question on inverter/charging setup

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  • BB.BB. Super Moderators, Administrators Posts: 29,697 admin
    Re: question on inverter/charging setup

    In general, if Vmp matches within ~+10% (high to low) or better--Then you are OK for parallel connections.

    For Imp, again, ~+10% (high to low) or better for series connections.

    Note that each parallel string should have its own series protection fuse (or circuit breaker). If a string is shorted, then two or more parallel connected strings can send too much current to the shorted string and start a fire.

    For PWM parallel connections--As long as Vmp is above your minimum you want to use for the battery bank--Then "high Vmp" does not really matter--The paralleled string current is all that will add to the current through the controller (any "high Vmp" voltage is "wasted" with a PWM controller).

    Remember power = Volts*Amps ... For PWM controllers the Varray is controlled by the battery voltage and any controller/wiring voltage drops. Higher than needed Vmp/Voc will not do anything else (as long as you are under the maximum Vpanel rating of the PWM controller--and remember Voc/Vmp rise as air temperature falls).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Blackcherry04Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: question on inverter/charging setup

    I think it's only fair to point out to you that MPPT only operates in the Bulk mode, it is PWM in the Absorb and Float. So it depends on how much you pull from your batteries daily and the length of the Sun Hours if it is a Value to you. If you only go to 75% SOC or so, you probably do not gain much. Some buy them because of the features and some because they don't know their system well enough to know if it helps or not. For the cost difference between the two, I don't see how you can buy one and come out, Extra Panels are a no brainier.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: question on inverter/charging setup
    .... For the cost difference between the two, I don't see how you can buy one and come out, Extra Panels are a no brainier.

    Well, for one thing, the cost per watt of high voltage panels is generally a lot lower than the cost per watt of battery voltage panels.
    6 nominal 12 volt panels (~18 Vmp) at 180 watts each (1080 watts nominal, but each giving you only 10A Imp) would give you 60 amps total to the batteries. They will cost quite a bit more than 4 high voltage 250 watt panels (also 1000 watts nominal) which would give you just over 60 Amps. The difference in adjusted panel cost could make the added cost of the MPPT CC worth it.

    If you have plenty of space for panels, you would have to compare the current prices of both types of panels (in terms of cost amp delivered to the batteries) to make your decision.
    It is definitely not a mindless choice for MPPT if you can get a really good deal on LV panels, or if you already have some.
    SMA SB 3000, old BP panels.
  • NilaNila Solar Expert Posts: 173 ✭✭
    Re: question on inverter/charging setup

    Hi Everyone.

    Im going to start setting up tomorrow,

    Im going with 4 strings of 2 panels in series.. and I have got all the Mc4 connector plugs/ wires ,etc

    I have a combiner which has Fuses inside for all the positive lines , so I don't need to fuse them separately I believe.

    I am also moving my existing inverter/battery setup to the top floor of the house so it stays close to panels. :)

    Now , I might hire an electrician to do most of these but for wiring panels I might need to do that myself.

    Is there any safety precautions that I have to take for working with the 48v parts? like Panels/Charge controller,etc.

    I will keep all posted with any advances I make, Any advice is welcome.
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