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 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. 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- a347-48fb-b8d1-92e5f9b78ab3&plant=608681a7-ef60-4edb-84ff-07110db0ab6a&splan g=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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