Meter Reading doesn't match Inverter

System
System Posts: 2,511 admin
in PV Installers Forum - NEC, Wiring, Installation #1
Wanted to know if anyone else has seen this type of issue. I installed a 3.78k system in November with an SMA 4000W inverter. Here in pennsylvania we are required to install a customer meter between the inverter and the Panel box for the customer to monitor there AC production. Now after only 2 months of production the Itron digital meter is 6kWh less than the total production that is being shown on the Inverter display. It seems to be increasing as a month ago it was at 3 or 4 kWh. Any suggestions would be greatly appreciated thanks.
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #2
    Re: Meter Reading doesn't match Inverter
    gelderdog wrote: »
    Wanted to know if anyone else has seen this type of issue. I installed a 3.78k system in November with an SMA 4000W inverter. Here in pennsylvania we are required to install a customer meter between the inverter and the Panel box for the customer to monitor there AC production. Now after only 2 months of production the Itron digital meter is 6kWh less than the total production that is being shown on the Inverter display. It seems to be increasing as a month ago it was at 3 or 4 kWh. Any suggestions would be greatly appreciated thanks.

    Well assuming your making 12kWh day, for 60 days is ~700kWh , if your difference is 6kWh that's 0.8% difference, pretty darn close
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,714 admin
    #3
    Re: Meter Reading doesn't match Inverter

    If they agree within 2% to 4%, you are within the margin of error for two revenue grade meters.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #4
    Re: Meter Reading doesn't match Inverter
    gelderdog wrote: »
    Wanted to know if anyone else has seen this type of issue. I installed a 3.78k system in November with an SMA 4000W inverter. Here in pennsylvania we are required to install a customer meter between the inverter and the Panel box for the customer to monitor there AC production. Now after only 2 months of production the Itron digital meter is 6kWh less than the total production that is being shown on the Inverter display. It seems to be increasing as a month ago it was at 3 or 4 kWh. Any suggestions would be greatly appreciated thanks.
    That's what, about 50 cents over a couple of months? Less than 1 cent a day?

    'Fess up; you are an engineer, aren't you? ;^)
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  • NEOH
    NEOH Solar Expert Posts: 74 ✭✭
    #5
    Re: Meter Reading doesn't match Inverter

    gelderdog,

    What is your total KWH production and for how many days?
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  • solarvic
    solarvic Solar Expert Posts: 1,072 ✭✭✭✭
    #6
    Re: Meter Reading doesn't match Inverter

    Couple of questions? I am in Western Pa. and have penn power which is part of First Energy. I got my system installed late december of 2009 and didn,t have to have my own meter but put one in anyway. Foreman of the meter dept ask me why I had my own meter? I told him so I knew how much power I would make over time. He told me it wouldn,t match anyway. They were using 2005 nec standards in late 2009. Are they still using 2005? Getting my system to pass inspection was just a formality. inspector and my electrician never did a solar system before, so I gave the inspector a tour and explained how everything worked. He checked meter to see if it was wired right and I got it passed.
    :Dsolarvic:D
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #7
    Re: Meter Reading doesn't match Inverter
    solarvic wrote: »
    Couple of questions? I am in Western Pa. and have penn power which is part of First Energy. I got my system installed late december of 2009 and didn,t have to have my own meter but put one in anyway. Foreman of the meter dept ask me why I had my own meter? I told him so I knew how much power I would make over time. He told me it wouldn,t match anyway. They were using 2005 nec standards in late 2009. Are they still using 2005? Getting my system to pass inspection was just a formality. inspector and my electrician never did a solar system before, so I gave the inspector a tour and explained how everything worked. He checked meter to see if it was wired right and I got it passed.
    :Dsolarvic:D

    i don't see what the nec version has to do with wattage measurements and could you be more specific on what you mean in reference to the meter matching what?
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  • drees
    drees Solar Expert Posts: 482 ✭✭✭
    #8
    Re: Meter Reading doesn't match Inverter

    I suspect that the inverter isn't accounting for it's "vampire draw" or power it pulls when the system is not generating electricity.

    Anyway, like the others said - withing 1% is actually VERY good.
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  • solarvic
    solarvic Solar Expert Posts: 1,072 ✭✭✭✭
    #9
    Re: Meter Reading doesn't match Inverter
    niel wrote: »
    i don't see what the nec version has to do with wattage measurements and could you be more specific on what you mean in reference to the meter matching what?
    The poster said he was from Pa. also and got his system connected late in 2010. I got mine connected late 2009.Been thinking about growing my system some and I wondered if Pa is still using nec 2005 or if the moved to a later version which probably has more red tape to go thru. I wasn,t required to have my own personal meter as poster said he was required to have. I chose to have a personal meter to keep track of my output at the inverters before entering power suplyers meter. The woman that installed the power company.s meter couldn,t understand why I had my own meter and ask me where I got it ect. and a bunch of other stupid questions and called her boss on phone. Then her boss wanted to talk with me questioning me why I had my own separate meter ect. He told me that thier meter readings and mine wouldn,t be the same anyway. I kind of think Penn Power is still on a learning curve as my bills get changed , reisued ect. Still waiting for bill that was read dec.24. Getting close to next meter reading time. I used to have automatic billing but had to change to old fashion bill in the mail because thier software doesn,t suport renewable energy. Solarvic:D Guess I should have addressed to original poster about the question about which nec Pa is using. I thought it might help me as Pa. has Statewide building codes now.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #10
    Re: Meter Reading doesn't match Inverter

    i guess i should state that pa doesn't adopt standards as that is up to local areas to accept or not.
    i still do not know why their meter and your meter should differ in wattage measurements. or is it a case of theirs being net wattage while yours only indicates outgoing from your solar?
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  • solarvic
    solarvic Solar Expert Posts: 1,072 ✭✭✭✭
    #11
    Re: Meter Reading doesn't match Inverter
    niel wrote: »
    i guess i should state that pa doesn't adopt standards as that is up to local areas to accept or not.
    i still do not know why their meter and your meter should differ in wattage measurements. or is it a case of theirs being net wattage while yours only indicates outgoing from your solar?
    Niel, I got to thinking why the meter readings might not match. I have a meter at the inverters so I know what they make. I have a mobilehome service. Power from the inverters go into bottom of service box and out the top to home. Power co meter only measures electric going into grid or coming from grid. So if I am using most of my power in the home the power co meter would only measure eccess power that I wasn,t using or if I was making less than I needed power co meter would measure that amount. So power co meter and my meter probably would never agree with eadh other. Am I correct in this evaluation? :Dsolarvic:D
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #12
    Re: Meter Reading doesn't match Inverter

    ok, i understand now as they are measuring different aspects of the system and will differ.
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  • System2
    System2 Posts: 6,290 admin
    #13
    Re: Meter Reading doesn't match Inverter

    Sorry I didn't respond to this sooner but yes this all makes sense as I was leaning to the fact that the inverter does need or use some power to operate but that its Production reading probably is before that happens. Secondly the Meter is a State Rebate requirement not for inspection or NEC or anything like that. I couldn't figure out why they required it when all Inverters give you a reading or allow to access those readings anyway.
    Secondly this was manly an issue for my customer because the SREC reading that she has to turn in comes from that meter so it is going against her SREC's. But now it sort of makes sense because the inverter is not calculating its power used which should not be counted towards SREC's. Thanks again for everyone's input.
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  • arcturusk1
    arcturusk1 Solar Expert Posts: 26 ✭
    #14
    Re: Meter Reading doesn't match Inverter

    I'm actually a big fan of putting what we would call a "solar production meter" either before or after the PV AC Disconnect (doesn't really matter where). Well, to be fair, it's required here in OH on all systems over 6kW anyway. A solar production meter allows me to get very accurate measurements on what our systems are doing. It also helps a ton when I need to report the generation to the GATS system so I can get certificates created; it's basically a no-BS method because if you ever need to verify to GATS that you truly have generated X amount, all it takes is a quick picture of the meter and you're good to go. Besides, what good engineer wouldn't want detailed data on his systems? :p

    Note: I've had GATS lock down a generator before because they thought I was misreporting the output (it was doing very well). I took a picture, emailed it off, and got the problem resolved.
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