Solar Enphase app versus electrical meter
KMB01915
| Posted in General Questions on
Should my outside electrical meter (new meter that was installed before solar was turned on) match the consumption shown on my Enphase app? When my solar system was turned on, my new meter read “0” and so did the app. As time has gone on (solar turned on in November), the app and the meter are getting further apart. At one point I noticed a 4-5 kWh difference (the meter reading higher) and now it’s up to a 9 kWh difference. The Enphase app reads 21.8 kWh Net Imported while at the same time the meter reads 30 kWh. I feel like the app and the meter are just calibrated slightly differently? Has anyone else experienced this? Thank you!
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
Unless you're using the Enphase for calculating net metering or SREC's, it's not going to be "revenue quality," which means super accurate. It will probably be plus or minus a few percentage points. The meter has to be revenue quality and is what your billing is going to be based on.
Most states regulate the utilities and require that the meters be calibrated. The usual tolerance is in the -x% to +0% range. What that means is that there is supposed to be NO error in the "sold you more power than you actually used" direction, any error is supposed to be on the side of being favorable to the customer. I'd be very surprised if the utility meter is overbilling you, but it IS possible. You would need to check with a CALIBRATED watt hour meter, which the Enphase probably isn't.
It also makes sense the the apparent error here would grow over time, because watt-hours are cumulative, which means any small amount of error will compound over time, building up to larger and larger apparent differences between the two. If you're seeing that few-kW/h difference over a period of months, it's probably not a big deal, and is just the result of the meters not being in agreement, which means one, or both, of the meters is out of calibration. This probably isn't something really worth worrying about if it's only a small percentage difference. I usually think of "wihin 5%" as pretty good for electrical stuff, since most component tolerances aren't any better than 5% anyway.
Bill
Although the absolute error would grow over time, the relative error would stay the same. That is, if there was a 5% difference in measured Watts, the difference in kWh would also be 5%. The OP is reporting a difference of more than 25%, which seems to be well outside the bounds of normal tolerance.
That's a large error. One possibility is that the Envoy consumption CTs are not placed correctly. For example, if they were placed on a subpanel rather than the service panel they would miss part of the load.
Envoy has a video about consumption CTs that you might find helpful.