SW-4024, XW60-150, 3000W Panel, 24V@400AH Battery Bank

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onthesolar
onthesolar Registered Users Posts: 21 ✭✭
in Solar Beginners Corner #1
The system is located in India, power cuts are often and utility rates are high. I understand solar is not essentially cheap but I started off with this as an experiment to see if I can use this as a power backup and at the same time to bring down my utility usage. So when the sun is available, I want to run only on Solar and not on utility. I plan to install a solar priority controller to accomplish this. Below is a description of my setup and then let me ask my question.

I have 12 250W mono panels divided into 4 strings. Each string produces an open circuit voltage of 120V and current of 7A. The strings are all connected in parallel and connected to both charge controllers in parallel as well. The charge controller outputs are in parallel connected to the battery. The SW4024 is connected to the battery and utility power.

My question is about wiring between the array and the charge controller. Initially a single charge controller was installed, however my installer described to me the SW4024 and the battery bank are 24 volts system and each charge controller can support only 60 Amps, so the maximum power that can be derived from a single CC is only 1440 watts. So his rationale was to add another charge controller to the array in parallel which will add another 1440 watts thus making total output power available form the CC to be 2880 watts. He believes thus the system can make use of the entire 3000 watts that can be potentially harvested from the panel.

However based on my understanding of how a MPPT charge controller works, I felt this wiring configuration might be incorrect and I am suggesting the installer that the array needs to be split into 2. Each array should contain 2 strings in parallel providing 120 volts and 14 amps. Each of these have to be independently connected to their own charge controller. Only the outputs of the charge controller should be connected in parallel to the battery.

I would like understand which is the correct wiring pattern and why?

Thanks for the help
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #2
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    Re: SW-4024, XW60-150, 3000W Panel, 24V@400AH Battery Bank
    onthesolar wrote: »
    However based on my understanding of how a MPPT charge controller works, I felt this wiring configuration might be incorrect and I am suggesting the installer that the array needs to be split into 2. Each array should contain 2 strings in parallel providing 120 volts and 14 amps. Each of these have to be independently connected to their own charge controller. Only the outputs of the charge controller should be connected in parallel to the battery.

    Yes, 6 panels on each controller in the configuration you suggest: 2 parallel strings of 3. This really should have been a 48v system from the start and you could have saved yourself a controller.
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  • onthesolar
    onthesolar Registered Users Posts: 21 ✭✭
    #3
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    Re: SW-4024, XW60-150, 3000W Panel, 24V@400AH Battery Bank

    Thanks stephendv. I will be getting this done in the next day or two, I will keep the forum updated. I am hoping this change will increase the power output from the CC, right now they maximum they are giving out is close to 1200 watts. I will report once complete.
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  • onthesolar
    onthesolar Registered Users Posts: 21 ✭✭
    #4
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    Re: SW-4024, XW60-150, 3000W Panel, 24V@400AH Battery Bank

    Late last week, I had the changes done with strings separated and going to individual charge controllers. I have a Phocos solar priority controller that switches to PV power charge mode in the morning as the sun rises and shuts down PV as darkness sets in. It as well switches to Grid power if the battery goes below 24.4 V. During the day the battery generally at ~26 V. When there is not sufficient PV power (dawn and dusk), the load is on the battery, will this cycle reduce the life of the battery?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #5
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    Re: SW-4024, XW60-150, 3000W Panel, 24V@400AH Battery Bank

    It sounds like you are not recharging the (flooded cell lead acid?) batteries very well... If you are discharging them at night and charging them during the day time with solar--You should be holding the battery voltage near 29 volts. Bulk from ~26-29 volts (as battery charges with full current available from the solar array) and hold at ~2-4+ hours at ~29 volts (absorb).

    If the batteries sit at 26 volts during the day (when they should be charging)--You are not putting enough current into the battery bank.

    This could because of miss-programmed Solar Charge controller and/or SW inverter.

    Are you running the SW inverter as a "Grid Tied" inverter during the day time (pumping energy into the grid)?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • onthesolar
    onthesolar Registered Users Posts: 21 ✭✭
    #6
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    Re: SW-4024, XW60-150, 3000W Panel, 24V@400AH Battery Bank

    It is not Grid Tied (there is no net metering). I have seen the battery up to 27.6V during the day.

    It is not discharging through the night, battery discharges between 6 and 8 PM. The battery reaches below 24.4 volts about 8 PM and the switch transfers the load/charging to the grid. Once there is enough sunlight about 7 am next day, the switch transfers completely to solar.
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