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Abdul
Abdul Registered Users, Users Awaiting Email Confirmation Posts: 1 ✭
in Solar Beginners Corner #1
Hello 
      I have four 175watt 36volt solar panels connect in series to a 40Ah 150 Max volt MPPT. to charge 12volt 2x 200ah battery can this work?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Yes, the system will be "functional"... It will support either 2x 200 AH batteries in parallel (for 12 volts @ 400 AH) or 2x 200 AH batteries in series (for 24 volts @ 200 AH)... The energy storage will be the same--Just depends on your DC power needs (12 VDC or 24 VDC battery bus--Assuming the MPPT controller is 12/24 VDC battery compatible--Which most of these MPPT types are).

    The solar array would work well with 2 panels in series * 2 strings in parallel (this configuration is needed for 24 VDC battery bus for optimum results). Will also work for 12 volt battery bus too (and allow you to install the solar array farther away from the charger/battery bank--using smaller diameter copper wires).

    Size wise, suggest a 10% rate of charge for your battery bank for full time off grid... A 12 volt * 400 AH battery bank (array sizing is the same for 24 volt * 200 AH) would be:
    • 4 * 175 Watt panels * 0.77 panel+controller deratings * 1/14.5 volt battery bus  = ~37 Amps typical best case max current (works with 40 Amp controller)
    The suggested array size would be:
    • 400 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 753 Watt array "nominal" suggested
    Which is certainly close enough to your 4*175W=700 Watt array for a nice setup.

    Next question is where are you located to calculate the amount of "useful energy" per day by season... Fixed array, tilted for 15 degrees from horizontal, for DAKAR, SENEGAL (nothing closer to Freetown Sierra Leone?). 

    https://pvwatts.nrel.gov/pvwatts.php

    Pretty sunny location, on average... Pick December @ 5.03 hours of sun per day for "worst case" calculation:
    • 4 * 175 Watt panels * 0.77 panel+controller deratings  * 5.03 hours of sun for average December = 2,711 WH per average December day
    Unless you have a backup genset--Suggest only using 50% to 65% of "predicted average power" from solar system (clouds, bad weather, etc.). For example:
    • 2,711 Watt*Hours per Ave Dec Day * 0.65 solar derating = 1,762 WH suggested daily Dec loads
    • 1,762 WH per day / 12 volts = 147 AH per day @ 12 volt average Dec Loads
    That is how the math works... Of course, if your loads vary by seasons/months, you have a backup Genset, or variable loads (such as water pumping), you can modify the math for better model your needs/location...

    Of course, there are other details (diameter/length of copper wiring, surge of loads, using an AC inverter, backup Genset, etc.)--But this is a good start to understand the solar side of the equations.

    Questions?

    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,102 ✭✭✭✭✭
    #3
    What is the Voc of those panels? If in the 45 volt range, you need to wire 2s2p. 4s wiring will give too high of a Voc for that MPPT controller.

    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,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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