Difference between inverter kWh output # and meter output #?

HX_GuyHX_Guy Solar Expert Posts: 296 ✭✭✭✭✭✭
in Solar Beginners Corner #1
Is this pretty typical or something that needs to be looked into?

Now that I have an actual meter from the POCO, I can check it against my inverter and again the TED5000 (which has always shows a little less than the inverter). Well, the meter itself actually shows lower than the inverter as well.

SolarEdge Inverter: 53.38kWh
POCO Meter: 51kWh
TED5000: 51.5kWh

I thought maybe the inverter is showing DC kWh and not AC, but they are too close, if that was the case the difference between them would be bigger.
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  • BB.BB. Super Moderators, Administrators Posts: 32,642 admin
    #2
    In general, if your measurements are within ~5%, you are doing pretty well. If they are all within 2%--That is probably about as accurate as you can expect.

    Here is an interesting white paper on Utility meter accuracy:

    http://www.cpsenergy.com/files/Smart_Grid/smart_meters_epri1.pdf

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • HX_GuyHX_Guy Solar Expert Posts: 296 ✭✭✭✭✭✭
    #3
    The meter actually seems to be very accurate, at least backed up by the TED5000 device. It's the inverter that I'm not sure what it's going and why it's showing higher than both.

    Basically my concern is...is there something going on that could be fixed so that 53kWh that the inverter shows makes it to the meter? Or the invert is just inaccuarte?
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  • BB.BB. Super Moderators, Administrators Posts: 32,642 admin
    #4
    Do you know what the line voltage is at the meter vs the Inverter(s) and solar current is?

    For example, if you have 240 VAC at the meter and 250 VAC at the inverter output--That would give you a ~4% line/power loss.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • HX_GuyHX_Guy Solar Expert Posts: 296 ✭✭✭✭✭✭
    #5
    The SolarEdge inverter is reporting an AC voltage of 245.16V while the TED5000, which is inside the main service panel, is showing 121.3V (242.6?). So that's about a 1.1% loss? The run is only about 15 ft, is that normal?

    I can take a multimeter to it later and check actual voltages, but that's what I was able to gather quickly.
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  • BB.BB. Super Moderators, Administrators Posts: 32,642 admin
    #6
    What is the current and the wire gauge?

    Each meter can be easily be off by 0.6% -- So, 1.1% difference is not impossible to explain by meter accuracy.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • HX_GuyHX_Guy Solar Expert Posts: 296 ✭✭✭✭✭✭
    #7
    47.5A (max) and 6AWG wire.
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  • BB.BB. Super Moderators, Administrators Posts: 32,642 admin
    #8
    http://www.calculator.net/voltage-drop-calculator.html

    47.5 amps * 6 AWG * 15 feet @ 240 VAC

    Voltage drop: 0.56
    Voltage drop percentage: 0.23%
    Voltage at the end: 239.44

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • solar_davesolar_dave Solar Expert Posts: 2,392 ✭✭✭✭
    #9
    You are in the realm of noise within the measurements. Mine is much the same, I think the inverters are slightly optimistic. BTW the TED has a multiplier to adjust variability the CT/MTU.
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