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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><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"><span style='color:blue'>www.vermontsolarnow.com</span></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>