[RE-wrenches] Enphase performance

Mon May 10 11:36:46 PDT 2010

I just don't understand why going over 20 percent of module nameplate to
nameplate inverter rating makes any sense.

I regularly see 120-130 percent of nameplate amperage coming off of the
array on our office due to edge of cloud.

So I have to disagree with Dana in this instance.  I see this a bad design
especially since lower output mods are so readily available these days.

And what's up with the Enphase 210?  Doesn't it say on their latest
compatibility list (March 2010) that it's only good for the Sanyo line?
What's up with that especially since I know that one other manufacturer is
signing off on using the Enphase 210 with their 210-watt module, apparently
with Enphase's approval?

Marv-why is your Enphase 210 only listed for use with the Sanyo line when
there's a growing number of 210+ watt mods out there these days?

Thanks,

marco

I've been concerned about pairing higher wattage modules (~230W) with the
190W Enphase fearing a lot of clipping and power loss when the modules are
at full power. 

I did some modeling of this setup in PVSYST and found that the expected loss
from the inverter being underpowered is 0 - 0.2% annually depending on the
assumptions. The modeling was for northwestern Washington State. A fifth of
a percent seems pretty negligible to me and is easily offset by removing
module mismatch from the equation. So, I'm convinced that matching modules
in the 230W range with the 190W Enphase inverters is a good design.

I recently installed 4kW of 230s with the Enphase 190s and have seen their
output as high as 199W. 

Dana

Dana Brandt
Ecotech Energy Systems, LLC
www.ecotechenergy.com
dana at ecotechenergy.com
360.510.0433

On Fri, May 7, 2010 at 4:48 PM, Chris Worcester <chris at solarwindworks.com>
wrote:

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):
Error! Filename not specified.

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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