Second panel needed

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garynappi
garynappi Registered Users Posts: 105 ✭✭
edited September 2019 in Solar Beginners Corner #1
I searched for relevant topics and did not find any discussion relating directly to my issue. 

I didn't think I'd post something like this living in sunny south Florida, but due to a recent string of cloudy days it came up. 

For the third day due to offshore storm influence, I've had cloud cover interspersed with full sun but my battery has not yet taken a full charge from my 100w panel by the third day. I'm a bit concerned that my outside lighting (95Ah "dual purpose" starting / deep cycle) will be LVD'd from a low battery by my controller and not take a full charge for several days thereafter. To add to the confusion my Morningstar CC "claims" it is charging when the solar panel voltage is just above 12.1 volts.

So, I planned the system (DC lighting only no inverter) with flexibility of a combiner thanks to advice from forum members and I'm figuring that I may need another 100 watt panel. 

If what I read is close to correct (80-90% drop in efficiency on cloudy days) given my light loads (no more than 30% of the battery reserve used after a full night of lighting and previous day full charge) a second 100w panel "should" keep my battery topped off at least most of the time? 

I'm terrible with the concepts of solar system issues of losses, battery charge math but I'm thinking my suppositions may put me in a better state?
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #2
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    Do you have an alternate charging source (eg a grid or generator powered AC battery charger)?

    If the battery gets down to < controller LBCO,  it may never charge unless/until charged by non-solar means.  Also, taking the battery down that far regularly can result in permanent damage.  LBCO is to protect the controller, not the battery.

    If the controller is a pwm type, it will pull panel voltage down to near battery voltage when charging.  This is normal for pwm.

    The drop in charging current on cloudy days depends on how thick the clouds are.  I've had cloudy days when enough light gets through to get batteries full.  Today is really gloomy so far though, and I'm getting zero charge current.

    With a draw of 30%, a second panel may not be a bad idea.  On lightly overcast days, that will help get more current from what light there is.  A non-solar means of charging should still be available though, as pretty much everywhere has long enough runs of gloomy weather at least occasionally for a backup means of charging to be needed.
    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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  • garynappi
    garynappi Registered Users Posts: 105 ✭✭
    #3
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    Thx Estragon,

    I do have an AC charger (I'm a motorcyclist and boater too, NP there) but I'd need to run extension cords across the patio deck. It's a possible, and even though infrequent it's a less elegant solution. 

    When my panel mount and interfaces were in the prototype / build phase (I'm kinda anal / slow to make decisions) I had to use a charger for a few months because the panel was oriented to the west, it was a relief to get it up and charging without A/C.

    You said, "If the controller is a pwm type, it will pull panel voltage down to near battery voltage when charging.  This is normal for pwm." 

    This I did not know, thx.

    Well it looks like a second panel may be my best solution. 






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  • garynappi
    garynappi Registered Users Posts: 105 ✭✭
    #4
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    I wound up adding a 125 watt panel in addition to the 100 watt installed and after three cloudy / rainy days and I've not yet gotten to the LVP level. 




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