Photovoltaic systems to work at much lower energies

In summary, photovoltaic technology works by creating a permanent electric field through the depletion of phosphorus and boron doped silicon. This field separates holes and electrons generated by incoming photons and creates an additional electric potential difference. It is not possible to reduce entropy and extract energy from low-energy thermal fluctuations, violating the second law of thermodynamics. The proposed device, which involves using a charged block of boron-doped silicon and a thin insulating layer to create an electric field and separate charges, would not work due to the conservation of energy and the inability to reduce the average kinetic energy of particles. Therefore, it is not possible to extract energy from heat using this method.
  • #1
Edi
177
1
Ordinary photovoltaics work by depleting phosphorus un boron doped silicon in eatch other and creating a permenant electric field, which then separates any pair of hole and electron induced to the conducting band by a incoming photon, creating an aditional elekctric potential difference, which can discharge only trough an external circuit. Right, close, correct?

Ok, so, from what i have been told and understand, the electrons in a phosphorus doped silicon crystal are, at room temperature (even lower, but how much lower?) or higher, are close to or already at the conduction band energy level (as the so called "free electrons", swimming from atom to atom..). That is, effectively, that low energy photons, room temperature kinetic enerby is enough to rise them to the conduction band (?)
So, why deplete the doped silicon to throw the electrons in lower energies, when we could leave them at high energy and, potentially, generating usable electric energy from low level temperature, IR and even room temperature itself?

How to do that? Well, I want to ask about one arrangement here I thought up.
Simply, charge the boron doped silicon from another source of electrons, instead of connecting it to the phosphorus doped silicon, creating a negatively charged block of sklicon. Now, just take the charged block and connecg it to the phosphorus doped silicon with a thin, isolating layer betwene them (or, maybe, even without isolating layer?) --- would theelectric field from charged block be enough to sepparate the hole from electron (push away electrons and attract holes) doing kinda the same as an ordinary PV cell, but at much lower energies (much more effective and useful)?
 
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  • #2
You cannot violate the second law of thermodynamics, and reduce entropy.
If excitations are so low-energetic that thermal fluctuations are sufficient to generate them, they will fall back again in the same way, in the same rate.
 
  • #3
mfb said:
You cannot violate the second law of thermodynamics, and reduce entropy.
If excitations are so low-energetic that thermal fluctuations are sufficient to generate them, they will fall back again in the same way, in the same rate.

How is it really reducing entropy? Is it reducing it in the whole universe or just the localized field? It is possible to reduce entropy in a localized field while increasing the overall entropy, witch we do all the time. Or, in a closed system, perpetual motion is also possible (not that I am suggesting perpetual motion.)
Why will they fall back? Why won't the electric field push away electrons and attract holes?
 
  • #4
You want to get electricity out of heat, without a colder object to dump energy into, if I understood your post correctly.
 
  • #5
mfb said:
You want to get electricity out of heat, without a colder object to dump energy into, if I understood your post correctly.

Well, sort of. Actually, there is no such thing as uniform heat, practically and there is always some heat/ energy difference.. But, yes. Out of heat itself, out of IR radiation.
Can you explain me how and why this setup would not work?
 
  • #6
It would violate the second law of thermodynamics. The most appropriate description here is probably this:
It is impossible, by means of inanimate material agency, to derive mechanical effect from any portion of matter by cooling it below the temperature of the coldest of the surrounding objects.
This applies to electric energy as well.
 
  • #7
Ok, you quote me the law, but what exactly in the scenario prevents it from happening? Not that there is a policeman standing, who says: "you shall not work!"
I want to know the "why?"

.. and, by the way, when I red that law you quoted, it suggested even more that the scenario could work - because temperature temperature we measure is only the average and in practically any system there are some particles moving faster than others and some moving much slower than average, so .. why can't it be cooled to the point of the coolest/ slowest moving particle?
 
  • #8
but what exactly in the scenario prevents it from happening?
As I don't understand how your device is supposed to work, I don't know. And the nice thing of conservation laws: I don't have to know.
It looks like you use an external power supply to separate charges. This won't give electricity, it needs electrocity and heats the object.

because temperature temperature we measure is only the average and in practically any system there are some particles moving faster than others and some moving much slower than average
That is not how temperature works. There is no temperature of individual particles.
 
  • #9
mfb said:
As I don't understand how your device is supposed to work, I don't know. And the nice thing of conservation laws: I don't have to know.
It looks like you use an external power supply to separate charges. This won't give electricity, it needs electrocity and heats the object.

That is not how temperature works. There is no temperature of individual particles.

mm, no, it is said in my first post about the charge that separates the electron form hole - in a normal PV cell there are boron-doped part of silicon that is negative and phosphorus-doped part that is positive (as one takes electrons from the other), but in this case there would be a previously charged boron-doped silicon and another, un-charged, "normal" part of silicon, separated by an insulator, if necessary.

Yes, there is no temperature of individual particles, but there is kinetic energy for individual particle. The average kinetic energy of the particles is what we feel as heat. Of course I know that.
 
  • #10
Well, you cannot reduce this average kinetic energy in your device - therefore, you cannot extract energy out of the heat.
 
  • #11
mfb said:
Well, you cannot reduce this average kinetic energy in your device - therefore, you cannot extract energy out of the heat.

Well, if I put it in a box with uniform temperature and close the circuit - I will get a colder side and a hotter side, but the average temperature in the box will be the same :D
Yes, here comes the entropy law, but that does not really explain anything. It just says: "No!"
 
  • #12
Edi said:
Well, if I put it in a box with uniform temperature and close the circuit - I will get a colder side and a hotter side
That is impossible.
Yes, here comes the entropy law, but that does not really explain anything. It just says: "No!"
Indeed, and that is the most general statement you can do here. A detailed analysis of your setup (by someone who understands it) will eventually show where it does not work as intended.
 

1. How do photovoltaic systems work at lower energies?

Photovoltaic systems work by converting the energy from sunlight into electricity. At lower energies, the photovoltaic cells are still able to absorb and convert the sunlight into usable electricity, though at a lower efficiency.

2. Why is it important for photovoltaic systems to work at lower energies?

Lower energy sunlight is still abundant and can be found in places where traditional solar panels may not be feasible, such as in shaded areas or during cloudy days. Being able to use lower energy sunlight allows for more widespread use of photovoltaic systems.

3. How do photovoltaic systems handle variations in energy levels?

Most photovoltaic systems are designed with built-in regulators and controllers that can adjust and adapt to varying levels of sunlight. This ensures that the system can still produce usable electricity even when the energy levels are not as high.

4. What are the limitations of photovoltaic systems at lower energies?

The main limitation of photovoltaic systems at lower energies is their lower efficiency compared to traditional solar panels. This means that more surface area is needed to produce the same amount of electricity, making them less practical for smaller spaces.

5. How can we improve the efficiency of photovoltaic systems at lower energies?

There are ongoing research and development efforts to improve the efficiency of photovoltaic systems at lower energies. This includes using new materials and technologies, such as perovskite solar cells, that have shown promise in increasing efficiency even at lower energy levels.

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