[RE-wrenches] Enphase performance

[Mark Westbrock]

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 <http://www.oregonsolarworks.com>
> 541-218-0201 m
> 541-592-3958 o
> ------------------------------------------------------------------------
>
> _______________________________________________
> List sponsored by Home Power magazine
>
> List Address: RE-wrenches at lists.re-wrenches.org
>
> Options & settings:
> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
>
> List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
>
> List rules & etiquette:
> www.re-wrenches.org/etiquette.htm
>
> Check out participant bios:
> www.members.re-wrenches.org
>
>   
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20100507/d84ded03/attachment-0003.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: moz-screenshot.jpg
Type: image/jpeg
Size: 10430 bytes
Desc: not available
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20100507/d84ded03/attachment-0006.jpg>