solar mppt

lavanya
lavanya Registered Users Posts: 1 ✭
in Solar Beginners Corner #1
can someone help me out in solving this problem
A photovoltaic module has a open circuit voltage of 16V and short circuit current of 3A. This PV module is directly connected to a battery which has a no-load voltage of 12V. The battery is getting charged from the PV module. The most appropriate operating point is??
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,113 ✭✭✭✭✭
    #2
    If your panel has only a 16 Voc. output you will never be able to charge your 12 volt battery. The Vmp. will be lower than the Voc. and once the panel warms up in the sun the voltage will drop below any useful level to charge a 12 volt battery. 

    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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  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    edited September 2018 #3
    The most appropriate operating point depends on the state of the battery.  But assuming it is a typical lead acid battery, this will max out at about 14.4V.   At cooler temperatures, your panel can produce this, although at much less than 3A.  At warmer temperatures, you will only get a partial charge (very bad for a lead acid battery).

    Unless this is a float application, you should be using a panel more like 21V open circuit.

    I am available for custom hardware/firmware development

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  • bill von novak
    bill von novak Solar Expert Posts: 891 ✭✭✭✭
    #4
    lavanya said:
    can someone help me out in solving this problem
    A photovoltaic module has a open circuit voltage of 16V and short circuit current of 3A. This PV module is directly connected to a battery which has a no-load voltage of 12V. The battery is getting charged from the PV module. The most appropriate operating point is??
    Not sure of your question.

    The most efficient operating point of the panel will be around 12.8V at 25C - lower at higher temperatures. The battery needs to be charged at 13.8 to 14.5 volts, depending on type/phase of charging.  The actual operating point when you connect the two directly will be determined by the battery, and will be higher than ideal (so you won't get full current from the panel.)  I'd expect to see weak charging that will not entirely charge the battery as the panel warms up.  (At 50C Vmp will drop to 11.9 volts, and Voc will drop to 14.8 volts.)
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #5
    Are the Voc and Imp numbers from panel specs or as measured?

    If "as measured", the Voc mentioned of 16v could be a panel at nearer normal operating cell temp?
    Off-grid.  
    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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