[RE-wrenches] Enphase performance

Fri May 7 16:48:54 PDT 2010

Do the Enphase inverters clip the output power to their rating like other
manufacturer's? So a M190 can only put out 190 watts max? I have had this
question for a bit now on system performances using Enphase in designs
during our cold spring and fall days.

Sincerely,

Chris Worcester

Solar Wind Works
NABCEP Certified PV Installer
Phone: 530-582-4503
Fax: 530-582-4603
www.solarwindworks.com <http://www.solarwindworks.com/> 
chris at solarwindworks.com
"Proven Energy Solutions"

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Mark
Westbrock
Sent: Friday, May 07, 2010 10:33 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] Enphase performance

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
westbrock at 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.

Randy

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.  
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.  

-- 
Sunny Regards,
Kirpal Khalsa
NABCEP Certified Solar PV Installer
Renewable Energy Systems
www.oregonsolarworks.com
541-218-0201 m
541-592-3958 o

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