|
The over-reporting of energy that Randy refers to below was much higher
than any discrepancy based on monitoring resolution. We have a
pyranometer at the site, and Enphase reported energy production as high
as 38% higher that predicted from irradiance data, as well as 38%
higher than the string inverter portion of the same system. Individual
microinverters showed instantaneous power output as high as 285 W from
a nominal 190 W unit. Enphase explained that there was a software glitch that was resulting in "double counting". It took them over two months to correct this issue, time which is lost from our experimental comparison of string vs. microinverter. They indicated that this seemed to be an isolated situation, but I wonder how many Enphase customers are reporting miraculous performance from their system without verifying via another meter. Screen shot of a day's power production of 22 M190 microinverters (nominal 4180 watts AC):  Mark Mark Westbrock NABCEP Certified Solar PV Installer NM ER-1J Journeyman Electrician Positive Energy, Inc. office: 575-524-2030 cell: 575-640-2432 westbr...@positiveenergysolar.com www.positiveenergysolar.com We
definitely experienced an overstatement.
We have a
client who installed
5kW on a string inverter and 5kW on enphase and it is that side-by-side
comparison that enabled us to positively identify a problem. There was
a
significant overstatement of output. We finally got a Enphase person
who told
us it was a software glitch. The problem appears to be fixed. They
explained to us that our problem was isolated without giving us a
detailed
explanation of what happened. Since that problem was fixed, we have
seen
no difference in output between a string inverter and enphase. Kirpal Khalsa wrote: This same issue has come up over the years for us......first with PV Powered inverters and then noticed in Fronius as well......We have noticed in most of our grid tied systems that are connected thru a "revenue grade meter" for Oregon Energy Trust production reporting, that the inverter always has a higher performance than indicated on the "utility grade meter". We have seen the discrepency as high as 10%. Over time this adds up to significant kWh differences. In our experience the inverter always has the higher kWh reporting, we have attributed this to the inverter wanting to report a good production number, to boost their efficiency claims......maybe even more than is accurate.....I have asked PV Powered and Fronius about this and their line is that to put a "revenue grade meter" into the inverter would be cost prohibitive......interesting as the readily available revenue grade meters are only $30-$60. I would gladly pay that much extra if I didn't have to wire in an additional meter. |
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