[RE-wrenches] Enphase performance

Fri May 7 18:06:54 PDT 2010

The "Maximum Output Power" listed on the M190 spec sheet is 190 watts.  
Upon observing output exceeding 190 watts, we questioned Enphase tech 
support and were told that the "actual" max output is 199 watts.  
Similarly, the actual max output for the M210 is reported to be 219 
watts, although the spec sheet specifies 210 watts.  This contradiction 
between "specified" and "actual" is troubling, both for proper overall 
system design and proper sizing of overcurrent protection, per 690.8(B)(1).

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

Chris Worcester 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 <mailto: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 <mailto:westbrock at positiveenergysolar.com>
> www.positiveenergysolar.com <http://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
>
>  
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