Hi Jason,
I went back and forth bunch of times with Enphase in late 2020 or early
2021 on this very issue. Maybe Nick can weigh in if my information is
out of date, but what I found is that Enphase uses a 15 minute net data
register for energy import/export in their Envoys system monitor, rather
than properly recording imported and exported energy in separate
registers. A strange engineering/software engineering choice!
What this means is that for any 15-minute period where there is both
imports and exports, only the net import/export is reflected in the
consumption monitoring.
For example, lets say a PV system is exporting 3,000 W above the base
load of the house for the full 15-minute measurement period, but an air
conditioner turns on drawing 7,000 W for 5 minutes (net import of
4,000W). Real exported energy is 3,000 W for 10 minutes, or 500 Wh. Real
imported energy is 4,000 W for 5 minutes, or 333.3 Wh. But Enphase is
just going to show 166.7 Wh exported for that time period, not
reflecting the imported energy.
So the only utility meter configuration where the Enphase consumption
monitoring is actually accurate would be a meter that also uses a
15-minute net register for imports/exports. Here in Arizona, all our
utilities use revenue meters with separate two instantaneous
accumulating registers for both import and export, so we have seen
discrepancies similar to what you're seeing.
Back in 2020, I verified all this was the case by using eGauges on a
couple of systems to measure import/export on a 1-second basis. If
helpful, could dig back into that analysis--let me know off-list.
If the customer has access to hourly energy use data from their utility
to compare, they'll see that the Enphase consumption data is accurate at
night, when there is no exports, or for periods where the system is
continually exporting energy for a 15-minute period.
We install Enphase pretty much exclusively, but it's still a bit of a
thorn in my side that this hasn't been fixed, to my knowledge.
Best,
Louis Woofenden
Engineering Director/Owner
Net Zero Solar
945 W Silverlake Road, Tucson, AZ 85713
Arizona ROC #248710, 259756, 259521
Jason Szumlanski via RE-wrenches wrote on 10/27/22 8:59 AM:
I received this question from a non-client:
/On a daily basis, FPL [Florida Power and Light] (per their app)
consistently shows a 20 to 40% (higher) difference in what they
delivered and received vs what Enphase app shows as imported and
exported. My installer can not explain why. Any ideas?/
Incidentally, I have noticed issues with this. The import and export
figures don't seem to match up. I'm wondering if it could be time zone
issues or just the accuracy or sampling frequency. Even over longer
timeframes the data does not line up with utility figures.
(Yes, all circuits are being monitored in these cases)
Any thoughts?
Jason Szumlanski
Florida Solar Design Group
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