The Naked Scientists
  • Login
  • Register
  • Podcasts
      • The Naked Scientists
      • eLife
      • Naked Genetics
      • Naked Astronomy
      • In short
      • Naked Neuroscience
      • Ask! The Naked Scientists
      • Question of the Week
      • Archive
      • Video
      • SUBSCRIBE to our Podcasts
  • Articles
      • Science News
      • Features
      • Interviews
      • Answers to Science Questions
  • Get Naked
      • Donate
      • Do an Experiment
      • Science Forum
      • Ask a Question
  • About
      • Meet the team
      • Our Sponsors
      • Site Map
      • Contact us

User menu

  • Login
  • Register
  • Home
  • Help
  • Search
  • Tags
  • Member Map
  • Recent Topics
  • Login
  • Register
  1. Naked Science Forum
  2. Non Life Sciences
  3. Physics, Astronomy & Cosmology
  4. How is photon number related to wattage of a solar panel?
« previous next »
  • Print
Pages: [1] 2   Go Down

How is photon number related to wattage of a solar panel?

  • 27 Replies
  • 12561 Views
  • 0 Tags

0 Members and 1 Guest are viewing this topic.

This topic contains a post which is marked as Best Answer. Press here if you would like to see it.

Terry McHugh

  • Guest
How is photon number related to wattage of a solar panel?
« on: 28/11/2011 15:30:02 »
Terry McHugh  asked the Naked Scientists:
   
A question that I cannot find an answer to and which I believe is currently relevant refers to solar PV panels.

Light (photons) strike a solar PV panel which, for a given size emits watts. 

How can the light striking the panel be measured  against the wattage output.  (X photons in = Y watts out) What is the correlation between these two factors.

Regards

Terry

What do you think?
« Last Edit: 28/11/2011 15:30:02 by _system »
Logged
 



Offline syhprum

  • Naked Science Forum King!
  • ******
  • 5093
  • Activity:
    10.5%
  • Thanked: 64 times
    • View Profile
How is photon number related to wattage of a solar panel?
« Reply #1 on: 28/11/2011 18:46:24 »
You cannot directly equate photons with Watts there is a time element involved, Photons are carriers of energy measured in Joules while Watts are units in which the rate of flow of energy is measured i.e 1 Watt = 1 Joule per second.
You must talk of Photons per second or energy accumulated in units such as KWh (3,600,000 Joules) 
If you are interested in solar panels The figures are that Solar Photons are assumed to carry 1.1 Ev which converts to 1.76 * 10^-19 Joules while the typical efficiency of a solar panel would be 15% while the incident energy in sunlight at ground level is quoted as 1KW per meter^2.
Logged
syhprum
 

Offline acsinuk

  • Sr. Member
  • ****
  • 431
  • Activity:
    4.5%
  • Thanked: 6 times
    • View Profile
    • electricmagnofluxuniverse.blogspot.com
How is photon number related to wattage of a solar panel?
« Reply #2 on: 04/12/2011 03:13:08 »
Why not simplify the maths and ask how many photons of white light [ whose frequency average is say 6 *10^14 ] would be required to give a magnetic flux output of 1 watt per second.
Answer is I think 1.76*10^19/6*10^14 = 3*10^4
So it takes about 30 thousand photons hitting a one square metre solar panel per second at right angles to produce 1 Watt of energy at 100% efficiency. You would need 1000 wattsecs for a kW at typically 20% efficiency then you would need 5 times as many making it 1.5*10^8 photons!  Someone should check the maths to confirm the figures.
CliveS
Logged
A.C.Stevens
 

Offline syhprum

  • Naked Science Forum King!
  • ******
  • 5093
  • Activity:
    10.5%
  • Thanked: 64 times
    • View Profile
How is photon number related to wattage of a solar panel?
« Reply #3 on: 04/12/2011 06:41:51 »
"1 Watt of energy at 100% efficiency" ???

I clarified the matter of units without actually doing the detailed arithmetic for the guy and here you are talking abouts Watts as energy.
energy is measured in Joules watts is the measure of how fast energy flows i.e Joules per second.

Logged
syhprum
 

Offline Soul Surfer

  • Naked Science Forum King!
  • ******
  • 3384
  • Activity:
    0%
  • Thanked: 6 times
  • keep banging the rocks together
    • View Profile
    • ian kimber's web workspace
How is photon number related to wattage of a solar panel?
« Reply #4 on: 04/12/2011 11:47:58 »
acsinuk  there are several fundamental errors in your calculation of the number of photons per second required to give an output of one watt (oops! error deleted  [:(!] should have said joule per second) so other people should disregard this very low number that he suggests as it is many orders of magnitude greater than this.

Directly from syhprum's previous answer one typical solar photon equals  1.76 * 10^-19 Joules so you need   1/ (1.76 * 10^-19 ) = around 6*10^18   per second to produce 1 Joule per second of incident power and five times more if the quantum efficiency is only 20%
« Last Edit: 04/12/2011 22:49:27 by Soul Surfer »
Logged
Learn, create, test and tell
evolution rules in all things
God says so!
 



Offline Bored chemist

  • Naked Science Forum GOD!
  • *******
  • 21923
  • Activity:
    100%
  • Thanked: 508 times
    • View Profile
How is photon number related to wattage of a solar panel?
« Reply #5 on: 04/12/2011 15:35:41 »
Watt is it about units? ;-)
"number of photons per second required to give an output of one watt per second "



Logged
Please disregard all previous signatures.
 

Offline Geezer

  • Naked Science Forum King!
  • ******
  • 8314
  • Activity:
    0%
  • Thanked: 7 times
  • "Vive la résistance!"
    • View Profile
How is photon number related to wattage of a solar panel?
« Reply #6 on: 04/12/2011 18:32:07 »
Quote from: Bored chemist on 04/12/2011 15:35:41
Watt is it about units? ;-)
"number of photons per second required to give an output of one watt per second "


Maybe the joules are multiplying? That would solve our energy problems PDQ.
Logged
There ain'ta no sanity clause, and there ain'ta no centrifugal force æther.
 

Marked as best answer by on 22/02/2021 22:42:26

Offline syhprum

  • Naked Science Forum King!
  • ******
  • 5093
  • Activity:
    10.5%
  • Thanked: 64 times
    • View Profile
  • Undo Best Answer
  • How is photon number related to wattage of a solar panel?
    « Reply #7 on: 04/12/2011 20:13:14 »
    What a strange mistake from a scientifically trained correspondent "one watt per second" this can only be the rate at which the power is changing !!!
    Logged
    syhprum
     

    Offline Soul Surfer

    • Naked Science Forum King!
    • ******
    • 3384
    • Activity:
      0%
    • Thanked: 6 times
    • keep banging the rocks together
      • View Profile
      • ian kimber's web workspace
    How is photon number related to wattage of a solar panel?
    « Reply #8 on: 04/12/2011 22:52:22 »
    syhprum that's what comes of doing things too quickly and working in mixed units  I have now corrected my error  thanks for pointing it out   [:)]
    Logged
    Learn, create, test and tell
    evolution rules in all things
    God says so!
     



    Offline Geezer

    • Naked Science Forum King!
    • ******
    • 8314
    • Activity:
      0%
    • Thanked: 7 times
    • "Vive la résistance!"
      • View Profile
    How is photon number related to wattage of a solar panel?
    « Reply #9 on: 05/12/2011 00:00:48 »
    I knew we should have stuck with BTUs/month.
    Logged
    There ain'ta no sanity clause, and there ain'ta no centrifugal force æther.
     

    Offline Soul Surfer

    • Naked Science Forum King!
    • ******
    • 3384
    • Activity:
      0%
    • Thanked: 6 times
    • keep banging the rocks together
      • View Profile
      • ian kimber's web workspace
    How is photon number related to wattage of a solar panel?
    « Reply #10 on: 05/12/2011 08:36:53 »
    An interesting point geezer!  A bit off topic but Have you tried to understand the relationship between the numbers in your gas meter and your gas bill.  It is way beyond most experts in quantum physics and relativity.   [:D]
    Logged
    Learn, create, test and tell
    evolution rules in all things
    God says so!
     

    Offline syhprum

    • Naked Science Forum King!
    • ******
    • 5093
    • Activity:
      10.5%
    • Thanked: 64 times
      • View Profile
    How is photon number related to wattage of a solar panel?
    « Reply #11 on: 05/12/2011 13:45:41 »
    Early gas meters had alternate dials reading clockwise and anti clockwise making it very tricky to read.

    Geezer
    I think we should abandon foreign units like Joules and use proper Scottish units like Watt seconds.
    Deduct one brownie point I did not realise he came from Salford !!
    « Last Edit: 05/12/2011 13:50:02 by syhprum »
    Logged
    syhprum
     

    Offline Geezer

    • Naked Science Forum King!
    • ******
    • 8314
    • Activity:
      0%
    • Thanked: 7 times
    • "Vive la résistance!"
      • View Profile
    How is photon number related to wattage of a solar panel?
    « Reply #12 on: 05/12/2011 19:51:48 »
    Our gas is liquid propane pumped in US gallons from a tanker truck. They know when to deliver it based on the average daily temperatures. We never have to call them.

    I seem to remember the UK gas bill referred to therms, but I would assume the units are a bit more SI these days?

    I think the air conditioning folks in the US still use BTUs. They also rate AC units in "tons". It took me a while to figure out what on earth they were on about.
    Logged
    There ain'ta no sanity clause, and there ain'ta no centrifugal force æther.
     



    Offline damocles

    • Hero Member
    • *****
    • 756
    • Activity:
      0%
    • Thanked: 1 times
      • View Profile
    How is photon number related to wattage of a solar panel?
    « Reply #13 on: 05/12/2011 20:13:31 »
    Quote from: Geezer on 05/12/2011 19:51:48
    (...snip...)
    I think the air conditioning folks in the US still use BTUs. They also rate AC units in "tons". It took me a while to figure out what on earth they were on about.

    1 ton = 1019 kg
    speed of light in vacuum = 2.998E8 m/s

    E=mc2 = 9.0E19 J

    No wonder the electricity grid struggles on hot days!

    [;)]
    Logged
    1 4 6 4 1
    4 4 9 4 4     
    a perfect perfect square square
    6 9 6 9 6
    4 4 9 4 4
    1 4 6 4 1
     

    Offline Geezer

    • Naked Science Forum King!
    • ******
    • 8314
    • Activity:
      0%
    • Thanked: 7 times
    • "Vive la résistance!"
      • View Profile
    How is photon number related to wattage of a solar panel?
    « Reply #14 on: 05/12/2011 20:25:10 »
    Quote from: damocles on 05/12/2011 20:13:31
    1 ton = 1019 kg
    speed of light in vacuum = 2.998E8 m/s

    E=mc2 = 9.0E19 J

    No wonder the electricity grid struggles on hot days!

    [;)]

    Gotcha!

    "Air conditioner equipment power in the U.S. is often described in terms of "tons of refrigeration". A ton of refrigeration is approximately equal to the cooling power of one short ton (2000 pounds or 907 kilograms) of ice melting in a 24-hour period. The value is defined as 12,000 BTU per hour, or 3517 watts.[10] Residential central air systems are usually from 1 to 5 tons (3 to 20 kilowatts (kW)) in capacity."

    http://en.wikipedia.org/wiki/Air_conditioner

    Logged
    There ain'ta no sanity clause, and there ain'ta no centrifugal force æther.
     

    Offline Bored chemist

    • Naked Science Forum GOD!
    • *******
    • 21923
    • Activity:
      100%
    • Thanked: 508 times
      • View Profile
    How is photon number related to wattage of a solar panel?
    « Reply #15 on: 05/12/2011 21:06:42 »
    That may well take over from the barn yard atmosphere as my favourite "ridiculous unit".
    The clo gives it a run for its money.
    Anyway the answer to the original question is something like 3X 10^ 19 photons of visible light per second for each Watt of power output.

    Who is counting?
    Logged
    Please disregard all previous signatures.
     

    Offline syhprum

    • Naked Science Forum King!
    • ******
    • 5093
    • Activity:
      10.5%
    • Thanked: 64 times
      • View Profile
    How is photon number related to wattage of a solar panel?
    « Reply #16 on: 05/12/2011 21:36:34 »
    Don't atom bashing physicist's talk about effective cross sectional area in barns
    Logged
    syhprum
     



    Offline Geezer

    • Naked Science Forum King!
    • ******
    • 8314
    • Activity:
      0%
    • Thanked: 7 times
    • "Vive la résistance!"
      • View Profile
    How is photon number related to wattage of a solar panel?
    « Reply #17 on: 05/12/2011 22:12:12 »
    Quote from: Bored chemist on 05/12/2011 21:06:42
    That may well take over from the barn yard atmosphere as my favourite "ridiculous unit".

    It does seem a bit bizarre, but I just realized it might have a very practical origin. The US railroads shipped vast quantities of perishable produce in "reefers" - refrigerated box cars. The early versions had ice loaded through their roofs at stops along the way. It was probably important to know how many tons of ice should be loaded into each car for the next part of the journey.
    Logged
    There ain'ta no sanity clause, and there ain'ta no centrifugal force æther.
     

    Offline syhprum

    • Naked Science Forum King!
    • ******
    • 5093
    • Activity:
      10.5%
    • Thanked: 64 times
      • View Profile
    How is photon number related to wattage of a solar panel?
    « Reply #18 on: 05/12/2011 22:16:23 »
    http://en.wikipedia.org/wiki/List_of_unusual_units_of_measurement

    Wikipedia has a fine collection of odd units, some in genuine use and other just a farce.
    One of the oddests still in common use is "horse power" 746 watts.
    « Last Edit: 05/12/2011 22:22:53 by syhprum »
    Logged
    syhprum
     

    Offline damocles

    • Hero Member
    • *****
    • 756
    • Activity:
      0%
    • Thanked: 1 times
      • View Profile
    How is photon number related to wattage of a solar panel?
    « Reply #19 on: 05/12/2011 23:49:09 »
    The barn is a cross-sectional area unit of 1.0E-28 m2
    It is very much on the scale of an atomic nucleus; nuclear collision cross-sections range between about one thousandth and one thousand barn.

    You can find it fairly easily in wikipedia.

    What you may not find, and I cannot reference (knowing it only through my 1960s Physics lecturer and a few particle physicists of my acquaintance from the late 60s and early 70s) is that it was whimsically named after the size of barn door that would need to be closed to prevent a nucleus from straying.
    Logged
    1 4 6 4 1
    4 4 9 4 4     
    a perfect perfect square square
    6 9 6 9 6
    4 4 9 4 4
    1 4 6 4 1
     



    • Print
    Pages: [1] 2   Go Up
    « previous next »
    Tags:
     

    Similar topics (5)

    Is there a "photon boundary"?

    Started by GeezerBoard Physics, Astronomy & Cosmology

    Replies: 14
    Views: 7292
    Last post 22/09/2010 11:40:15
    by yor_on
    Will a photon clock run at a different rate from an atomic clock under gravity?

    Started by amritBoard Physics, Astronomy & Cosmology

    Replies: 147
    Views: 68658
    Last post 07/06/2010 06:43:34
    by Geezer
    Two low energy photons for one high energy photon in fluorescence possible?

    Started by McKayBoard Physics, Astronomy & Cosmology

    Replies: 6
    Views: 3240
    Last post 19/05/2019 13:05:28
    by alancalverd
    Because we have no dark matter planet in our solar system, can we assume that dark matter is not sticking to itself?

    Started by thedocBoard Physics, Astronomy & Cosmology

    Replies: 3
    Views: 3371
    Last post 18/08/2016 02:39:19
    by PmbPhy
    Is solar energy the same as light energy?

    Started by FeliciaBoard Technology

    Replies: 6
    Views: 19679
    Last post 19/03/2020 15:17:27
    by Paul25
    There was an error while thanking
    Thanking...
    • SMF 2.0.15 | SMF © 2017, Simple Machines
      Privacy Policy
      SMFAds for Free Forums
    • Naked Science Forum ©

    Page created in 0.205 seconds with 81 queries.

    • Podcasts
    • Articles
    • Get Naked
    • About
    • Contact us
    • Advertise
    • Privacy Policy
    • Subscribe to newsletter
    • We love feedback

    Follow us

    cambridge_logo_footer.png

    ©The Naked Scientists® 2000–2017 | The Naked Scientists® and Naked Science® are registered trademarks created by Dr Chris Smith. Information presented on this website is the opinion of the individual contributors and does not reflect the general views of the administrators, editors, moderators, sponsors, Cambridge University or the public at large.