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<TITLE>Re: [RE-wrenches] Inverter oversizing</TITLE>
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<FONT FACE="Calibri, Verdana, Helvetica, Arial"><SPAN STYLE='font-size:11pt'>Kent, <BR>
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The graphs aren’t 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.<BR>
<BR>
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:<BR>
<BR>
“Considerable differences emerge when looking at the high end of the radiation level<BR>
Distribution, which shows for the one-minute averages that some 9% of the daytime <BR>
hours present radiation levels ≥ 1000W/m2, with a corresponding energy content of<BR>
some 23%; hourly averages for the same range correspond to around 6% of daytime <BR>
hours, and below 11% of the total energy content. Radiation levels above 900W/m2 <BR>
occur some 16% of the time when looking at one-minute averages, and below 13% <BR>
of daytime hours when using hourly averages, with corresponding energy fractions <BR>
respectively above 38% and 25%.”<BR>
<BR>
>From the conclusion:<BR>
<BR>
“we have demonstrated that the estimation of the actual losses due to inverter<BR>
undersizing increases with increased time resolution of the radiation measurements, <BR>
revealing that hourly averages hide important irradiation peaks. In fact, results with <BR>
hourly averages are an experimental artifact, and lead to an estimation of the solar <BR>
energy resource distribution that does not correspond to reality. Hourly averages of<BR>
irradiation values lead to inverter undersizing and the associated energy losses.”<BR>
<BR>
Figures 8 & 9 are interesting. You could imagine what these results would look like if overlaid onto your charts. <BR>
<BR>
Best, david<BR>
<BR>
On 1/19/11 8:14 PM, "Kent Osterberg" <<a href="kent@coveoregon.com">kent@coveoregon.com</a>> wrote:<BR>
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</SPAN></FONT><BLOCKQUOTE><FONT FACE="Calibri, Verdana, Helvetica, Arial"><SPAN STYLE='font-size:11pt'>David,<BR>
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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.<BR>
<BR>
Kent Osterberg<BR>
Blue Mountain Solar, Inc.<BR>
<BR>
<BR>
<BR>
David Brearley wrote: <BR>
</SPAN></FONT><BLOCKQUOTE><FONT FACE="Calibri, Verdana, Helvetica, Arial"><SPAN STYLE='font-size:11pt'> Re: [RE-wrenches] Inverter oversizing This reminds me of a scholarly article I came across about a year ago while doing some research. Here’s a link to it if anyone is interested:<BR>
<BR>
www.lepten.ufsc.br/publicacoes/solar/eventos/2005/PSC/burger_ruther.pdf <<a href="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</a>> <BR>
<BR>
David Brearley, Senior Technical Editor<BR>
<I>SolarPro</I> magazine <BR>
NABCEP Certified PV Installer ™<BR>
<a href="david.brearley@solarprofessional.com">david.brearley@solarprofessional.com</a><BR>
Direct: 541.261.6545<BR>
<BR>
On 1/19/11 12:29 PM, "Bill Brooks" <<a href="billbrooks7@yahoo.com">billbrooks7@yahoo.com</a>> wrote:<BR>
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</SPAN></FONT><BLOCKQUOTE><FONT FACE="Calibri, Verdana, Helvetica, Arial"><SPAN STYLE='font-size:11pt'><FONT COLOR="#1F497D">Kent,<BR>
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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 don’t 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.<BR>
<BR>
This is also a deficiency in modeling software since most models are using hourly data.<BR>
<BR>
Bill.<BR>
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</FONT> </SPAN></FONT><FONT SIZE="2"><FONT FACE="Tahoma, Verdana, Helvetica, Arial"><SPAN STYLE='font-size:10pt'><B>From:</B> <a href="re-wrenches-bounces@lists.re-wrenches.org">re-wrenches-bounces@lists.re-wrenches.org</a> [<a href="mailto:re-wrenches-bounces@lists.re-wrenches.org">mailto:re-wrenches-bounces@lists.re-wrenches.org</a>] <B>On Behalf Of </B>Kent Osterberg<BR>
<B>Sent:</B> Tuesday, January 18, 2011 1:18 PM<BR>
<B>To:</B> Wrenches; Marco Mangelsdorf<BR>
<B>Subject:</B> [RE-wrenches] Inverter oversizing<BR>
</SPAN></FONT></FONT><FONT FACE="Times New Roman"><SPAN STYLE='font-size:12pt'> <BR>
<BR>
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 <<a href="http://www.sunnyportal.com/Templates/PublicPageOverview.aspx?page=85820a73-a347-48fb-b8d1-92e5f9b78ab3&plant=608681a7-ef60-4edb-84ff-07110db0ab6a&splang=en-US">http://www.sunnyportal.com/Templates/PublicPageOverview.aspx?page=85820a73-a347-48fb-b8d1-92e5f9b78ab3&plant=608681a7-ef60-4edb-84ff-07110db0ab6a&splang=en-US</a>> . The data are publicly accessible so feel free to run your own analysis. Better yet, analyze the data for a system near you. <BR>
<BR>
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. <BR>
<BR>
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.<BR>
<BR>
Kent Osterberg<BR>
Blue Mountain Solar. Inc.<BR>
<BR>
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</SPAN></FONT></FONT><FONT FACE="Calibri, Verdana, Helvetica, Arial"><SPAN STYLE='font-size:11pt'>David Brearley, Senior Technical Editor<BR>
<I>SolarPro</I> magazine <BR>
NABCEP Certified PV Installer ™<BR>
<a href="david.brearley@solarprofessional.com">david.brearley@solarprofessional.com</a><BR>
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