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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'>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>
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www.lepten.ufsc.br/publicacoes/solar/eventos/2005/PSC/burger_ruther.pdf<BR>
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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>
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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>
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This is also a deficiency in modeling software since most models are using hourly data.<BR>
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Bill.<BR>
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</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>
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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>
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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>
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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>
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Kent Osterberg<BR>
Blue Mountain Solar. Inc.<BR>
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