Matt,
The Enphase and revenue grade meter are in disagreement by less than
1.1% in the system you are describing - that's good agreement! According
to the Enphase white paper, the wiring loss in the Enphase cabling
between the first and 9th inverter is 0.6%. That only applies to the
last inverter and the average loss for the system will be less, but it
shows that the ac wiring loss is a significant part of the discrepancy.
Also, even the revenue grade meter is not perfect - typically ±0.25%
when new.
Kent Osterberg
Blue Mountain Solar
[email protected] wrote:
Mark,
We have nine Trina modules on our roof with Enphase. Enphase says the
array has produced 2,680 kWh to date. The revenue grade meter 12 feet
away says 2,564. Until I hear otherwise I am reluctant to consider
Enphase reporting precise. It seems to be similar to what I would expect
from a string inverter. I would be delighted to hear more anecdotes
confirming your observations.
Regards,
Matt
Matthew Partymiller
Solar Energy Solutions LLC
(859) 312-7456
[email protected]
Folks,
Has anyone used Enphase monitoring data to get warranty replacement on new
modules with sub par yield?
I have several interesting questions stemming from access to Enphase
module
level monitoring data.
Looking at data from a larger site (80 modules) with no shading issues,
instant power production indicates a high degree of uniformity in panel
power (Sharp NU-U240F1 and D380) easily within 1%.
So what can we now say about the precision and accuracy of this monitoring
data? It seems the old school thinking for string inverters was all the
monitors were 5% off and reporting 5% more power than actual.
Based on the data that I am looking at, it seems the microinverter meters
must be fairly precise and possibly fairly accurate as well. Uniformity of
module performance must also be fairly high.
In any case, this data clearly shows a single module that is not
performing
as well as it's cohorts. For power levels above 50% of STC, it averages 9%
less power than all other modules in the system. So off to Sharp for a
warranty replacement? Yes, but, what if I am 5% low on the report from my
inverter meter and 5% lower on my power from this one module? What if the
module gets back to Sharp and they say it is within spec, now the costs
are
all mine?
Interestingly enough, access to this monitoring data is making more work
for
me as an installer. With a string inverter, I would monitor power
production
readings monthly and be happy so long as yields were higher than what I
projected when I designed and bid the job. Pretty much fire and forget.
Now I am spending time on evaluating this data and doing the work to
change
out the module under warranty and so forth. I am going to end up putting
in
quite a few hours into this for what: to recapture 10% of 1/80 of total
system yield….0.0013%.
I am not complaining, just musing over this interesting evolution.
Mark Frye
Berkeley Solar Electric Systems
303 Redbud Way
Nevada City, CA 95959
(530) 401-8024
www.berkeleysolar.com
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