Where does my inverter get it's power during low and high insolation?

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wonderfullyrich
wonderfullyrich Registered Users Posts: 2 ✭
in Solar Beginners Corner #1
I've just put in a new small off-grid system.  During the periods of low insolation--say in the morning and evening--my pv panels are obviously not going to be putting out enough to either A. fully power my inverters usage, B. charge the battery.  Say for example that I'm using about 200 watts continuous in the morning and I just looked and see that my charge controller is reporting 100 watts being generated.

Is my assumption that what my inverter is actually doing is pulling the remaining 100 watts required for it's load (assuming no inefficiency for the sake of theory) from the batteries correct?  i.e. If my inverter is pulling a 200 watt load, it's pulling 100 watts from the pv and 100 watts from the batteries.

The same question is true in reverse as well.  If my solar panels are generating 400 watts and that same 200 watt load is on the inverter, is 200 watts actually going to the battery?

Dumb questions perhaps, but I'm trying to wrap my head around it.
Rich
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #2
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    You have it correct.

    The battery is "buffering" the power flow in the system. The battery attempts to hold around 12.7 volts... If the battery bus voltage is >~13.6-14.8 volts, the battery is "charging". If the battery voltage is around 11.5 to 12.7 volts, the battery is discharging.

    The inverter "does not care" where it gets the current (power) from--Battery or solar panels.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • wonderfullyrich
    wonderfullyrich Registered Users Posts: 2 ✭
    #3
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    Perfect! Thanks Bill.
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  • Xizang
    Xizang Registered Users Posts: 50 ✭✭
    #4
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    Years ago railroads had big water towers for their steam locomotives to draw water from.  The trains could drain hundreds or thousands of gallons of water out of those big elevated tanks in just a few minutes time.   The water really came from small wells or springs that refilled those tanks at the rate of maybe only a couple gallons a minute -  far too little flow to be of any use to a locomotive in a hurry.   So the wells/springs slowly recharged those big tanks between steam locomotives stopping for water.
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