> I have REC 215 on Enphase 190. I see a lot of clipping. Every sunny > day in the > winter and spring.
What angle is your array? Where is it located? What I am seeing may be regionally specific. I have seen some clipping, but usually the inverters have some overhead left from the 199 W limit. With the 30 degree angle, even on sunny days with snow on the ground the inverters max out it the high 180s. On another system in the area (with a string inverter)the roof pitch is 45 degrees. The array can peg the inverter on those days. The inverter and the STC rating of the modules are a perfect match. > > > > > > ________________________________ > From: Drake <drake.chamber...@redwoodalliance.org> > To: RE-wrenches <re-wrenches@lists.re-wrenches.org> > Sent: Thu, January 20, 2011 8:23:55 AM > Subject: Re: [RE-wrenches] Inverter oversizing > > On a couple of Enphase systems I monitor regularly, the modules are > oversized > compared to the inverters. One system has Sharp 224 W modules and M-190s > (capable of producing 199 W). The array is a ground mount at a 30 degree > tilt > at 39+ degrees latitude. > > > When the system was new in the autumn, I noticed two days of some > clipping. > Since then, none. In the summer, when the sun angle is better, the heat > will > keep the wattage down so clipping will very seldom occur. The modules > will not > be close to STC, so the inverters should not be pushed to their maximum. > > The same is true of string inverters. Since real power of the modules in > generally significantly below the nameplate, inverters will generally not > run at > maximum power.  When we take in all the factors affecting the actual > array > power, I think that 120% over sizing from nameplate wattage is generally > safe. > > > Drake > > > At 09:14 PM 1/19/2011, you wrote: > > David, >> >>Thanks for sharing that paper. The labeling the graphs for the >> 10-second and >>1-minute data in Freiburg appears to be reversed - the one minute >> averaging >>seems to have more data in all of the bins above 1000 W/sq m. >> Basically, these >>graphs show that irradiance observations above 1100 watts per square >> meter are >>fleeting and disappear in hourly averages.  Such occurrences are also >> masked to >>a small extent by 1-minute averages. >> >>Kent Osterberg >>Blue Mountain Solar, Inc. >> >> >> >>David Brearley wrote: >> >>This reminds me of a scholarly article I came across about a year ago >> while >>doing some research. Hereâs a link to it if anyone is interested: >>> >>>www.lepten.ufsc.br/publicacoes/solar/eventos/2005/PSC/burger_ruther.pdf >>> >>>David Brearley, Senior Technical Editor >>>SolarPro magazine >>>NABCEP Certified PV Installer ⢠>>>david.brear...@solarprofessional.com >>>Direct: 541.261.6545 >>> >>>On 1/19/11 12:29 PM, "Bill Brooks" <billbroo...@yahoo.com> wrote: >>> >>> >>>Kent, >>> >>> >>> >>> >>>How often were your data records? To capture edge of cloud effects, you >>> need >>>one-second data. Not many people gather that fast or that much data on >>>inverters. I donât think there is that much energy in these spikes, >>> but they are >>>real and make some difference. 15-minute average data will completely >>> wash out >>>this data. >>> >>> >>> >>>This is also a deficiency in modeling software since most models are >>> using >>>hourly data. >>> >>> >>> >>>Bill. >>> >>> >>> >>>From: re-wrenches-boun...@lists.re-wrenches.org >>>[mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Kent >>> Osterberg >>> >>> >>> >>>Sent: Tuesday, January 18, 2011 1:18 PM >>> >>>To: Wrenches; Marco Mangelsdorf >>> >>>Subject: [RE-wrenches] Inverter oversizing >>> >>>Attached is a graph that I produced to document the effect of various >>> ratios >>>between the PV array size and the inverter size. I extracted output >>> power data >>>for a 1020-watt system located in NE Oregon that is on the Sunny Portal >>><http://www.sunnyportal.com/Templates/PublicPageOverview.aspx?page=85820a73-a347-48fb-b8d1-92e5f9b78ab3&plant=608681a7-ef60-4edb-84ff-07110db0ab6a&splang=en-US >>> > . The data are publicly accessible so feel free to run your own >>> analysis. >>>Better yet, analyze the data for a system near you. >>> >>> >>> >>>Using 2009 data, I looked at how much energy would have been lost if the >>> output >>>was clipped at 800W, 810W, .... 1020W. I used 2009 data because there >>> was a >>>period in 2010 when the Sunny Webbox didn't have internet access. At >>> 800 watts, >>>power clipping would have happened on about 25% of the days. Yet the >>> energy >>>that would have been lost was only 0.38% of the annual total. >>> >>> >>> >>>The results shown on this graph aren't universal, results would be a >>> little >>>different in 2010, it would be different in some other climate, it would >>> have >>>been different at another elevation, it would be different with a >>> different >>>array angle, ..., and the module tolerance and inverter efficiency also >>> effect >>>the results. Modules in this system are Suntech 170-watt +/-3%. The >>> inverter >>>is Sunnyboy 1800 that should be operating at close to 93% efficiency. >>> >>> >>>Kent Osterberg >>> >>>Blue Mountain Solar. Inc. >>> >>> >>> >>>_______________________________________________ List sponsored by Home >>> Power >>>magazine List Address: RE-wrenches@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  >>>_______________________________________________ > List sponsored by Home Power magazine > > List Address: RE-wrenches@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 > > > _______________________________________________ > List sponsored by Home Power magazine > > List Address: RE-wrenches@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 > > _______________________________________________ List sponsored by Home Power magazine List Address: RE-wrenches@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
