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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal>I’ll give a different spin and of course each situation is different and to be judged on its own facts. Here in Texas, modules on a summer day don’t typically perform to STC ratings and a DC/AC over-ratio is entirely appropriate. I’ve brought it up to 1.25 in some cases.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I look at the economics differently: you’re putting in the same 10KW inverters, the same 10KW appropriate wires and conduit, the same OCPD, the same BOS costs for paperwork…so why not use all of that capacity a bit more. Instead of looking at the lost DC clipping, think about the increased use of inverter and beyond components.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>With a very modest cost increase, you’re using that side of the system more (at same cost as it would be for a 10KW DC to 10KW AC system).<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Yes, in the spring, I might see some midday clipping but a small price to pay for increase year round performance. Your Vermont conditions might not play out like my Texas conditions since you live closer to STC than I do.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><b>Howard “Scot” Arey<o:p></o:p></b></p><p class=MsoNormal>254-300-1228<o:p></o:p></p><p class=MsoNormal><a href="mailto:scot.arey@solarcentex.com"><span style='color:#0563C1'>scot.arey@solarcentex.com</span></a><o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><img border=0 width=167 height=167 style='width:1.7343in;height:1.7343in' id="Picture_x0020_1" src="cid:image001.png@01D1DD18.A9B1A400" alt="Solar Centex Logo - No Back.png 10 percent resize"><o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><a name="_MailEndCompose"><o:p> </o:p></a></p><span style='mso-bookmark:_MailEndCompose'></span><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal><b>From:</b> RE-wrenches [mailto:re-wrenches-bounces@lists.re-wrenches.org] <b>On Behalf Of </b>Kirk Herander<br><b>Sent:</b> Wednesday, July 13, 2016 2:02 PM<br><b>To:</b> RE-wrenches <re-wrenches@lists.re-wrenches.org><br><b>Subject:</b> [RE-wrenches] array overloading of an inverter<o:p></o:p></p></div></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><span style='font-size:18.0pt'>Hello folks,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:18.0pt'>I am composing a response to a question a potential customer asked me. It seems a competitor is trying to talk him into a 20% larger KW array than the inverter AC max output rating is. The idea of course is to generate more power on either side of peak output, but at a cost I don’t feel is justified. My opinion of this particular big-box installer I will keep to myself. My response to the customer, trying to keep it simple:<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:18.0pt'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:18.0pt'>“On the DC array input side, most inverters do allow an overload factor. For instance, a 10kw AC inverter may allow for 12 kw of DC array as an input. Whether or not this is a good idea boils down to economics and technical reasons.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:18.0pt'>On a sunny day, the inverter generates power as a typical bell curve. Power output rises in the morning, peaks at noon, declines in the afternoon. In my example, the inverter can’t output more than 10 kw AC. What overloading the input will do will widen the bell curve, i.e. generating more power in the morning and afternoon, BUT clipping the peak at 10kw on either side of noon. So there is power to be gained in morning and afternoon, but peak power is lost(if conditions allow the peak output to be reached), since the 12 kw array can never be converted to more than 10 kw of AC power. Depending upon time of year(ambient / cell temperature) and weather conditions, the peak may be clipped at 10 kw for several hours a day. So you are both gaining and losing power using this method. And typically the inverters are only overloaded in this manner on large-scale farms where the economics are favorable.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:18.0pt'>In your case, if you could actually put 200kw of DC array into 150 Kw of inverter, the economics would never justify it. That extra 50 kw of array would cost you $100k of more, and the dollar payback for the power that extra 50Kw would generate will take 2 – 3x the time that the array size does that stays inside the output limit of the inverters. This is why I’m not a big fan of dramatically overloading the inverters, if at all, in your case. <b>Any KW portion of the array which is above the nameplate kw rating of the inverter is going to have a longer payback for these reasons. “<o:p></o:p></b></span></p><p class=MsoNormal><span style='font-size:18.0pt'>I feel my reasoning is sound, But I don’t want to be too loose with the facts. Comments are appreciated. Thanks.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:18.0pt'><o:p> </o:p></span></p><p class=MsoNormal><b><span style='font-size:16.0pt'>Kirk Herander<o:p></o:p></span></b></p><p class=MsoNormal><b><span style='font-size:16.0pt'>Owner|Principal, VT Solar, LLC <o:p></o:p></span></b></p><p class=MsoNormal><b><i><span style='font-size:16.0pt'>Celebrating our 25<sup>th</sup> Anniversary 1991-2016<o:p></o:p></span></i></b></p><p class=MsoNormal><b><span style='font-size:16.0pt'><a href="www.vermontsolarnow.com">www.vermontsolarnow.com</a><o:p></o:p></span></b></p><p class=MsoNormal><span style='font-size:16.0pt'>dba Vermont Solar Engineering<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:16.0pt'>NABCEP<sup>TM </sup>2003 Inaugural Certificant<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:16.0pt'>VT RE Incentive Program Partner<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:16.0pt'>802.863.1202</span><span style='font-size:14.0pt'><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:18.0pt'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:18.0pt'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:18.0pt'><o:p> </o:p></span></p></div></body></html>