Panels giving 140% of Imp ? help!

lazza
lazza Solar Expert Posts: 336 ✭✭✭
A Mystery:

In one of our installations, we've just had a 40A fuse blow in the DC circuit from the panels to the charge controller (Xantrex C40).

There are 6 panels in a 24V system (not MPPT), supposedly of 190W each with Imp of 5.06A. So maximum power should give 31A, hence the 40A fuses.

I replaced the fuse with another 40A fuse, and the system returned to normal functioning. However, when I measured the current coming from the panels.. it measured as much as 42A at one stage, and dropped to 36A. My multimeter has shown itself to be very reliable.

How is this possible? There were some clouds, so i suppose a bit of cloud effect could be possible, but i also measured when there was a clear patch and it measured around 5.7A for each panel, around 34A in total.

Are we in a period of unprecented solar activity?

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Panels giving 140% of Imp ? help!

    Not necessarily.

    Edge-of-cloud effect would account for occasional current spikes, but consistent high output would be due to some other factor. Either the panel data is wrong or the elevation is high (resulting in greater insolation).

    190 Watts with a 5.06 Imp would be a Vmp of 37.5, which is odd. Can you give more info on the panels?
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Panels giving 140% of Imp ? help!

    even reflections from water or even buildings painted white could up the output of the pvs. it could also be that the pvs are outputting more than their stated output as many pvs nowadays have a 0% to +3% or +5%. add in your edge of cloud, your local insolation could be higher than the stc values, and other reflections and it can pop it up. don't forget that fuses are also not that exacting on the point they blow and older fuses can fail out of the blue as well. your pvs should list a value for isc and multiply that by the numbers of parallel pvs, or strings of pvs to be technically correct, and then we here in the states are required to multiply that x1.56.

    now your problem isn't that total output of the paralleled arrangement is blowing a 40a fuse as that is easily remedied. your problem may be the individual pvs or strings need fused to prevent possible damage to any pv that may develop a problem and become the load for the rest of the pvs. odds are the isc is around 5.5a and multiply that by 1.56 and it's 8.58a. being the closest common commercial value of a fuse may be 10a then each pv should have a 10a fuse before the outputs are combined.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Panels giving 140% of Imp ? help!

    For maximum continous current rating of wiring/fuses/breakers, then you should multiply by 1.25x... So 32 amp Imp:

    32 amps * 1.25 NEC factor = 40 amp fuse+breaker rating minimum

    However, for pwm controllers which do not have any method of current control (unlike MPPT controllers which can limit their output to a specified level forever, safely and reliably), your should have another 1.25 safety factor:

    32 amps * 1.25 NEC solar factor * 1.25 NEC wiring factor = 50 amps

    So, if I understand NEC requirements correctly (no guarantee here), then you should be looking at 50 amp wiring/fusing.

    Note, for PWM controllers, cold weather does not materially affect Imp (Imp does drop a very tiny amount with falling temperatures), so this would be purely an edge of cloud/refections from snow, high altitude, water sand sort of event.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: Panels giving 140% of Imp ? help!

    These days most larger panels aren't made in 12 or even 24 volt nominal sizes, wonder if they were mislabeled? What voltage are you seeing from individual panels?, if they have breakers, just disconnect one and take a VOC reading, you could also take a vmp reading at the fuse being popped.

    I take it your measuring the amperage with a clamp meter, did you zero the meter?

    Is this a new setup or has it been in place for a while?
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • lazza
    lazza Solar Expert Posts: 336 ✭✭✭
    Re: Panels giving 140% of Imp ? help!

    HI- in reply to your questions:

    1. Panel is a Bauer 24V 190W (datasheet attached)
    2. I had an extra level of protection: 6 x 10A fuse in positive line of each panel- one of them had semi-melted, so I have replaced them all with 15A fuses. But it was the general 40A fuse that blew. I will be replacing it with a 50A fuse as suggested.

    The only thing that occurs to me is that the installation happens to be right next to a large PV field (the big PV fields that boomed in Spain from 2007 to 2009)... the panels are facing the same direction as the PV field, hence there is no direct reflection, but maybe alot of reflected light is, however, getting to the panels ??

    (i have attached a photo of the installation with the PV field right next to it)Attachment not found.

    Cheers
    Larry
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Panels giving 140% of Imp ? help!

    15a is too high of a value imo. if the 10a fuse partially melted it could be a number of things, but to have more than double the isc for a fuse is not a good idea. if you were to have 3 pvs producing and you disconnected one for whatever reason and reconnected it, but backwards then the output of the other 2 will pump their full outputs into the reversed pv and destroy it. i know you have 6 pvs, but what if some were shaded at the time and it would not be enough to pop a 15a fuse with 2 pvs feeding a reversed pv.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Panels giving 140% of Imp ? help!

    I would disconnect one panel, short it, and watch the Isc through the day. That way you can determine if they are actually producing greater than rated current or if there is perhaps something wrong with the fuses (may not be able to take the Voltage or heat).
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Panels giving 140% of Imp ? help!

    Marc's question about fuse block capabilities is true... Wayne from NS Canada had used automotive fuses+holders and the whole assembly failed in a melted mess and they were not operated anywhere near their rated current. Fortnatually, Wayne had the fuse blocks in a metal box and it saved him from a possible fire.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Panels giving 140% of Imp ? help!
    lazza wrote: »
    A Mystery:

    In one of our installations, we've just had a 40A fuse blow in the DC circuit from the panels to the charge controller (Xantrex C40).

    There are 6 panels in a 24V system (not MPPT), supposedly of 190W each with Imp of 5.06A. So maximum power should give 31A, hence the 40A fuses.

    I replaced the fuse with another 40A fuse, and the system returned to normal functioning. However, when I measured the current coming from the panels.. it measured as much as 42A at one stage, and dropped to 36A. My multimeter has shown itself to be very reliable.

    How is this possible? There were some clouds, so i suppose a bit of cloud effect could be possible, but i also measured when there was a clear patch and it measured around 5.7A for each panel, around 34A in total.

    Are we in a period of unprecented solar activity?
    You should be multiplying Isc (not Imp) by 1.56 for excess insolation and continuous use for your fuse size.
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    Re: Panels giving 140% of Imp ? help!

    C40 does not operate at Imp. Only MPPT controllers will operate in this range. Depending on panel type, with a PWM controller it will be operating closer to Isc. However, I would not expect more then 5% higher current then Imp.

    First guy complaining they are getting too much output. I have heard of reflection from a lake or a very white reflective roof stoking up output at a particular time of day.
  • Sulfur
    Sulfur Solar Expert Posts: 62 ✭✭
    Re: Panels giving 140% of Imp ? help!

    I had never heard of edge of cloud effect before today but I did see its effect on my system on March 9, 2013. I have been wondering what caused it and realized what was happening after reading a reply to your post. On March 9th, about the most my system could produce was 5300 watts in bright sun, but the edge of cloud effect made it produce 7100 watts briefly, that is a 34% increase in power. Were there clouds coming and going when you blew the fuse and when you measured the unusually high amps?
  • jaggedben
    jaggedben Solar Expert Posts: 230 ✭✭
    Re: Panels giving 140% of Imp ? help!
    ggunn wrote: »
    You should be multiplying Isc (not Imp) by 1.56 for excess insolation and continuous use for your fuse size.

    ...and for wire size.

    Don't know about Spain but in the US this is what the code requires, and you have seen the reason why.
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Panels giving 140% of Imp ? help!
    jaggedben wrote: »
    ...and for wire size.

    Don't know about Spain but in the US this is what the code requires, and you have seen the reason why.
    To pick a nit...

    You should first multiply Isc by 1.56 and see what conductor that calls for, and then multiply ISC by 1.25, introduce conditions of use deratings, and see what conductor that calls for, and then use the larger of the two (per John Wiles).
  • lazza
    lazza Solar Expert Posts: 336 ✭✭✭
    Re: Panels giving 140% of Imp ? help!

    HI Sulfur

    Not sure if they were coming and going, there did seem to be a lot of high cirrus clouds too and its rained alot lately, which I suppose gives good conditions for prismatic effects. The only other explanation is that the large PV field next door (huerto solar in spanish) may create a high albedo effect. Anyhow i'll be replacing the system 40A fuse for a 50A fuse in the next couple of weeks and i'll measure everything again... will let you know if there are any interesting findings!
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Panels giving 140% of Imp ? help!
    lazza wrote: »
    The only other explanation is that the large PV field next door (huerto solar in spanish) may create a high albedo effect.
    As in reflecting light onto your panels???

    You should be able to determine this by looking over at them and seeing how bright they look in terms of reflected light. Unless they are badly aimed trackers or amorphous silicon the effect should be short lived as the sun moves. I would not expect them to throw a shadow, of course, since they would be a distributed source.
    With a small test panel, just monitoring the Isc and using it as a light meter, you should be able to block off the direct sunlight and see what is left. Or put a "tunnel" around the test panel to eliminate all but the direct solar contribution.
    SMA SB 3000, old BP panels.
  • CALLD
    CALLD Solar Expert Posts: 230 ✭✭
    lazza wrote: »
    A Mystery:


    Are we in a period of unprecented solar activity?

    No not at all - seeing big power spikes is typical on cloudy days - I regularly see surges upward of 130% of rated power and sometimes even as high as 150% for brief periods. Paradoxically you can get higher production figures if there is just the right amount of cloud in the sky. The sunlight that your panels turn into electricity makes it's 93,000,000 mile journey from the stellar surface to your PV cells in 3 main ways: 1) Directly, 2)Absorbed by the atmosphere and re-emitted as diffuse light from the surrounding blue sky. 3) Reflection off surrounding objects.

    On a partly cloudy day the amount of light reflected from scattered clouds in the sky can be huge - as much as 30% of the total power received!

    It's very common for me to see anywhere between 1600 to 1900watts on my 1490w rated system on a partly cloudy day in summer as compared to 1350watts on a clear blue sky day.
    It's also quite common for me to see similar or even higher total daily production figures on a partly cloudy day.

    A blue sky is pretty dark if you block out the sun with your hand, but a sky full of scattered white clouds is very bright so even blocking out the sun still leaves a lot of bright light around...

    Sorry for dragging up this old thread, but I feel this subject doesn't get enough mention in the forums despite it's widespread occurrence.
  • raindog
    raindog Registered Users Posts: 32 ✭✭
    @CALLD : I agree, as a beginner, dealing with a small system in the Bahamas, where this phenomenon seems to be occurring almost every day and sometimes many times a day, all information concerning this EOC effect and how to resolve it is very helpful!  Thank you!
  • t00ls
    t00ls Solar Expert Posts: 245 ✭✭✭
    BB. said:
    Re: Panels giving 140% of Imp ? help!

    For maximum continous current rating of wiring/fuses/breakers, then you should multiply by 1.25x... So 32 amp Imp:

    32 amps * 1.25 NEC factor = 40 amp fuse+breaker rating minimum

    However, for pwm controllers which do not have any method of current control (unlike MPPT controllers which can limit their output to a specified level forever, safely and reliably), your should have another 1.25 safety factor:

    32 amps * 1.25 NEC solar factor * 1.25 NEC wiring factor = 50 amps

    So, if I understand NEC requirements correctly (no guarantee here), then you should be looking at 50 amp wiring/fusing.

    Note, for PWM controllers, cold weather does not materially affect Imp (Imp does drop a very tiny amount with falling temperatures), so this would be purely an edge of cloud/refections from snow, high altitude, water sand sort of event.

    -Bill
    ditto....I wasnt gonna go in depth.....but all of this ^^^^^^^^^^^^^^^^^^

    50 amp for the PWM controller .....42 amp for an MPPT ( I like a 2 amp safety cushion)
  • mike_s
    mike_s Registered Users Posts: 155 ✭✭
    Welcome to 5 years ago!