pv to inverter voltage

robocoprobocop Registered Users Posts: 77 ✭✭
Hi
i have just change my inverter to an 8kw hybrid from mpp company.
have 8 solar  panels of 500w each
voc 58.95  isc 10.28  
had in parrallel and serie  total 98v  and the company said the best is 8 panel in serie gives me 472

max voc of 500vdc  the inverter take 

had a question as both the 98v and the 472b v charge the batteries but which combination is better?

have 16 batt of 12 v 250 ah

awaiting a reply  of some of my friens on this forum

Bob

Comments

  • BB.BB. Super Moderators, Administrators Posts: 31,684 admin
    Bob,

    Can you give us a link to the Hybrid Inverter specifications you wish to use?

    Also, what are the Vmp/Imp specifications of your panels?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.BB. Super Moderators, Administrators Posts: 31,684 admin
    hi Bill

    model pip8048max    max pv array power 8kw  max pv array open circuit voltage   500vdc   pv  array   mppt range  90vdc-450vdc

    start up voltage voc   80vdc

    panel vmp 48.63   voc  58.95   imp 10.87A   isc 10.28 A

    its written : please make sure that the max input voltage of each pv input connector is 18smile

    for your info  I do have 4 battery banks in use  each battery is250ah 12v 

    Hope this is sufficient

    Robert
    sorry i mean  max input current of each pv input connecter is 18A
    Good day Robert,

    First, we should keep the discussions in your "thread", and not post on your wall (don't check walls for Q&A's).

    I did not find a manual on a quick search--Just these links:
    https://www.mppsolar.com/v3/pip-max/
    http://www.mppsolar.com/v3/catalogs/PIP-MAX.pdf

    This unit has 2x solar input PV inputs, each a max of 18 Amps.

    With your panels having an Imp of 10.87 Amps it looks like you are limited to one string per input. 100 VDC minimum (Vmp-array-hot) and 500 VDC max (Voc-array-cold).

    You are on a warm Caribbean island Curaçao as I recall, so you do not have very cold winter temperatures (not below 20C?).

    The min/max number of series connected panels:
    • 100 VDC / 48.63 Vmp-std = 2 panel in series minimum ( would suggest 3 series to allow for hot panels/hot weather relaible starting of charge controller)
    • 500 VDC / 58.95 Voc-cold = 8.45 = 8 panels max series
    • 8 series panels * 48.63 volts Vmp * 10.87 amps Imp per string (one per 2 total PV inputs) = 4,229 Watt array with 8 panels only
    • 8 series panels * 48.63 volts Vmp * 10.87 amps Imp * 2 parallel strings (one per 2 total PV inputs) = 8,458 Watt maximum array with 16 panels
    • 4,229 Watt array * 0.77 typical panel+controller deratings = 3,256 Watts typical best case (cool/clear day/solar noon/ few hours a year)
    • 3,256 Watt effective array * 1/59 volts battery charging = 55 Amps typical "best case" charging current with 8 panels (at 59 VDC battery bus--Max of controller 120 Amps)
    • You have the option of 8 series x 1 string, or, 4 series x 2 strings... Either would work (suggest 8s x 1p as you can use smaller diameter copper wire and/or longer wire run from array to inverter-charger)
    If you have 4 batteries total (12 volt @ 250 AH)... Are these flooded cell Lead Acid batteries or something else? Assuming Lead Acid (and as a general starting point), the maximum suggested AC inverter and array for a 48 volt @ 250 AH battery bank:
    • 1,000 Watt AC inverter and solar array suggested max per 100 AH battery bank * 250 AH = 2,500 Watt max AC inverter and array
    So--If 4x batteries in series for a 48v @ 250 AH bank, this is really too small for a 4,000 Watt array (ideally a minimum of 400 AH battery bank) and for an 8kW inverter should be ~800 AH @ 48 volt battery bank.

    For a solar array, fixed:
    http://www.solarelectricityhandbook.com/solar-irradiance.html

    Willemstad
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 78° angle from vertical:
    (For best year-round performance)

    JanFebMarAprMayJun
    6.65
     
    6.95
     
    6.92
     
    6.23
     
    6.58
     
    6.78
     
    JulAugSepOctNovDec
    6.74
     
    6.61
     
    6.42
     
    6.41
     
    6.28
     
    6.32
     

    The average daily harvest for April on a fixed array woud be:
    • 4,229 Watt array * 0.52 off grid AC system eff * 6.23 hours of sun per day (April) = 13,700 WH per day
    The average Tare Load from AC inverter (on but no loads) is ~70 Watts:
    • 70 watts * 24 hours per day = 1,680 WH per day (or >10%  of your daily harvest)
    • 70 Watts / 48 VDC battery bank = 1.5 amps
    • 1.5 amps inverter Tare * 24 hours per day = 36 AH
    • 36 AH per day / 250 AH battery bank = 0.144 = 14.4% of your battery bank capacity discharge
    At this point, I worry that your system is not well "balanced"... A very small battery bank for the solar array. And a way oversized AC inverter for the small battery bank.

    If there are special needs (lots of power for a short period of time--Such as a shop) and used AGM or LiFePO4 batteries--Maybe would make sense for your needs. On the other hand, you do live in a "very sunny" location.

    Also one quick search for your hybrid inverter-solar charger--Make sure you have current firmware--They have been making updates/bug fixes:

    https://forums.aeva.asn.au/viewtopic.php?t=6714

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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