Label underated?

SolaRAC
SolaRAC Solar Expert Posts: 52 ✭✭✭✭
in Solar Beginners Corner #1
So my 75 watt panel's label says its rated at Imp of 4.41a and Ics of 4.72a. There is a "Tolerence" of +/-5%. Thing is, I've been seeing 5.5amps pulled for almost an hour now according to my charge controller.

Should I be concerned?

What kind of performance are your guys getting compared to your rating?
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Comments

  • SolaRevolution
    SolaRevolution Solar Expert Posts: 410 ✭✭
    #2
    Re: Label underated?

    Is your controller an MPPT?
    Is it cold?

    The PV panel's maximum power voltage is higher than the battery voltage. A MPPT CC converts this "extra" voltage into additional current. A cold panel can put out higher than rated voltage and the effect of the MPPT current boost can be even greater.

    If it is not an MPPT you have a mystery.

    Alex
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  • SolaRAC
    SolaRAC Solar Expert Posts: 52 ✭✭✭✭
    #3
    Re: Label underated?

    Sunforce 30 amp Digital PWM Controller
    84F outside today...

    Again, should i be concerned?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #4
    Re: Label underated?

    If the panels are "thin film" type--The will generate ~25% more rated power for the first few months as they "burn in" down to there rated values (crystalline panels may generate.

    If you are running 30 Vmp panels on a 12 volt PWM battery bank, you will get higher than Imp.

    Also, Imp does rise, very slightly with increasing temperature... Where as Vmp drops significantly with higher temps.

    So, with a PWM controller--You will not see Imp drop unless Vmp-array-hot fall so much, that it can no longer supply enough voltage to the battery bank to drive rated current.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • mejustme
    mejustme Registered Users Posts: 17 ✭
    #5
    Re: Label underated?

    Hi

    Are there any large reflective surfaces that could increase the light aimed at the panel?

    I have a large sloped roof next door that seems to allow a small panel to work when it probably should not.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: Label underated?

    Let's see, a 75 Watt panel with Imp of 4.41 would be Vmp 17.0

    The thing I'd be concerned about is the controller's meter being off by 25%.
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  • SolaRAC
    SolaRAC Solar Expert Posts: 52 ✭✭✭✭
    #7
    Re: Label underated?

    With regard to reflective surfaces, the panel has been fixed in one spot for two... Maybe three weeks; this is the first time I got 5amps from it. In fact... It peaked at 6amps a few times today for maybe 3-5 seconds at a time.

    As Cariboocoot said, maybe my CC is reading incorrectly. I will test this tomorow if i get the same readings using my amp meter.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #8
    Re: Label underated?

    reflections can start to appear later as they would vary with time of year. the further spikes you are seeing could even be edge of cloud, but i would suspect the meter to be reading a tad high too.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #9
    Re: Label underated?

    It is not unusual for some charge controller units to read 5% to 10% high... Probably very few read low (:roll:).

    To read "exact" (within 2% or so), a relatively precision current shunt needs to be employed. For normal functionality (such as MPPT), accurate measurements are not necessary--Just repeatable over short periods of time (such as during a MPPT scan looking for Vmp*Imp=Pmp while varying current) to find the optimum power point. Those measurements can be estimated from other components in the meter that are not ideal for calibrated current readings (saves cost).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • SolaRAC
    SolaRAC Solar Expert Posts: 52 ✭✭✭✭
    #10
    Re: Label underated?

    So the CC is spiking at a whopping 5.9amps today..

    I put my amp meter in line and sure enough it was relatively the same reading ~5.7 amps. Keep in mind my panel is rated for 4.4amps.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #11
    Re: Label underated?

    are you sure of the model you have or maybe it was marked wrongly, even though unlikely? if it is true then don't look a gift horse in the mouth.
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  • SolaRAC
    SolaRAC Solar Expert Posts: 52 ✭✭✭✭
    #12
    Re: Label underated?

    And this is my first panel :)

    I guess I am lucky. I will continue to monitor it and let you guys know how it goes after about a month.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #13
    Re: Label underated?

    try a short circuit test if your meter is capable of it and see what it goes to. remember it's high current and will arc if you put the meter leads to or from the leads so maybe switch it in and out somehow.
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