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 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=85820a73-a3 > 47-48fb-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. >
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