"AM 1.5"

CALLD
CALLD Solar Expert Posts: 230 ✭✭
in Off Grid Solar & Battery Systems #1
I'm sure we have all seen this on the nameplate or spec sheet of their panels. It means sun at 48.2° from horizon at normal clear atmospheric conditions. It means one of my 300w panels should produce 300watts when facing the sun directly in these conditions...

More applicable to me though is the short circuit current on the nameplate - also applicable to "AM 1.5". It is 8.7 Amps per panel. Now I have 3 parallel strings in my setup. 8.7*3=26.1.

However I am now regularly seeing a stable output of 28Amps during clear spells close to midday. More interestingly the latest "edge of cloud surge" that tripped my charge controller's hit 35.2Amps!

Ok, so the sun was at an altitude of 67.2° from horizon at that moment, but for my PV to produce 135% surge surprised me! The concern of course is my charge controller, it now seems severely undersized, being only rated to 30Amps.

The other thing that dawned on me as well is being in the Southern Hemisphere, we quite literally have a "bigger sun" here in summer! Perihelion (Earth's closest point to Sun in it's orbit) occurs on 3 January, increasing solar radiation on Earth by 6.9% as compared to 4 July. 6.9% of 26.1 Amps is 1.8Amps. May not seem that significant but it all adds up.

The facts all point to me needing a better charge controller, especially seeing as most of the sun I am getting nowadays is in partly cloudy weather, which means those 35+Amps surges are going to be happening quite a lot...
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Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Re: "AM 1.5"

    It is one reason that a good quality MPPT (Maximum power point tracking) charge controller is nice choice compared with a PWM (Pulse width modulated) charge controller.

    An MPPT charge control can control its output current to it maximum rating, safely and efficiently.

    A PWM controller cannot--It's only choice is to shut down if overheating or over current from the array.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
    Re: "AM 1.5"

    Did it ever occur to you that the specifications on panels apply to laboratory test conditions and not the real world?

    There's all sorts of things that affect panel output: insolation, temperature, elevation, et cetera.

    The nameplate ratings, including Vmp and Imp, are relative guidelines that allow you to compare different panels and estimate approximate output under typical conditions. Change those conditions and you change the output.
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #4
    Re: "AM 1.5"
    CALLD wrote: »
    However I am now regularly seeing a stable output of 28Amps during clear spells close to midday. More interestingly the latest "edge of cloud surge" that tripped my charge controller's hit 35.2Amps!

    I take it this is a PWM charge Controller?

    You might try putting a fan on the charge controller, I've heard of Xantrex C60 (or maybe the Morningstar 60 amp?) going well over the rated amperage. with a bit of additional cooling.
    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.
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  • CALLD
    CALLD Solar Expert Posts: 230 ✭✭
    #5
    Re: "AM 1.5"
    Photowhit wrote: »
    I take it this is a PWM charge Controller?

    You might try putting a fan on the charge controller, I've heard of Xantrex C60 (or maybe the Morningstar 60 amp?) going well over the rated amperage. with a bit of additional cooling.

    Yes it's a PWM controller. Cooling doesn't seem to be the problem, I've never felt it even warm much to touch before even when running near full rated capacity for 3 hours.

    It does have the following over-current protection parameters:
    1.05-1.15C - shut down after 60 seconds, restart after 60 seconds.
    1.15-1.25C - shut down after 10 seconds, restart after 60 seconds.
    1.25-1.50C - shut down after 1 second, restart after 60 seconds.
    1.50C+ - shut down immediately, restart after 60 seconds.
    Restart attempts unlimited.

    I have a 40 amp breaker installed on PV lines, would be an issue if it tripped while I was away and relying on the intermittent sun to charge the batteries...
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #6
    Re: "AM 1.5"

    Get a second controller and split the array in 1/2 between the two controllers? Seems like you are very happy with your present PWM controller.

    Paralleling both controllers to a single battery bank (wire each controller directly to the bank, do not "daisy chain" from bank to controller A then to controller B--The resistance and current flowing through the common wires to the controllers could cause them to confuse themselves a bit (probably not charge as fast/stop charging a bit too soon because of the common wiring carrying current for both controllers and voltage drop from common wiring).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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