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The efficiency of photovoltaic cells is surprisingly strong function of junction temperature. Hotter usually means lower efficiency. If one searches for example for images and sites tagged with "floatovoltaics" it's clear that some effort is being made to use water to cool the junctions to maintain efficiency under maxiumum solar incident flux. I think it's because the higher temperature allows more random recombination within the junction, before the charge can be collected. Any incident solar radiation that is not converted to electrical power (i.e. most of it) will heat the cells.

Are photovoltaics in spacecraft just 'hanging there' at whatever equilibrium temperature they happen to attain, or is the temperature sometimes actively controlled or at least limited in some way? Can they ever get too cold?

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above: Image from Renewable Energy World which it credits to Far Niente, a Napa Valley winery.

Floatovoltaics from NGEO from Kyocera

above: Image from National Geographic which it credits to Kyocera, Inc.

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above: Image from an article with many flotovoltaic photos in pv-magazine which it credits to New Jersey American Water

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above: Image from an article *with many flotovoltaic photos in pv-magazine which it credits SGP Solar.

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The only solar cell temperature sensitive mission I could think of was MESSERGER. The mission to Mercury had solar panels that were 2/3 mirror surfaces, and they were programmed to rotate away from the Sun/Mercury to reduce incoming light if the temperature rose too high. This was allowable because the panels produced more power in Mercury orbit than the mission required.

Source. See page 27.

If you want to look at other missions and see what they did, wikipedia has a great list of the two missions to Mercury and the numerous missions to Venus. These are some of my favorite missions since they are so extreme. I especially like Venera 9, which took the first photos from the surface of another planet (So cool!).

Decreasing temperature from room temperature increases efficiency until somewhere below 100 K. Below this temperature the efficiency drops off as the short circuit current decreased. Semiconductor physics is complicated (citation needed), so I glossed over the reasons why this happens.

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  • $\begingroup$ Actually, all of the orbiter missions to Mercury and Venus had this temperature problem to a degree (groan...). This one was in my head at the moment and I didn't think to look at others. $\endgroup$ – Andrew W. Jul 22 '16 at 1:18
  • $\begingroup$ Great! I never would have thought of it! If you just add the names of a few more to the question that would be great! $\endgroup$ – uhoh Jul 22 '16 at 1:21
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    $\begingroup$ I added the whole list of both planets. Have fun :D $\endgroup$ – Andrew W. Jul 22 '16 at 21:32
  • $\begingroup$ I think the abstract is open and visible here: http://www.sciencedirect.com/science/article/pii/S1876610213000829. For some reason I think this sentence is applicable :) "However, regions with high altitude have higher performance ratios due to low temperature, like, southern Andes, Himalaya region, and Antarctica." $\endgroup$ – uhoh Jul 25 '16 at 9:46
  • $\begingroup$ Actually the whole paper is now viewable there and the PDF can be saved as well. $\endgroup$ – uhoh Apr 10 '18 at 2:49
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I just came across this, after reading this interesting question. The Solar Probe Plus mentioned there will have (very) actively cooled photovoltaics on special articulated mountings. It is planned to pass within nine solar radii of the sun's surface (about 4 million miles!) Yikes!

It is further described in this answer.

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above: screen shot from NASA's Solar Probe Plus Fact Sheet

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above: illustration of NASA's Solar Probe Plus from here. Sun is up - to state the obvious!

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