Panel & charge controller sizing question?

PNW_Steve
PNW_Steve Registered Users Posts: 79 ✭✭
Hello Everyone,

I am working on solar installs for a couple of RV's and have been looking about for good values on the parts & pieces.

This morning I found an outfit (Santan Solar) on Ebay that has 315watt panels for around $100 each. That got me wondering about the possibility of adding additional panels in order to improve output in lower light situations.

My question revolves around panel capacity / controller sizing.

If I oversize the panels is there reasonable protection in the name brand controllers to keep me from letting the magic smoke out? Can I place 1800 watts of panels on a 60 amp controller with a 24v battery bank and "program" the controller to limit current to within the spec's of the controller?

My thought is that panels are relatively cheap and if I can significantly improve output in reduced light conditions that it may be worth throwing another $200-$300 in panels into the mix.

In a perfect world I would install more panels, a larger charge controller and a bigger battery bank. The deal killer is the batteries. Space, weight and cost are the "perfect storm" that is limiting battery bank size to 24v-230A/H.

What do you all think?

Thanks.

S.

Comments

  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,044 ✭✭✭✭✭
    Keep in mind these panels are  about 3' 3" x 6' 6" They are huge and finding a shadow free area that large on an RV roof can be tough. Add to that freight is going to add considerably to their cost and they are incomplete modules. You will need to finish building them and, hopefully end up with a finished product that lasts in the elements.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    Current from the panels will depend on the charge controller load.  The controller will self-protect against drawing too much current (but not necessarily too much voltage).  When the batteries are almost full, for example, the controller will draw a smaller current even if the panels could produce much more.  Voltage is determined by panel wiring and environmental conditions.

    You will need to consider whether adding the new panel (in parallel?) will be consistent with the existing panels and wire size.
    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
  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    Many / most higher end MPPT type controllers will can be asked to limit output current. Set that to the proper high end of your battery bank 13-15% for flooded lead acid, higher for some AGM I'm always curious if this will shorten their lives, perhaps Marc can let us know.
    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.
  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    Photowhit - I don't limit cc output with theoretical panel capacity of well over 15% of FLA capacity. The batteries won't accept it even if it's there.
    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
  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    Might check that, It might be that they dissipate the extra as heat...

    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.
  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    PNW_Steve said:
    Hello Everyone,

    I am working on solar installs for a couple of RV's and have been looking about for good values on the parts & pieces.

    This morning I found an outfit (Santan Solar) on Ebay that has 315watt panels for around $100 each. That got me wondering about the possibility of adding additional panels in order to improve output in lower light situations.

    My question revolves around panel capacity / controller sizing.

    If I oversize the panels is there reasonable protection in the name brand controllers to keep me from letting the magic smoke out? Can I place 1800 watts of panels on a 60 amp controller with a 24v battery bank and "program" the controller to limit current to within the spec's of the controller?

    My thought is that panels are relatively cheap and if I can significantly improve output in reduced light conditions that it may be worth throwing another $200-$300 in panels into the mix.

    In a perfect world I would install more panels, a larger charge controller and a bigger battery bank. The deal killer is the batteries. Space, weight and cost are the "perfect storm" that is limiting battery bank size to 24v-230A/H.

    What do you all think?

    Thanks.

    S.


    Hi PNW_Steve,

    Cannot speak to those exact PVs,

    But,  1800 W of PVs on a 24 V system will,  generally not need any current limiting on  a CC,  as,  the expected output from this amount of PVs on a 24 V system is below the maximum output spec of a 60 A CC.

    For normal conditions,   a 1800 W PV array would not produce much more than about 75% of the STC output of the array.   This would be about 56 - 60 Amps maximum from the PV array.

    FWIW,   Vic

    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.