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<p class="MsoNormal"><span style="font-size:11.0pt">Most modern string inverters have a DC-DC boost phase to allow a wide DC voltage operation. Whatever voltage the inverter side works at is where the inverter will be most efficient, and thus generate less
heat. <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">So it is not really accurate to say high voltage is worse than low voltage for the “heat kills” concern (which I agree with). The same is true for DC-DC optimizers – they contain a boost/buck circuit that
has an optimum efficiency point in the midrange of the DC operating voltage...<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt">Current a bit more complicated but generally efficiency curves for inverters are pretty flat above 10-15% loading. Obviously the same efficiency operation generates more heat when processing more power –
so good thermal design matters. And removing as much power conversion equipment from under the array should help reduce thermal load and cycling too (but that is definitely a biased opinion =) )<o:p></o:p></span></p>
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<p class="MsoNormal">Mike<o:p></o:p></p>
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<b>Michael Mahon</b> (he/him)<b><br>
</b>Solar Academy Manager | SMA America <span style="font-size:11.0pt"><o:p></o:p></span></p>
<p class="MsoNormal">+1 916 918 9412<u><br>
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<p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> RE-wrenches <re-wrenches-bounces@lists.re-wrenches.org>
<b>On Behalf Of </b>Jerry Shafer via RE-wrenches<br>
<b>Sent:</b> Monday, January 27, 2025 10:21 PM<br>
<b>To:</b> RE-wrenches <re-wrenches@lists.re-wrenches.org><br>
<b>Cc:</b> Jerry Shafer <jerrysgarage01@gmail.com><br>
<b>Subject:</b> Re: [RE-wrenches] PV watts question<o:p></o:p></span></p>
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<p class="MsoNormal">Wrenches, <o:p></o:p></p>
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<p class="MsoNormal">So MPPT,s working at high voltage high and high current with even with the electronic switching you will generate heat and over time heat kills<o:p></o:p></p>
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<p class="MsoNormal">Fun times<o:p></o:p></p>
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<p class="MsoNormal">On Mon, Jan 27, 2025, 8:04<span style="font-family:"Arial",sans-serif"> </span>PM Jeff Clearwater via RE-wrenches <<a href="mailto:re-wrenches@lists.re-wrenches.org">re-wrenches@lists.re-wrenches.org</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">Ahh I see the light now on the inverter size point. Still I wonder if all MPPts are made equal in terms if they ability to clip high ratios with no ill-effects. <o:p></o:p></p>
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<p class="MsoNormal">Sent from my iPhone<o:p></o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">On Jan 27, 2025, at 7:55<span style="font-family:"Arial",sans-serif"> </span>PM, Jeff Clearwater <<a href="mailto:jeffc@villagepowerdesign.com" target="_blank">jeffc@villagepowerdesign.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Tahoma",sans-serif"></span>Yes I’ve wondered about this too and there is much debate on forums etc about exactly how this works. <o:p></o:p></p>
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<p class="MsoNormal">Large PV plants have long used 1.4 order of magnitude ratios to maximize economics (but much of that was under “per watt” incentives rather than performance based incentives). <o:p></o:p></p>
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<p class="MsoNormal">However I’ve long wondered what the true effect of red-lining MPPTs is. I’ve seen it as more of a lifetime issue but I wonder that if you consider overheating of the circuit if we might actually be clipping more than just squaring the top
off the curve. Perhaps PVWatts modeled this? They are pretty thorough there at NREL. Or perhaps they have a bug or sloppy programming. It would be worth asking them. Anyone got a buddy at NREL we can ask? <o:p></o:p></p>
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<p class="MsoNormal">Sent from my iPhone<o:p></o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">On Jan 27, 2025, at 12:43<span style="font-family:"Arial",sans-serif"> </span>PM, jay via RE-wrenches <<a href="mailto:re-wrenches@lists.re-wrenches.org" target="_blank">re-wrenches@lists.re-wrenches.org</a>>
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<p class="MsoNormal"><span style="font-family:"Tahoma",sans-serif"></span>HI David,<o:p></o:p></p>
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<p class="MsoNormal">My point exactly. <o:p></o:p></p>
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<p class="MsoNormal">On Jan 27, 2025, at 1:35<span style="font-family:"Arial",sans-serif"> </span>PM, david quattro via RE-wrenches <<a href="mailto:re-wrenches@lists.re-wrenches.org" target="_blank">re-wrenches@lists.re-wrenches.org</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">Jay you are right - that doesn’t make sense because with more PV, the system will reach “max AC out“ power sooner every morning and hold it longer into the evening<o:p></o:p></p>
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<p class="MsoNormal">On Mon, Jan 27, 2025 at 12:20<span style="font-family:"Arial",sans-serif"> </span>PM George McClellan via RE-wrenches <<a href="mailto:re-wrenches@lists.re-wrenches.org" target="_blank">re-wrenches@lists.re-wrenches.org</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">Probably due to clipping. The panels are generating more energy than the power electronics can process, so that excess energy gets cut off (or clipped). It looks like a 1.2 ratio is optimal.<br>
<br>
George McClellan | Senior Manager, Technical Sales | REC Americas LLC<br>
<a href="https://www.google.com/maps/search/735+Tank+Farm+Rd+Ste+130+%7C+San+Luis+Obispo,+CA+%7C93401?entry=gmail&source=g" target="_blank">735 Tank Farm Rd Ste 130 | San Luis Obispo, CA |93401</a><br>
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george.mcclellan@recgroup.com</a><br>
<br>
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<br>
-----Original Message-----<br>
From: RE-wrenches <<a href="mailto:re-wrenches-bounces@lists.re-wrenches.org" target="_blank">re-wrenches-bounces@lists.re-wrenches.org</a>> On Behalf Of jay via RE-wrenches<br>
Sent: Monday, January 27, 2025 11:56 AM<br>
To: RE-wrenches <<a href="mailto:re-wrenches@lists.re-wrenches.org" target="_blank">re-wrenches@lists.re-wrenches.org</a>><br>
Cc: jay <<a href="mailto:jay.peltz@gmail.com" target="_blank">jay.peltz@gmail.com</a>><br>
Subject: [RE-wrenches] PV watts question<br>
<br>
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HI All<br>
<br>
I’m working with a customer who’s pretty savvy and is using PV watts for his design.<br>
<br>
What I can’t figure out is the kwh/year goes down if he uses dc/ac ration of 1.5 instead of 1.2 which is the default.<br>
<br>
Hes in Santa Fe NM.<br>
<br>
.8 ratio= 1663 kwh/yr<br>
1.0 ratio = 1668 kwh/yr<br>
1.2 ratio = 1671 kwh/yr<br>
1.5 ratio = 1623 kwh/yr<br>
<br>
I was expecting that more PV = more kWh/yr.<br>
<br>
What am i missing?<br>
<br>
<br>
standard module<br>
fixed roof mount<br>
14.08 loss’s<br>
10 degree tilt<br>
180 degrees<br>
<br>
<br>
<br>
jay<br>
<br>
<br>
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