Over paneling

The manual for my cc reads 1.5 x over panel is ok.What are the advantages vs just using a bigger controller?
Blue ridge mts. Renogy 400 watts manual tracking . Epever mppt 30. 2 GC 208 ahr. 300 watt psw inverter. 2 kw genny. Iota 55.

Comments

  • littleharbor2littleharbor2 Posts: 947Solar Expert ✭✭✭✭
    edited June 29 #2
    Less than optimum conditions can still give full charging. On a RV, unless you can tilt your panels they will never be correctly oriented. Hazy conditions, hot panels ( especially flat on a RV roof) will have lower voltage, shading, etc.

    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, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

  • mcgivormcgivor Posts: 1,878Solar Expert ✭✭✭✭
    Over paneling with a limited controller will be advantageous only in limited sun, whereas the same amount of PV with a larger capacity controller will give more in all conditions, not to mention it's generally not good to run components at their limit for extended periods.
      1500W, 6× Schutten 250W Poly panels , Schneider 150 60 CC, Schneider SW 2524 inverter, 8×T105 GC 24V nominal 

  • BB.BB. Posts: 27,551Super Moderators admin
    Basically, saving money on having a smaller charge controller (vs 2x controllers--for example).

    Unless you are in a very cold climate, solar panels will generally output only 0.75 to 0.77 of rated power. It is common to "over panel" by 1/0.77 (~1.3x) or so. The charge controller will rarely "clip" output current.. And on cool/clear days, it may clip current by a relatively small amount for a short time on these "perfect" days.

    MPPT charge controller can naturally "throttle" output current to keep them within rated output conditions. And most should have thermal management too (if they get too warm, they will throttle back current too).

    It is a very good idea to keep electronics in a well ventilated area (not in a closet, under shelves, etc.)--High temperatures and large thermal cycling ranges (from very cold to very hot components) all serve to lower the actual lifetime of electronics.

    If you choose to "over panel" your MPPT charge controller, it is your choice... A question of $$$, space, and life/reliability of the system. It is very common to "over panel" good quality MPPT based charge controllers (and Grid Tied AC Inverters too).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mountainmanmountainman Posts: 109Registered Users ✭✭
    @Bb your math skills are amazing.  With 400 watts with a 30 amp mppt cc what are the chances of it ever producing 30 amps.
    Blue ridge mts. Renogy 400 watts manual tracking . Epever mppt 30. 2 GC 208 ahr. 300 watt psw inverter. 2 kw genny. Iota 55.
  • jonrjonr Posts: 991Solar Expert ✭✭✭✭
    Also note that on "perfect" days, you probably have more energy than you can make use of anyway - so no loss if it is throttled by the controller.

    I wouldn't worry about a good name brand controller running at its amp limit.
  • BB.BB. Posts: 27,551Super Moderators admin
    edited June 29 #7
    400 Watts x 0.77 derate x 1/14.5 volts battery = 21.24 amps on a very good non winter day peak charging current

    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mountainmanmountainman Posts: 109Registered Users ✭✭
    And  at -18c on a clear good day? 
    Blue ridge mts. Renogy 400 watts manual tracking . Epever mppt 30. 2 GC 208 ahr. 300 watt psw inverter. 2 kw genny. Iota 55.
  • BB.BB. Posts: 27,551Super Moderators admin
    400w x 1.0 deratex1 x /14.5 volts = 27.6 amps estimated

    Note that battery charging voltage matters too. If you have a will discharged battery bank, you could be at 13.5 volts or so....

    But during winter, if your battery back is -20C, the charging voltage will rise too.

    6 cells x (20C - - 20C) x 0.005 volts/cell/C = +1.2 volts increase over 20C room temperature charging voltage.

    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Posts: 7,701Solar Expert ✭✭✭✭
    The heat is on here in NorCalif  arrays output is way down, 1.9Kw from my 3kw array, even less on my 2kw array.   But the days are long and I still hit float.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • westbranchwestbranch Posts: 5,040Solar Expert ✭✭✭✭
    edited June 29 #11
    A few years back there were some smaller BlueSky Mppt CC's  that had a Watts limit and an Amperage limit.
    I gout one and was buying Mitsubishi  $800+ panels as I had the money...  the panels were rated at 7.8A and buried in the middle of the operators manual  there was a a22 Amp input limit, so I could only use 2 panels while I wanted to use 4....
    Here is the new useage headline  that differentiates between 36 and 60 cell PV's    since both are are now readily available...
    SB3000i. MPPT charge controller 12V/30A 400W for 36-cell panels or 12V/22A 290W for 60-cell panels.
    You really have to read all the little points! especially if you might overpanel...
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge, Hughes1100 Sat Modem
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • jonrjonr Posts: 991Solar Expert ✭✭✭✭
    On that bright -18C day, just as you start bulk charging (when voltage is low) of batteries located inside, I could foresee:

    400w x  1.1 derate / 13 volts = 33.8A.

    From a circuit design standpoint, it's not clear to me what the issue is with a DC-DC converter not allowing unlimited input amps.  Current flow into a buck converter is normally limited by inductor inductance and switch on-time.     Possibly they just mean that more than 1.5x over-paneling is wasteful.
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