Solar cells and entropy

[Anonymous No.9722284]

Lads I got a dumb, but, I hope, fun question.
I don't know much about solar cells physics, I assume it's just "photon goes in, current goes out"

So what if I put a solar cell into a hot black box. Because of black body radiation, some photons of the appropriate wavelength will hit the cell from time to time. Thus we'll get a current.

What the shit happens to entropy there ? I suppose the box should cool down over time because of those absorbed photons. But then we are basicall making temperature into electricity, without using a temperature difference, which violates every law of thermodynamics I can remember.

So where's my mistake ?

[Anonymous No.9722328]

Going off the top of my head, I'd say that your solar cell will equilibriate with the box as it heats up, emitting as many photons as it absorbs, giving no net current. And the entropy "lost" by the black box in converting temperature to current is less that or equal to the entropy gain when you equilibriate the cell and box.

[Anonymous No.9722346]

>>9722328
Ah, so the cell itself would have to be colder than its environment to work. Yeah it makes sense.

[Anonymous No.9723062]

>>9722284
No, the cell has to be warmer than at least part of the environment.
A solar cell is absorbing light from the (hot) sun. The frequency distribution of the light represents a temperature, T1
The cell re-radiates the un-converted energy to its surroundings at temperature T2.
The process cannot be more efficient than a Carnot Cycle operating between T1 and T2.
The solar cell (and life in general) keeps going because the Earth re-radiates its heat into interstellar space, effectively 4 Kelvin.

Another way of looking at it is that the sunlight brings in entropy E/T1 and the Earth loses the same amount of energy (averaged over time. It has to or it would continually grow hotter or cooler) and the re-radiation carries off entropy E/T2.
T2 < T1 (Earth is cooler than the Sun) so we "dispose" of the entropy life produces in the process of becoming more organized. The "creation science" nutjobs ignore this when they claim Life Violates the 2nd Law.

If you're completely surrounded by a black box, you can export electricity (through a wire running out of the box) only until the cell reaches the same temp as the box.

We can put a solar cell in a refrigerator and it will still make electricity (if we gimmick the little light inside to stay on even with the door closed.) The energy input from the light keeps the (well-insulated) cell warmer than the surrounding shelves.