I see what your looking at; I was comparing Figures 3 & 4, not 2 & 3.
On 1/20/11 2:21 PM, "Kent Osterberg" <[email protected]> wrote: > David, > > Take a close look at the upper and lowers portions of the graphs of the > 10-second data and the 1-minute data for Freiburg. > > To make it easier to see, attached is reproduction of their graphs on one > page. Just as fleeting peaks in irradiance (edge of cloud effect) should be > fewer in the 1 minute averages than in the 10 second raw data; fleeting lows > (caused by passing clouds) should be fewer in the 1 minute averages than in > the 10-second data. Inspect the graph and label which you think is 10-second > data and which you think is 1-minute data. Then compare to the original. The > two graphs appear to be mislabeled. > > Kent Osterberg > Blue Mountain Solar, Inc. > > > > David Brearley wrote: >> Re: [RE-wrenches] Inverter oversizing Kent, >> >> The graphs aren¹t mislabeled. The one-minute average data has more >> granularity, which shows up at the upper limits of the data. It reveals more >> peaks over 1,000 W/m2, even in excess of 1,200 W/m2. These values get >> compressed into the lower bins in the hourly data. >> >> The results from the Florianopolis site in Brazil, gives a pretty good idea >> of how significantly different the results can be based on monitoring >> frequency: >> >> ³Considerable differences emerge when looking at the high end of the >> radiation level >> Distribution, which shows for the one-minute averages that some 9% of the >> daytime >> hours present radiation levels 1000W/m2, with a corresponding energy >> content of >> some 23%; hourly averages for the same range correspond to around 6% of >> daytime >> hours, and below 11% of the total energy content. Radiation levels above >> 900W/m2 >> occur some 16% of the time when looking at one-minute averages, and below 13% >> of daytime hours when using hourly averages, with corresponding energy >> fractions >> respectively above 38% and 25%.² >> >>> >From the conclusion: >> >> ³we have demonstrated that the estimation of the actual losses due to >> inverter >> undersizing increases with increased time resolution of the radiation >> measurements, >> revealing that hourly averages hide important irradiation peaks. In fact, >> results with >> hourly averages are an experimental artifact, and lead to an estimation of >> the solar >> energy resource distribution that does not correspond to reality. Hourly >> averages of >> irradiation values lead to inverter undersizing and the associated energy >> losses.² >> >> Figures 8 & 9 are interesting. You could imagine what these results would >> look like if overlaid onto your charts. >> >> Best, david >> >> On 1/19/11 8:14 PM, "Kent Osterberg" <[email protected]> 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: >>> >>>> Re: [RE-wrenches] Inverter oversizing This reminds me of a scholarly >>>> article I came across about a year ago while doing some research. Here¹s a >>>> link to it if anyone is interested: >>>> >>>> www.lepten.ufsc.br/publicacoes/solar/eventos/2005/PSC/burger_ruther.pdf >>>> <http://www.lepten.ufsc.br/publicacoes/solar/eventos/2005/PSC/burger_ruther >>>> .pdf> >>>> <http://www.lepten.ufsc.br/publicacoes/solar/eventos/2005/PSC/burger_ruther >>>> .pdf> >>>> >>>> David Brearley, Senior Technical Editor >>>> SolarPro magazine >>>> NABCEP Certified PV Installer >>>> [email protected] >>>> Direct: 541.261.6545 >>>> >>>> On 1/19/11 12:29 PM, "Bill Brooks" <[email protected]> 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 don¹t 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: [email protected] >>>>> [mailto:[email protected]] 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=85820a7 >>>>> 3-a347-48fb-b8d1-92e5f9b78ab3&plant=608681a7-ef60-4edb-84ff-07110db0ab6a&s >>>>> plang=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: [email protected] >>>> >>>> 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 >>>> <http://www.re-wrenches.org/etiquette.htm> >>>> <http://www.re-wrenches.org/etiquette.htm> >>>> >>>> Check out participant bios: >>>> www.members.re-wrenches.org <http://www.members.re-wrenches.org> >>>> <http://www.members.re-wrenches.org> >>>> >>>> >>>> >>> >>> >>> >>> _______________________________________________ >>> List sponsored by Home Power magazine >>> >>> List Address: [email protected] >>> >>> 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 <http://www.re-wrenches.org/etiquette.htm> >>> >>> Check out participant bios: >>> www.members.re-wrenches.org <http://www.members.re-wrenches.org> >>> >>> >> >> David Brearley, Senior Technical Editor >> SolarPro magazine >> NABCEP Certified PV Installer >> [email protected] >> Direct: 541.261.6545 >> Fax: 541.512.0343 >> >> Visit our Web site at solarprofessional.com >> >> (Sample copy available for download at: solarprofessional.com/sample) >> >> >> >> >> >> >> _______________________________________________ >> List sponsored by Home Power magazine >> >> List Address: [email protected] >> >> 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 <http://www.re-wrenches.org/etiquette.htm> >> >> Check out participant bios: >> www.members.re-wrenches.org <http://www.members.re-wrenches.org> >> >> > > > _______________________________________________ > List sponsored by Home Power magazine > > List Address: [email protected] > > 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 > David Brearley, Senior Technical Editor SolarPro magazine NABCEP Certified PV Installer [email protected] Direct: 541.261.6545 Fax: 541.512.0343 Visit our Web site at solarprofessional.com (Sample copy available for download at: solarprofessional.com/sample)
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