[RE-wrenches] Enphase performance

Mon May 10 11:57:22 PDT 2010

Something to remember is that my simulation was for a specific location in
Washington. The answer might be different for your location and weather
patterns.

I agree that it seems wrong to have the inverter rating 20% less than the
array nameplate. Typically, I would consider that sort of pairing a poor
design. You're right that there will certainly be some clipping - especially
with cloud-edge effects. The real question in my mind is not whether the
inverter will ever clip the output of the array, but what's the real impact
of that on energy generation on an annual basis. This is what lead me to do
the modeling simulations which indicated the effect is negligible when taken
in the context of the total annual production. Compared to the whole year's
sun, there just isn't that much energy in high production spikes like cloud
edge effects that the inverters will clip - at least not around here.

One thing to consider is that if you go with smaller modules you need more
inverters. You might compare the cost of the additional inverters to the
value of the 0.2% energy loss from clipping over the lifetime of the system.

Dana

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

On Mon, May 10, 2010 at 11:36 AM, Marco Mangelsdorf <marco at pvthawaii.com>wrote:

>   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
> 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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