-how/

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comicjk
This is the problem with stating efficiency in terms of energy instead of
exergy (work). Capturing the low-temperature waste heat of the solar panels is
not comparable to capturing the same amount of energy as electricity. It's a
good technology if it can be made inexpensive, but calling it "80% efficient
solar" is quite misleading.

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jmount
My read of the article agrees with you: they are claiming the removal of the
waste heat as "efficiency" without taking into account the efficiency of using
the waste heat. I was hoping they would claim better cooling made the PV cell
more efficient (I know, a silly claim- but by analogy that larger temperature
differences make more efficient heat engines). And there may in fact be no use
at all for the waste heat (who needs waste heat in the Sahara?).

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comicjk
In fact cooling solar cells does make them more efficient. It's just that the
effect is small because the "high" temperature is already so high (the
temperature of the incoming photons is effectively that of the surface of the
sun). A Carnot engine working between 330K and 5800K, ie a reversible solar
cell, would be 95% efficient. If the cell's temperature were dropped to 300K
it would be 94%. So we can estimate the efficiency change for a 30 Celcius
cooling of the cell at 1%.

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tedsanders
Your comment seems to imply that the main problem with temperature is
radiative recombination. Is that the case? I thought heat caused other non-
ideal problems.

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comicjk
True, it will also increase internal resistance. I'm more of a thermo guy,
though, so I can't estimate the remainder.

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ttrreeww
Misleading, they heat the water but does not convert it to electricity (which
would lead to further losses)

