# Can plants/solar panels decrease entropy?

If in theory there was a very efficient and powerfull refrigerator.

Is it possible that a plant/solar panel could turn that heat into usuable energy, faster then what the frige uses up?

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russ_watters
Mentor
The sun created a lot of entropy to makee that light, so no.

im not talking about the sun, i mean the refrigerators heat sink becoming hot enough to radiate light that can be converted by the plant/solarcell

davenn
Gold Member
2019 Award
im not talking about the sun, i mean the refrigerators heat sink becoming hot enough to radiate light that can be converted by the plant/solarcell
If my fridge/ freezer was getting that hot that it was emitting light i would be switching it off before it burst into flames. It would have to be seriously faulty

Dave

Drakkith
Staff Emeritus
If in theory there was a very efficient and powerfull refrigerator.

Is it possible that a plant/solar panel could turn that heat into usuable energy, faster then what the frige uses up?
You could build a heat engine that uses the waste heat of a refrigerator to produce power, but it would only be a fraction of what the fridge is using.

russ_watters
Mentor

So its possible for normal light waves to be converted into chemical energy by plants, but not for infra red spectrum? Where is this so called "wavelength" point where suddenly light can or can no longer be converted? Give me a number if possible, and please keep it theoretical.

Drakkith
Staff Emeritus
So its possible for normal light waves to be converted into chemical energy by plants, but not for infra red spectrum? Where is this so called "wavelength" point where suddenly light can or can no longer be converted? Give me a number if possible, and please keep it theoretical.
Not sure why it needs to be kept theoretical, this is a very real thing that happens everyday. But to answer your question, there is no single number for the wavelength that plants simply stop converting. If you were to graph the spectrum that is absorbed by the plant it would taper off gradually as you get to longer and longer wavelengths on the red end. By about 700 nanometers the absorption is "practically zero". This corrosponds with the very far end of the visible spectrum and the start of the "near infrared" section.

If there was a device that could convert heat into chemical/electrical energy at a decent rate, even at "relatively low" temperatures.
The heat would still flow from hot to the colder(device).
But the exact moment a bit of heat is converted into a chemical bond, the temperature difference between the room and the device wil lincrease.
Would that violate the 2nd law of thermal dynamics?

mfb
Mentor
Plants can direct their chemical reactions because they have a source of low-entropy energy (energetic photons, as visible light), and can emit high-entropy energy (heat, for example as infrared photons) - the difference allows them to use some fraction of the energy for photosynthesis.
If you try to use infrared radiation both as input and output, your chemical reactions will always end in some equilibrium and you cannot extract energy.

Thanks for the info about plants, i didnt know exactly how they worked.