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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.<br>
<br>
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.<br>
<br>
Screen shot of a day's power production of 22 M190 microinverters
(nominal 4180 watts AC):<br>
<img src="cid:part1.04080804.05040506@positiveenergysolar.com" alt=""><br>
<br>
Mark<br>
<pre class="moz-signature" cols="72">Mark Westbrock
NABCEP Certified Solar PV Installer
NM ER-1J Journeyman Electrician
Positive Energy, Inc.
office: 575-524-2030
cell: 575-640-2432
<a class="moz-txt-link-abbreviated" href="mailto:westbrock@positiveenergysolar.com">westbrock@positiveenergysolar.com</a>
<a class="moz-txt-link-abbreviated" href="http://www.positiveenergysolar.com">www.positiveenergysolar.com</a></pre>
<br>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);">We
definitely experienced an overstatement.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);">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.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);"><o:p> </o:p></span></p>
<span style="color: rgb(31, 73, 125);">Randy<br>
<br>
</span>Kirpal Khalsa wrote:
<blockquote
cite="mid:u2te925cf121005070938n23c063a9q9595ad771e737659@mail.gmail.com"
type="cite">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. <br>
I don't think this problem is unique to the Enphase units (i haven't
installed any of these), I think all inverters should be required to
install the revenue grade meters to give accurate reporting of actual
production. Similar to how states have a "weights and scales"
accuracy certification, energy consumption and production meters should
be similarly calibratable. <br>
<br>
-- <br>
Sunny Regards,<br>
Kirpal Khalsa<br>
NABCEP Certified Solar PV Installer<br>
Renewable Energy Systems<br>
<a moz-do-not-send="true" href="http://www.oregonsolarworks.com">www.oregonsolarworks.com</a><br>
541-218-0201 m<br>
541-592-3958 o<br>
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