Solar panel effectiveness

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  • #1
The Baron
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Okay, so i have an idea involving solar panels, and how to improve their effectiveness.
But to verify it I need to know how to calculate the solar panel efficiency, without knowing the solar panel outut. or how to calculate the solar panel output on an electron level. Meaning not regular solar panels but in general if there is a formula for doing that, it would help me tremendously. thank you.
 

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  • #2
phyzguy
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Okay, so i have an idea involving solar panels, and how to improve their effectiveness.
But to verify it I need to know how to calculate the solar panel efficiency, without knowing the solar panel outut. or how to calculate the solar panel output on an electron level. Meaning not regular solar panels but in general if there is a formula for doing that, it would help me tremendously. thank you.
Your question is not very clear. We usually calculate the efficiency of solar panels as the electrical energy output divided by the solar energy input. For current solar panels, this is usually in the 15-20% range. What do you mean by "output on an electron level"? There is also what is called the quantum efficiency, which is the number of electrons out divided by the number of photons in. This is usually higher, and can be 80% or more. Is this what you mean?
 
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  • #3
sophiecentaur
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It surprises me that there don't appear to be 'dual technology' solar panels which could use circulating water as a coolant for the PV panels and to use that in a secondary thermal system. Water plumbing is not as convenient as electric cables but a lot of kWh would be available.
There has to be a no brainer answer for this.
 
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  • #4
hmmm27
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It surprises me that there don't appear to be 'dual technology' solar panels which could use circulating water as a coolant for the PV panels and to use that in a secondary thermal system. Water plumbing is not as convenient as electric cables but a lot of kWh would be available.
There has to be a no brainer answer for this.
Solar cell efficiency starts dropping off at 30C ; perhaps it's considered too low-grade.
 
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  • #5
sophiecentaur
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Solar cell efficiency starts dropping off at 30C
Right: no brainer.
 
  • #6
hmmm27
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Right: no brainer.
There was a company - sorry, couldn't find the link - that was making (or at least promoting) vacuum solar tubes, that did both thermal and PV. Seems sensible ; sometimes one would be preferable.
 
  • #7
DaveE
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It surprises me that there don't appear to be 'dual technology' solar panels which could use circulating water as a coolant for the PV panels and to use that in a secondary thermal system. Water plumbing is not as convenient as electric cables but a lot of kWh would be available.
There has to be a no brainer answer for this.
I think it's just cost and market size. Normal solar panels don't need water cooling, even if it might help. Adding some black pipes on another part of the roof is really cheap and you can allow that water to get pretty hot, unlike efficient PV temperatures. I think the efficiency argument that wins the day is watts/$ installed, in the real world.
 
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  • #8
Baluncore
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Okay, so i have an idea involving solar panels, and how to improve their effectiveness.
It is important not to confuse two similar exciting concepts, learning about an existing field, with the original discovery of that field.

The fact that you have not yet described your idea suggests that you are new to the field. If the idea is worth a million dollars and must remain “commercial in confidence”, then you need to realize that “ideas are ten a penny”. It is close to certain that your idea has been contemplated and evaluated over ten thousand times before.

It is very inefficient when someone new to a field, holding their cards close to their chest, takes control and indirectly cross-examines experts, while trying to learn enough to understand and realize that their flash of an idea was hollow all the time.

If you are really bright you will have many more commercial ideas, so you should do an experiment now, lay your cards on the table and describe your idea up front.
 
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  • #9
Nugatory
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If you are really bright you will have many more commercial ideas, so you should do an experiment now, lay your cards on the table and describe your idea up front.
There’s even a standard way of doing that while protecting the idea: apply for a patent.

If the patent is granted no one else can use the idea without permission so the inventor can work freely and openly to bring it to market.
If the application is rejected the reason will be interesting, one way or anothe: someone else has already had the idea, or it is already well known in the industry, or the inventor hasn’t been clear about exactly what they think they’ve invented.

A patent application is not free, but the cost is negligible compared with financial returns from a successful invention. The non-zero cost encourages people to do their homework and cuts down on the number of half-baked ideas in the system.
 
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  • #10
Baluncore
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A patent application is not free, but the cost is negligible compared with financial returns from a successful invention.
@The Baron I would expect patent costs to be from US$20k to $50k.

If someone disputes your patent you must abandon it, or match them dollar for dollar in the courts while they break you financially. China will simply ignore your patent.

Alternatively, you can publish your idea anywhere, even here on PF. By publishing you prevent anyone else patenting it, so you can still use it. You might even become famous for inventing the technique.
 
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  • #11
sophiecentaur
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Alternatively, you can publish your idea anywhere, even here on PF.
Your name could be worth a lot to someone if the idea is really worth while and marketable. But you are up there with the big boys and improvements on PV, at this stage, will be very much incremental. They need a lot of development money; do you have it?
 
  • #12
The Baron
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Your question is not very clear. We usually calculate the efficiency of solar panels as the electrical energy output divided by the solar energy input. For current solar panels, this is usually in the 15-20% range. What do you mean by "output on an electron level"? There is also what is called the quantum efficiency, which is the number of electrons out divided by the number of photons in. This is usually higher, and can be 80% or more. Is this what you mean?
No, i meant how do you calculate the output of the solar panel, without knowing its efficiency?
 
  • #13
Baluncore
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No, i meant how do you calculate the output of the solar panel, without knowing its efficiency?
You can calculate the output only if you know the input energy and the efficiency.
What information is available ?
 
  • #14
phyzguy
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No, i meant how do you calculate the output of the solar panel, without knowing its efficiency?
As @Baluncore said, you don't. If you don't know the efficiency, you don't know how much energy it will output. Like I said, most solar panels have efficiencies between 15% and 20%. So a reasonable estimate is to do the following: Energy per square meter per day = 1kw/m^2 * 0.15 * 5 hr/day = 0.75 kilowatt-hours/ square meter / day. A typical panel is about 1.65 m^2, so a reasonable estimate is about 1.2 kilowatt-hours per day per panel. Of course this depends on where you are, how much the sun shines, what time of year it is, etc.
 
  • #15
DaveE
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I find it odd that the unknown that you want to calculate is the output power. That's just about the easiest thing to actually measure in normal circumstances.
 
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  • #16
Baluncore
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Unless @The Baron can place all his cards on the table this is going to be a very long, frustrating and drawn out useless thread.
 
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  • #17
irk
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It surprises me that there don't appear to be 'dual technology' solar panels which could use circulating water as a coolant for the PV panels and to use that in a secondary thermal system. Water plumbing is not as convenient as electric cables but a lot of kWh would be available.
There has to be a no brainer answer for this.

There are PVT (Photovoltaic+Thermal) panels available (just search). These are obviously (significantly) more expensive than PV panels. PVT system should be properly designed: To cool PV panels one has to take out all heat out of them, from typical panel array one would get much more heat than needed for a household what to do with the excess heat? There should be thus combination of several PVT and more PV panels in such system. But then the PV panels would not be cooled and the claimed 10% increased production of electricity in cooled panels would not be realized.
 
  • #18
sophiecentaur
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Large tanks of water make useful stores of energy for heating. You can store many kWh of energy in a tonne of hot water overnight or longer. Mainly suitable for new builds, though.
If there is danger of PV over heating then what’s wrong with a simple radiator system or even evaporative cooling?
 
  • #19
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Solar cell efficiency is at the moment capped at a theoretical 30% maximum. State of the art is around 25%. I think you would be better off trying to increase that theoretical max.
 
  • #20
berkeman
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Solar cell efficiency is at the moment capped at a theoretical 30% maximum. State of the art is around 25%. I think you would be better off trying to increase that theoretical max.
Sounds about right, but it's always best to post a link to the source when making statements like that at PF. :smile:
 
  • #21
Mayhem
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Sounds about right, but it's always best to post a link to the source when making statements like that at PF. :smile:
I have the information from Ph.D. students and researchers actively working on solar cells, but I guess "word of mouth" isn't really a valid citation.
 
  • #22
willem2
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Solar cell efficiency is at the moment capped at a theoretical 30% maximum. State of the art is around 25%. I think you would be better off trying to increase that theoretical max.
I think you mean the Shockley Queisser Limit?
https://en.wikipedia.org/wiki/Shockley–Queisser_limit.
This is only a limit for cells made up of PN junctions made from a single material with a single bandgap. All incoming photons with less than the bandgap energy are wasted, and any photons with more than the bandgap energy will waste the extra energy. This comes out to about 33% max, for a bandgap from 1.2 to 1.5 V (You need a detailed calculation, as it depends on the solar spectrum)

You can however go beyond that with multijunction cells. made from different semiconductors and with PN junctions with different bandgap Energy layered on top of each other.
 
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  • #23
Mayhem
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I think you mean the Shockley Queisser Limit?
https://en.wikipedia.org/wiki/Shockley–Queisser_limit.
This is only a limit for cells made up of PN junctions made from a single material with a single bandgap. All incoming photons with less than the bandgap energy are wasted, and any photons with more than the bandgap energy will waste the extra energy. This comes out to about 33% max, for a bandgap from 1.2 to 1.5 V (You need a detailed calculation, as it depends on the solar spectrum)

You can however go beyond that with multijunction cells. made from different semiconductors and with PN junctions with different bandgap Energy layered on top of each other.
Yes, I read up on it, and multijunction cells seem very promising.
 
  • #24
irk
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Large tanks of water make useful stores of energy for heating. You can store many kWh of energy in a tonne of hot water overnight or longer. Mainly suitable for new builds, though.
If there is danger of PV over heating then what’s wrong with a simple radiator system or even evaporative cooling?
Sure, storage of heat in tanks is used in Solar Thermal. The problem is where the heat is to be used and how much of it is needed. Unfortunately most heat will be produced during the summer when there is no need for heating. From this reason Solar Thermal is used mostly for hot water needs in households, together with storage water tank. The amount of heat needed for this can be supplied by several thermal panels. But in PV installations the number of panels is typically bigger than several.

Then of course one could use PVT panels with cooling them to produce more electricity. But that is not worth trouble since PV output is reduced by 10-15% in hot conditions and that can be compensated by adding 1-2 PV panels which is way simpler and cheaper than buliding cooling system. Besides, cooling system with radiator or evaporation will emit heat somewhere around house and especially during hot summer.

In the end, people who want solar thermal make separate system using thermal panels for hot water and PV panels for electricity.

That said, there is thermal panel technology using underground aquifer ore boreholes for storing significant amount of heat during the summer and recovering it during winter. But that is entirely different game if one considers issues and expense of buliding underground heat storage installation with megawatthours capacity.
 
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  • #25
sophiecentaur
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That said, there is thermal panel technology using underground aquifer ore boreholes for storing significant amount of heat during the summer and recovering it during winter. But that is entirely different game if one considers issues and expense of buliding underground heat storage installation with megawatthours capacity.
Cool!
 
  • #26
The Baron
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You can calculate the output only if you know the input energy and the efficiency.
What information is available ?
I'm not sure whether my understanding of how solar panels work is correct, but I assume that they work because of the photoelectric effect, I thought maybe If I could calculate the number of photons that hit the metal and the maximum kinetic energy they give the electrons, I could know the amount of electricity produced. I'm just very uncertain about whether my idea is correct.
 
  • #27
sophiecentaur
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photons that hit the metal and the maximum kinetic energy they give the electrons
PV panels are solid state and the range of photon energies that actually produce the electrical energy is limited. The probability that an incident photon will release an electron (photon efficiency) will depend (as mentioned higher up) on the characteristics of the PN junction. Photons with energy outside the range are 'wasted' - they don't just give a higher voltage, for instance.
 
  • #28
bob012345
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I'm not sure whether my understanding of how solar panels work is correct, but I assume that they work because of the photoelectric effect, I thought maybe If I could calculate the number of photons that hit the metal and the maximum kinetic energy they give the electrons, I could know the amount of electricity produced. I'm just very uncertain about whether my idea is correct.
I suggest you hit the library and get a book on solar energy that includes a little bit of semiconductor knowledge. I recommend the following book you might find at your local library or you can just buy it

https://www.amazon.com/dp/1906860327/?tag=pfamazon01-20
 
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  • #29
bob012345
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Yes, I read up on it, and multijunction cells seem very promising.
My long term bet is on direct conversion of sunlight to power through optical rectennas.
 
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