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