<html><head><style type="text/css"><!-- DIV {margin:0px;} --></style></head><body><div style="font-family:arial, helvetica, sans-serif;font-size:10pt"><div>It makes sense to never drive your car at top speed for the tires, engine etc. and this generally applies to virtually any type of technology we own.</div><div><br></div><div>There can be an argument made to say the engineers have put in a safety factor, so don't worry, but I'd like my inverter to have a longer service life.</div><div><br></div><div>When you factor in heat on components and the cycling they experience, plus the added edge of cloud effects, it seems prudent to lean on the side of being conservative.</div><div><br></div><div>Seems like if we don't we will be replacing lots of inverters in the coming years. We really don't know how mods will perform over time. The whole + - what their nameplate is, is anyones guess.</div><div><br></div><div>Out here in the tropics, we already need to
contend with humidity and salt with the heat, so being mindful of the variables is important.</div><div><br></div><div>However, many integrators in a sales type of environment could encourage putting more mods on an inverter to sell more horsepower.</div><div><br></div><div>Keith</div><div style="font-family:arial, helvetica, sans-serif;font-size:10pt"><br><div style="font-family:times new roman, new york, times, serif;font-size:12pt"><font size="2" face="Tahoma"><hr size="1"><b><span style="font-weight: bold;">From:</span></b> Dave Palumbo <dave@independentpowerllc.com><br><b><span style="font-weight: bold;">To:</span></b> RE-wrenches <re-wrenches@lists.re-wrenches.org><br><b><span style="font-weight: bold;">Sent:</span></b> Wed, January 19, 2011 1:55:19 PM<br><b><span style="font-weight: bold;">Subject:</span></b> Re: [RE-wrenches] Inverter oversizing<br></font><br>
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--></style><div class="WordSection1"><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"sans-serif";color:#1F497D;">Bill,</span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"sans-serif";color:#1F497D;"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"sans-serif";color:#1F497D;">In addition to power production losses due to arrays that are oversized for the inverter (although within manufacturers specs) how concerned should we be with shorter inverter service life because the inverter is working at its maximum?</span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"sans-serif";color:#1F497D;"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"sans-serif";color:#1F497D;">David Palumbo</span></p><p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"sans-serif";color:#1F497D;">Independent Power LLC </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"sans-serif";color:#1F497D;">462 Solar Way Drive</span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"sans-serif";color:#1F497D;">Hyde Park, VT 05655<b></b></span></p><p class="MsoNormal"><b><i><span style="font-size:11.0pt;font-family:"sans-serif";color:#1F497D;"><a target="_blank" href="http://www.independentpowerllc.com">www.independentpowerllc.com</a> </span></i></b></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"sans-serif";color:#1F497D;">NABCEP Certified PV Installer</span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"sans-serif";color:#1F497D;">Vermont Solar Partner</span></p><p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"sans-serif";color:#1F497D;">23 Years Experience, (802) 888-7194 </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"sans-serif";color:#1F497D;"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"sans-serif";color:#1F497D;"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"sans-serif";color:#1F497D;"> </span></p><div><div style="border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in;"><p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"sans-serif";color:windowtext;">From:</span></b><span style="font-size:10.0pt;font-family:"sans-serif";color:windowtext;"> re-wrenches-bounces@lists.re-wrenches.org [mailto:re-wrenches-bounces@lists.re-wrenches.org] <b>On Behalf Of </b>Bill Brooks<br><b>Sent:</b> Wednesday, January 19, 2011 6:20
PM<br><b>To:</b> 'RE-wrenches'<br><b>Subject:</b> Re: [RE-wrenches] Inverter oversizing</span></p></div></div><p class="MsoNormal"> </p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"sans-serif";color:#1F497D;">Kent,</span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"sans-serif";color:#1F497D;"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"sans-serif";color:#1F497D;">The article that David Brearley cited is a very good discussion on this subject. It clearly shows the under-prediction of losses due to hitting the inverter peak power capability when using longer-term data. This study was done by the Fraunhofer Institute in southern Germany. They get a lot more clouds there so the results might be comparable to some of the more cloudy regions of the United States. I would expect the results to be worse in much of the U.S. that gets clouds and
higher irradiation than Freiburg. However, the results will definitely be less for much of California since clouds don’t happen for sections of the year. </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"sans-serif";color:#1F497D;"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"sans-serif";color:#1F497D;">It all matters where you are.</span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"sans-serif";color:#1F497D;"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"sans-serif";color:#1F497D;">Great discussion.</span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"sans-serif";color:#1F497D;"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"sans-serif";color:#1F497D;">Bill.</span></p><p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"sans-serif";color:#1F497D;"> </span></p><div><div style="border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in;"><p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"sans-serif";color:windowtext;">From:</span></b><span style="font-size:10.0pt;font-family:"sans-serif";color:windowtext;"> re-wrenches-bounces@lists.re-wrenches.org [mailto:re-wrenches-bounces@lists.re-wrenches.org] <b>On Behalf Of </b>Kent Osterberg<br><b>Sent:</b> Wednesday, January 19, 2011 1:41 PM<br><b>To:</b> RE-wrenches<br><b>Subject:</b> Re: [RE-wrenches] Inverter oversizing</span></p></div></div><p class="MsoNormal"> </p><p class="MsoNormal">Bill,<br><br>The data are 15 minute averages so I'm sure that some edge of cloud events are washed out in the average. The energy they contributed was in the total measurement, but wouldn't have been included in my sum of clipped
output. Observing the data, you can see some edge of cloud effects despite the 15 minute averaging. And on many days I suspect there is edge of cloud effect that wouldn't have hit the clipping limit too. Obviously, missing some short interval events biases the results a little but probably not by very much. For the sake of argument assume that there was a 3 minute, spike in output 100-watts above my threshold setting. In the 15-minute average that still would have been a 20-watt bump and with 10-watt data resolution, it probably would have showed up, but say it didn't show up or that it end up just below the threshold. Say this happened once every week, not likely, but if it did the missed data would amount to 0.25 kWhr or about 5% as much as the total observed with the data clipped at 800 watts. So you have to really stretch the brief edge of cloud argument to integrate enough energy to throw my graph off by
very much.<br><br>Kent Osterberg<br>Blue Mountain Solar, Inc.<br><br><br><br>Bill Brooks wrote: </p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"sans-serif";color:#1F497D;">Kent,</span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"sans-serif";color:#1F497D;"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"sans-serif";color:#1F497D;">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.</span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"sans-serif";color:#1F497D;"> </span></p><p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"sans-serif";color:#1F497D;">This is also a deficiency in modeling software since most models are using hourly data.</span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"sans-serif";color:#1F497D;"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"sans-serif";color:#1F497D;">Bill.</span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"sans-serif";color:#1F497D;"> </span></p><div><div style="border:none;border-top:solid windowtext 1.0pt;padding:3.0pt 0in 0in 0in;"><p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"sans-serif";color:windowtext;">From:</span></b><span style="font-size:10.0pt;font-family:"sans-serif";color:windowtext;"> <a rel="nofollow" ymailto="mailto:re-wrenches-bounces@lists.re-wrenches.org" target="_blank"
href="mailto:re-wrenches-bounces@lists.re-wrenches.org">re-wrenches-bounces@lists.re-wrenches.org</a> [<a rel="nofollow" ymailto="mailto:re-wrenches-bounces@lists.re-wrenches.org" target="_blank" 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</span></p></div></div><p class="MsoNormal"> </p><p class="MsoNormal" style="margin-bottom:12.0pt;"><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 <a rel="nofollow" target="_blank"
href="http://www.sunnyportal.com/Templates/PublicPageOverview.aspx?page=85820a73-a347-48fb-b8d1-92e5f9b78ab3&plant=608681a7-ef60-4edb-84ff-07110db0ab6a&splang=en-US">Sunny Portal</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></p><pre> </pre><pre style="text-align:center;"><hr size="4" width="90%" align="center"></pre><pre> </pre><pre>_______________________________________________</pre><pre>List sponsored by Home Power magazine</pre><pre> </pre><pre>List Address: <a rel="nofollow" ymailto="mailto:RE-wrenches@lists.re-wrenches.org" target="_blank" href="mailto:RE-wrenches@lists.re-wrenches.org">RE-wrenches@lists.re-wrenches.org</a></pre><pre> </pre><pre>Options & settings:</pre><pre><span><a target="_blank"
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