Netmetering discrepancy

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geeck
geeck Registered Users Posts: 5 ✭
in General Solar Power Topics #1
I have a 10.2kw Xantrex system in operation since last August. I'm waiting for a years worth of data before jumping in with both feet with the local utility. My problem is, what the Xantrex software says and what I'm getting credited for is very much out of sync... in the power companies favor of course. I have almost 2 years of data before the Install and after I get a full year with the Array I will crunch the numbers and approach the power company. Something is real fishing.

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  • TheBackRoads
    TheBackRoads Solar Expert Posts: 274 ✭✭
    #2
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    Re: Netmetering discrepancy

    Ever thought about getting a TED to measure your usage and solar production?

    http://www.theenergydetective.com/ted-5002-g


    Edit: Welcome BTW!!
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #3
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    Re: Netmetering discrepancy

    How much is it off? Some inverter manufacturers are less than accurate on their data, and the TED if setup properly is about 1% accurate. Of course it all depends on method of collection like the meter is a 30 sec sample and TED is a 2 sec sample and the inverter is a 5 minute sample.

    I think you might have a tough row to hoe, against the Utility, but if you have some data that says it is off like 10% go for it.
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #4
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    Re: Netmetering discrepancy

    The Xantrex is gross production, the utility meter is net usage, they are two different values.

    Your home consumes some or all of the solar production throughout the day and the utility meter does not have a means ( or need ) to record that generation used.
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  • solarix
    solarix Solar Expert Posts: 713 ✭✭
    #5
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    Re: Netmetering discrepancy

    Probably not the problem in your case, but I have seen actual cases where the utility installed the wrong net-metering revenue meter and the customer was actually getting charged for the excess generation instead of getting credit.
    It is good to have your own kWHr meter on your solar system to show your total production since the utilities pretty much don't trust inverter data. Since it is not for revenue use you can get regular mechanical kWHr meters very inexpensively as rebuilt units from Hialeah Meter in Florida.
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  • mr.radon
    mr.radon Solar Expert Posts: 158 ✭✭✭✭✭
    #6
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    Re: Netmetering discrepancy

    I have EcoDog, TED 100, Enphase and my utility meter.
    Enphase reads 2.4% more then Production Meter.
    TED reads about 3.8% more then production meter.
    EcoDog reads 1.4% more then Production meter and 3.4% less then NetMeter (Grid consumption) 2.0% less then NetMeter (Grid export).

    Utility is always getting the stats in their favor.

    Maybe its just a random trend? :roll:
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,457 admin
    #7
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    Re: Netmetering discrepancy

    Utility meters are around (supposed to be) 2% or better accuracy, if I recall correctly.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • SkiDoo55
    SkiDoo55 Solar Expert Posts: 414 ✭✭✭
    #8
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    Re: Netmetering discrepancy

    Your Zantrex built in Production meters should be fairly accurate as they are Calif CEC listed for accuracy. As Solar Guppy says they report the production of the inverter not you net ussage. A TED5000C will give you a sanity check on production and usage with result of net usage.
    You could also take the monthly inverter production add the monthly utility meter reading and compare to your historical data to see if it reasonable to what you have consumed in the past. Consider any engery efficency measures or additional loads that have been added or life style changes.
    Is your utility meter still analog(dial) or digital display. Turn most everything off mid day and watch bother meters and see if the are close in registering production vs: what is coming off of utility meter. Time for an hour and compare?
    GT3.8 w/4600W Trina 230W, TX5000 w/5000W ET-250W, XW4024 w/1500W ET-250W, 4 L16, 5500W Gen. (never had to use) Yet!!
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #9
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    Re: Netmetering discrepancy

    solar guppy nailed your discrepancy.
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  • geeck
    geeck Registered Users Posts: 5 ✭
    #10
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    Re: Netmetering discrepancy

    I am talking way off, not 10%, for example last April 2010 (pre-install) I used 1326kwh.

    This April 2011 (post -install) has been milder 6 to 8 Degrees cooler on avg. than last year. We live in the Deep South, so the Air Conditioning (which is our biggest load) was only used sparingly.

    This month the utility company said I used 1034 kwh the Xantrex monthly log for April shows I produced 1269.5 kwh

    So if it was cooler this April and the HVAC did not run as much. How did I consume 1269.5 + 1034 for a total of 2303.5

    SO I SAY Whiskey Tango Foxtrot:grr
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  • SkiDoo55
    SkiDoo55 Solar Expert Posts: 414 ✭✭✭
    #11
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    Re: Netmetering discrepancy

    As stated by Solar Guppy sounds like the Utility meter is not measuring what you deliver back to the grid it is either a ratched meter for the dials or they set the digital meter up to only record delivered (Grid) power. What type of utility meter is installed analog or digital?
    GT3.8 w/4600W Trina 230W, TX5000 w/5000W ET-250W, XW4024 w/1500W ET-250W, 4 L16, 5500W Gen. (never had to use) Yet!!
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,457 admin
    #12
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    Re: Netmetering discrepancy

    Geeck,

    I assume you have one utility meter and the one kWH meter on the Xantrex?

    And that you have the permits/utility approval to connect a Grid Tied Solar system?

    Next, watch your utility meter at night and during the day.

    Does the meter run "forward" at night, and "backwards" during the day (do the kWH number count "up" at night and count "down" during the day) when you have more solar power than loads (i.e., major loads like AC, microwave, electric stove, off)?

    There are times utilities have installed the wrong meters. The new electric meters can be programmed to always count "up" to protect against people running the meters backwards (i.e, you consume 1 kWH, you pay for it. You generate 1kWH pushed back to the utility, you pay for that too). Other meters will not spin backwards (mechanical or electronic)--also to protect their revenue.

    Also, in rare cases, the meters have been miss-programmed. The meters may have a shunt correction in them (typically for large businesses)--In a few cases, the utility programmed a "shunt" value in the meter which made it read "fast".

    In our area, we are changing to "smart" meters--Turned out there was one vendor that had a thousand+ bad meters that ran "fast" during hot sunny weather (i.e., during A/C season)--Took the utility a year or more to figure that one out--even though the meters were sending "error codes" back to the utility.

    PG&E finds heat related defect in 1600 SmartMeters | abc7news.com

    Does your meter read Watts on its display (many new meters will flash the current watts every few seconds). Mine also includes an arrow showing the direction of power flow (right, I am consuming power; left, I am generating power).

    Also, there is the mechanical disk (old meters) and some newer meters have a bar graph that simulates the rotation of the mechanical disk. You can read the value from the face of the meter, and time the rotation with a stop watch to quickly read your present power consumption/generation (at least what the meter thinks it is).

    I believe the Xantrex is supposed to be around 2% accuracy (very good) for its power meters. With most of the load off in your home, you should be able to confirm X kWatts out from the Xantrex is spinning/logging X kWatts at the utilty meter (my home takes around 100-300 watts with everything off except the fridges/freezer).

    So--you should get a good idea (down to the 0.1 kW level or so) how close the GT inverter and the Utility meter agree.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #13
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    Re: Netmetering discrepancy
    geeck wrote: »
    I am talking way off, not 10%, for example last April 2010 (pre-install) I used 1326kwh.

    This April 2011 (post -install) has been milder 6 to 8 Degrees cooler on avg. than last year. We live in the Deep South, so the Air Conditioning (which is our biggest load) was only used sparingly.

    This month the utility company said I used 1034 kwh the Xantrex monthly log for April shows I produced 1269.5 kwh

    So if it was cooler this April and the HVAC did not run as much. How did I consume 1269.5 + 1034 for a total of 2303.5

    SO I SAY Whiskey Tango Foxtrot:grr

    SO they billed you for what 1269? it certainly does sound as if something is up. Have you observed the meter running backward (or on digital meter the arrow going the other way?)

    What did the power company say to all of this?
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  • geeck
    geeck Registered Users Posts: 5 ✭
    #14
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    Re: Netmetering discrepancy

    I have a "Itron" Digital Watt meter supplied by the utility. There is a directional bar that shows direction of flow and it does go in reverse during the day.

    1326 kwh     Last Aprils usage (before Solar install)

    1269.5 kwh     This Aprils production report from Xantrex (YES I KNOW THIS IS GROSS NUMBERS)

    1034 kwh This Aprils Utility bill KWH I had to pay for. (for cooler than usually month)

    I also have a "Brand Electronic" Solar power meter (It's a POS) and hasn't worked very well. I was hoping to verify numbers with it

    It's all 100% legit and inspected

    Power company pulls a Sgt Schutz ( I knows nothing!!!)
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,457 admin
    #15
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    Re: Netmetering discrepancy

    It looks like your meter is either not turning "backwards" or it is only turning forward no matter which direction the power is flowing...

    Pick a time during a sunny day. Turn off all loads / TV / etc... If you want, leave the refrigerator/freezer(s) plugged in.

    Note the reading on the meter... You may have several "registers" (time of use, power used, power generated, etc.) depending on your billing plan.

    An hour later, read the register(s) again. Did the readings go up or go down. With a 10kW system--your numbers should "go backwards" by 7-8 kWHrs on a nice clear/sunny day pretty easily. Do the same thing at night (or hit the Xantrex disconnect) and read the meter again an hour later (may use 1-3 kWHrs, or even less). Turn on the A/C (with Xantrex shut down still) and see how much power you use in the next hour. Make sure the number count-up/cound-down in a sensible manner.

    Also--it may seem silly, but double check the serial number on the meter and your electric bill. Also, confirm your bill's register readings are similar to your meter's... Another poster here had the utility assigning the wrong meter to his account (duplex or something).

    Lastly, if this is a condo/town-home. It would not be impossible that power is miss-wired and some circuits go to the wrong meter (I have seen this in a small commercial complex--electrician adding AC connected to the wrong meter).

    Don't take anything for-granted right now--Make sure you understand your meter's reading(s) and how they relate to your billing.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • geeck
    geeck Registered Users Posts: 5 ✭
    #16
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    Re: Netmetering discrepancy

    The only thing the ITRON meter shows is the direction of the power and the "NET" number.

    I was yearly averaging around 1300 kwh a month before the install (more in Summer / less in winter) The meter has been in for 8 months Sept-April and the NET usage on the meter shows almost 9000 KWH (with no real summer months in the avg) a little over 1000 kwh per month avg for the 8 months the meter has been installed.

    Meter number matches the number on the utility bill.

    The array is for a single family dwelling
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,457 admin
    #17
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    Re: Netmetering discrepancy

    Say, your meter goes from 20,123 to 21,123 kWH for a month (1,000 kWH per month).

    In the middle of the day, when your A/C is turned off, no well pumping, etc., read it at 11 am and again at noon... Looking for the numbers to either (assuming your power usage is low, and your GT pumps out 8-9 kW or kWH from 11-noon):
    1. 20,123 -> 20,115 = -8 kWH generated
    2. 20,123 -> 20,123 = +0 kWH logged (does not turn backwards)
    3. 20,123 -> 20,121 = +8 kWH generation logged as billed power (always turns forward)
    Anyway--That is were I would start.

    And at night, you should see the kWH number always going "up" (20,123; 20,124; 20,125; etc.).

    -Bill

    PS: #1 is the way I would assume the meter should work--if everything is correct.

    You do not have any special Time of Use or anything other than a net bill--correct?
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,457 admin
    #18
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    Re: Netmetering discrepancy

    Also, confirm that the 20,123 kWH on the meter matches (wihin 1,000 kWH or so) your current meter reading (current - last month reading = kWH used last billing cycle).

    Many (most?) people years ago had their first bill or so done wrong. The billing computer was designed not to log "negative power use" (generation) and would simply add 100 or 1,000, or 10,000 kWH to the meter reading assuming that the meter reader got a digit wrong.

    My first bill was $184 for the first two weeks or so--with GT solar... When our electric bill had never been more than $60 a month. Wife was not thrilled. Utility asked us what we thought we owed and let us pay that (minimum bill--we are net generators except for the few months in winter).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • geeck
    geeck Registered Users Posts: 5 ✭
    #19
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    Re: Netmetering discrepancy

    All of what you say makes sense I was hoping for an easy fix. Something has got to be wrong there is no way the power company's billing is correct. I'm going to try and get that "Brand Electronics" power meter working too maybe it will help verify some numbers.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,457 admin
    #20
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    Re: Netmetering discrepancy

    I think your kWH logging is far enough off that you should see it based on the simple tests I suggested. I would not worry about the power meter at this time--I think you will see something obviously wrong.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Frxddy
    Frxddy Solar Expert Posts: 113 ✭✭✭✭
    #21
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    Re: Netmetering discrepancy

    As mentioned, you may be using some power as it is produced. Any power used while the sun is out does not show on the power company meter. I didn't notice the cost of a TED, but for $25 I bought an electric meter on eBay & any home generated power goes through it before it goes to use or grid. That was I know what I produced (as accurately as that meter at least). When I had my wind turbine working I used about half the power as it was produced & the other half went to the grid.
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #22
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    Re: Netmetering discrepancy

    geeck,

    With a system that large, the only way your bill could be only down 300kw compared to the previous year is two things

    Your using more energy than you realize, water heaters, pool pump, clothes dryer, refrig in the garage ect

    Or

    You meter is counting the exported energy as energy imported, or another way of saying this is you being billed for the energy you sell instead of credited ... It not that uncommon of a screw up as this is the default way meters work to prevent theft.

    All you have to do it the one hour check BB mentioned, turn off all large appliances at the breaker panel ( pool ups, dryers, water heaters ) , write down the reported kwr on the meter, wait one hour, write down the numbers again. At solar noon, you should see the numbers drop between 4-8kwh. If you see the number increase, then the utility never programed the meter right.

    You don't need to do anything else but this test and you will know your answer, since you have a 10kw system, the only logical explanation is the utility meter never got re-programmed or that meter can't do net metering which again is common. I have a special dual register meter proved by the electric company just for this reason

    What is the model of the meter and who is your electric company?
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #23
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    Re: Netmetering discrepancy

    I had the same situation with my Utility Company with the first Net Bill. The computer program that computes usage was figuring it right , but the billing program that printed the bill was doing something totally different in what it billed and printed. It only took a call to get it worked out, that said, they are pretty adamant that there is only one meter that counts, THEIRS.
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #24
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    Re: Netmetering discrepancy
    Blackcherry04 wrote: »
    I had the same situation with my Utility Company with the first Net Bill. The computer program that computes usage was figuring it right , but the billing program that printed the bill was doing something totally different in what it billed and printed. It only took a call to get it worked out, that said, they are pretty adamant that there is only one meter that counts, THEIRS.

    Yep APS is the same way, it is what their meter says that counts, but they still require a reporting on a postcard once a year from my production meter for sanity check to determine what the solar actually produces, I suspect for the REC that they own because of the $3 rebate they provide.

    Nothing wrong with trying to keep them honest. They have swapped my meter about 3 time in 18 months, I think they look at a negative peak balance every month and figure something is up. ;) Even with all our solar capacity we still buy some off peak every month, so far it has been a couple dollars worth per month this year, but that will change when we need to run the AC all night.

    I like external measurement for getting a handle on the load side. It has helped to determine where to take action to keep it all under control.
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  • Jburgess
    Jburgess Solar Expert Posts: 130 ✭✭✭
    #25
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    Re: Netmetering discrepancy

    They put a smart meter on my production as well as my net, which is read daily.

    Utilities billing systems are not always solar friendly.

    You can imagine my surprise when I saw this $7142.43 balance on my account:

    srpbalance4.jpg

    Their software assumed because the off peak reading was lower than the previous month I had rolled the meter over and billed my for around 99,500 off peak KWh.

    A quick call got it changed to KWh credit and a total bill of $10
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  • russ
    russ Solar Expert Posts: 593 ✭✭
    #26
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    Re: Netmetering discrepancy

    Not nice to confuse the nice peoples poor computer!:p
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  • System2
    System2 Posts: 6,290 admin
    #27
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    Re: Netmetering discrepancy

    My suggestion is to get a single phase power meter commercial grade if you can install it yourself ie a shark meter with the software they communicate modbus
    but come with their own softrware that you can connect to your pc and are less than 300.00 dollars from an electrical supply house and store all kinds of trend data you can refute the power co billing:cool:
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  • System2
    System2 Posts: 6,290 admin
    #28
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    Re: Netmetering discrepancy
    dlhvac wrote: »
    My suggestion is to get a single phase power meter commercial grade if you can install it yourself ie a shark meter with the software they communicate modbus
    but come with their own softrware that you can connect to your pc and are less than 300.00 dollars from an electrical supply house and store all kinds of trend data you can refute the power co billing:cool:

    http://www.electroind.com/shark.html
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