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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='color:#1F497D'>Marco,<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>All 3-phase services, and single split-phase services has imbalances from time to time. The question of whether the imbalance is problematic depends on the size of the imbalance relative to the service transformer. Since 3-phase services are generally larger, a 10kW phase-to-phase connected single-phase inverter in unlikely to cause an imbalance problem unless it is indiscriminately placed on the service on the most lightly loaded phases.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>If the above inverter is placed on the two most heavily loaded phases (since it is a negative load), it will often reduce imbalance rather than increase imbalance. A load recorder placed on the service before construction can gather data so that when it comes time to choose the most heavily loaded phases, there is plenty of data to make that decision.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>The inverter in question has the same imbalance impact as a 10kW single-phase water heater on a 3-phase service. If the service utility requires a load analysis to add a water heater, then doing the same for PV is justified. If they don’t require it, they should not require the analysis of the PV inverter.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Bill.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></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:"Tahoma","sans-serif"'>From:</span></b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> re-wrenches-bounces@lists.re-wrenches.org [mailto:re-wrenches-bounces@lists.re-wrenches.org] <b>On Behalf Of </b>Marco Mangelsdorf<br><b>Sent:</b> Friday, December 10, 2010 11:01 AM<br><b>To:</b> 'RE-wrenches'<br><b>Subject:</b> [RE-wrenches] feed-in imbalance<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Now that SMA has come up with their new 8, 9 and 10 kW transformerless line of single-phase 120/208V inverters, it brings up the question once again about how practical and wise it is to have one or two of these inverters feed into a three-phase service. That is, is such an unbalanced feed much, if any, of a big deal?<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I spoke to my consulting E.E. about this and he said that the large majority of utility-provided transformers are so large these days that an unbalanced feed of, say, a 10 kW inverter that only has output power through L1 and L2 should not present a problem.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Any other thoughts out there on this matter?<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Thanks,<o:p></o:p></p><p class=MsoNormal>marco <o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p></div></body></html>