Help with expectations

kelperis
kelperis Registered Users Posts: 45 ✭✭
in General Solar Power Topics #1

I finally got my first PV panel up. It is a 175W 12V 9A panel. It has 10awg wire going 10 feet to a combiner box. From there it has a 6awg wire running about 15feet to my charge controller. Unfortunately, it is a cloudy day, but I am only getting 2amps at the charge controller, even though I am getting about 5amps at panel itself. Should I expect this, or does anyone have a suggestion.

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  • kelperis
    kelperis Registered Users Posts: 45 ✭✭
    #2

    Did a little more digging, and one article indicated that on cloudy days, you can only expect 10-25% of full capacity. By my calculations, I am currently getting 15%, so I guess this could be within normal range for the weather today. I am still not sure about the drop from the panel to the cc. That should be consistent regardless of what the panels are producing. Thoughts?

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  • kelperis
    kelperis Registered Users Posts: 45 ✭✭
    #3

    Here are the measurements at each point along the way. I seem to be dropping 50% or more from the panel to the batteries. Keep in mind that these measurements did not occur at the exact same time, so some of it could be fluctuations.


    Measurements

    panel = 6amps

    combiner = 3.8amps

    cc = 3.3amps

    VictronConnect = 2.5amps

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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #4

    How are you measuring current?

    What load(s). If battery, what size and state of charge?

    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #5

    I think you are measuring open circuit, The farther away from the panel, the more 'load' you are presenting in the for of resistance in the wire. Unless you have distinct shades I wouldn't expect more than 10% of the panels potential.

    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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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #6

    Assuming no shadows on the panel, if you short the panel output (or just one cell), the short circuit current of a solar panel is within 10% of the solar energy of the panel. (100% Isc = 1,000 watts per square meter).

    You can use a low value power resistor (Isc×R = voltage drop, which should be 0.100 volts or so maximum).

    Or can just short the panel output and use a DC current clamp meter to measure Isc.

    You can use any crystalline cell panel or even a single cell. As long as the reference panel faces the sun at the same angle, it should be s good reference what your solar array can output (xx% × Imp).

    Remember, if your load (charge controller, etc.) only needs a fraction of the current or energy, it may (and will) draw led than 100% of the sun + array available power at that moment.

    Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • kelperis
    kelperis Registered Users Posts: 45 ✭✭
    #7
    https://forum.solar-electric.com/discussion/comment/397194#Comment_397194

    I am using a mastech clamp meter to measure the DC amps. I did not have any of the inverters turned on, but there is a .5amp draw. The batteries are 6 200ah in parallel for 1200Ah total. They are Renogy gel batteries. The state of charge was 95%

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  • kelperis
    kelperis Registered Users Posts: 45 ✭✭
    #8
    https://forum.solar-electric.com/discussion/comment/397195#Comment_397195

    It was overcast, the panels are maxed at 9amps, but only producing 6amps and the connector on the panel. I assumed it was from the overcast. So are you saying that 10 feet of 10awg wire will cause nearly a 45% drop in current?

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #9

    What voltage are you seeing on the battery bus?

    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • kelperis
    kelperis Registered Users Posts: 45 ✭✭
    #10
    https://forum.solar-electric.com/discussion/comment/397204#Comment_397204

    I will measure it again tomorrow and let you know

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  • Wheelman55
    Wheelman55 Registered Users Posts: 244 ✭✭✭
    #11

    kelperis. I am not an expert, but this seems normal.

    I’ve got a ZAMP 180 watt portable unit. It’s rated at 10 amps, which it will put out in full sun conditions IF pointed directly at the sun.

    On partly cloudy days I get less. When not pointed right at the sun I get less. On completely overcast days I get way less, like 0.5 amps or less.

    FYI, on a fully overcast day you get the best output by pointing the panels straight up (flat).

    Also the amps go down when you approach full charge.

    PS. That seems like a lot of battery for a 9 a single 175 watt panel. Once again, I am not an expert.

    Off-Grid in Terlingua, TX
    5,000 watt array - 14 CS 370 watt modules. HZLA horizontal tracker. Schneider: XW6048NA+, Mini PDP, MPPT 80-600, SCP. 390ah LiFeP04 battery bank - 3 Discover AES 42-48-6650 48 volt 130ah LiFePO4 batteries
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  • kelperis
    kelperis Registered Users Posts: 45 ✭✭
    #12
    https://forum.solar-electric.com/discussion/comment/397210#Comment_397210

    Thanks. I have 12 more panels to hook up. Just trying to get the kinks worked out before I turn up all the panels. I can probably trim some cables to minimize the lengths, maybe reduce it by a few feet. It’s exciting to get anything right now, even if is only enough to charge my phone. I can’t point all the panels straight up, but I do have four that are on a different rack that I count set up that way so that on overcast days I can get a few more amps.

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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #13

    NO! I'm saying you have NEVER measured a load! You are just sticking a meter to an open circuit.

    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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  • kelperis
    kelperis Registered Users Posts: 45 ✭✭
    #14
    https://forum.solar-electric.com/discussion/comment/397218#Comment_397218

    Ok, I see what you are saying. The load was about 3amps. I was under the impressions that batteries not 100 SOC, uses all available current. So yes, I was expecting to see it pull everything the panels could produce. Today, the sun still isn’t out, but it is brighter, and the CC is showing it getting 15amp from the panels, which is abou 80% of the max for the two panels. Thanks for your help, it seems to be working better today.

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