[RE-wrenches] Accuracy of Enphase consumption monitoring

[Louis Woofenden]

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out of date, but what I found is that Enphase uses a 15 minute net data 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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