brownbearbrownbear Registered Users Posts: 30 ✭✭
Right now I have two 100w panels that give about 119w.    So I'm getting about half bc of losses.  If I wanted to get 1,000w of power does that mean I'll need 2,000 watts of panels?  For example, seven 300w panels to get 2,100w which will actually give me 1,050w.   I'm looking for an off grid set up.   


  • MrM1MrM1 Registered Users Posts: 478 ✭✭✭
    edited February 2019 #2
    I am a little confused about your 119 W.  Is that the highest number you see on any given day?  Full Sun?   Solar Noon?   Surely you don't mean Watt hours per day.
    I have 9 285W Solar panels and see on average about 1900 watts if the sun is out around peak times consistently.  I can produce up to 10.5 kWh per day in N FL with about 4.3 sun hours average per day.
    In the spring before the summer heat really heats up the panels I have see them occasionally hit just under 2300 Watts.  Not bad for a 2565 Watt array.  But I know panels lose some rated power over the years. 
    Off Grid?  You will need a lot more than 2 100 watt panels.    I would say my system is a bare minimum for what it would take comfortably.  I am sure others can do it for a bit less power per day, but not much less.  Especially running a well pump and full size fridge.  (no AC)
    REC TwinPeak 2 285W 3S-3P 2.6kW-STC / 1.9kW-NMOT Array / MN Solar Classic 150 / 2017 Conext SW 4024 Inverter latest firmware / OB PSX-240 Autotransfomer for load balancing / Trojan L16H-AC 435Ah bank 4S connected to Inverter with 7' of 4/0 cable / 24 volt system / Grid-Assist or Backup Solar Generator System Powering 3200Whs Daily / System went Online Oct 2017 / System, Pics and Discussion
  • BB.BB. Super Moderators, Administrators Posts: 30,944 admin
    As always, details matter... Temperature and aiming of panels at sun (Cosine error), atmospheric clarity/humidity/etc., temperature of cells, charge controller type and what charge mode it was in (bulk, absorb, etc.), battery bank state of charge/bus voltage, specifications of panels, etc.

    The typical best case noontime harvest (all things being taken into account towards "best harvest") is around 75% to 77% of "rated wattage" for panels. You won't hit this value every day--But is a good maximum that most people will see once in a while.

    If your using a PWM controller and the panels are Vmp~18 volts in parallel, and the battery bank is ~80% or less state of charge (and the charge controller is in "bulk"), you should see pretty close to Imp-array going into the battery bank.

    You could also wire the panels directly to the battery bank (bypass the PWM charge controller), that will give you the best harvest capable from the solar panels at that point in time...

    Seeing 50% of rated output from the array is a bit on the low side, but it is hard to say if something is bad or misprogrammed (like the charge controller) or you could have wiring issues (lose, dirty, corroded, to small of AWG, to long of wire run, etc.). 

    Using a voltmeter, you can check the voltage at the solar panels, Vpanel input of the charge controller, Vbatt output of charge controller, and Vbatt-bus connection. Between Vbatt-controller and Vbatt-bus, you should see a maximum of (ideally) 0.05 to 0.10 volt drop from controller to battery bank with near rated current flow. Too much voltage drop, and the controller may go into absorb charge (constant voltage like 14.75 volts) and reduce charging current early.

    Vpanel for a PWM controller should be near to Vbatt (maybe Vbatt +1-2 volts).

    And using a DC Current Clamp DMM, you can measure the current of each solar panel (if in parallel), to see if their output current is closely matching (mismatched current flow, could be a failing panel).

    If you do not have a current meter, you can connect only one solar panel at a time to see that they both have similar current output.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Solar Expert Posts: 8,965 ✭✭✭✭✭
    Generally, you can expect about 70% of nameplate, for well aimed panels in sunny exposure.  As aim declines, so does harvest.
    Clouds, haze, shadows all reduce harvest
    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

    gen: ,

  • mountainmanmountainman Registered Users Posts: 430 ✭✭
    In Myrtle beach sc 2 100 watt panels clear day yesterday on a very low battery 75°f at 11 am was 163 watts 12.4 amps 13.2 volts mppt.
    2kw array 6 345 q cells  make sky blue 60 cc
     6 230ah GC @36 volts 
    18 amp accusense charger. 3650 champion 
  • littleharbor2littleharbor2 Solar Expert Posts: 1,547 ✭✭✭✭
    Are the panels tilted to the correct angle or, possibly lying flat level? 

    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.

  • brownbearbrownbear Registered Users Posts: 30 ✭✭
    edited February 2019 #7

    I have 2 100w panels and this is the highest I've seen them go.  That's why I'm saying if I want 1,000w should I get 2,000w worth of panels.   
  • mountainmanmountainman Registered Users Posts: 430 ✭✭
    edited February 2019 #8
    Short answer no. Unless panels are mounted flat or you have shading issues. Or using pwm in extreme heat!!  IMHO  Expect 75~80% of rating. Are your panels in parrelell on mppt? If so try putting them in series.
    2kw array 6 345 q cells  make sky blue 60 cc
     6 230ah GC @36 volts 
    18 amp accusense charger. 3650 champion 
  • EstragonEstragon Registered Users Posts: 4,478 ✭✭✭✭✭
    +1 on putting them in series (assuming mppt controller... if pwm I think voltage would be near Vbatt?).  At 16.8v mppt may be having trouble getting a good max power point.
    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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