<div dir="ltr"><div>Thanks for the info everyone. Bill's Solar Pro article notes that min Vmp on inverters is affected by grid voltage. Is that universally true or just for some inverters? Does that mean that models that work on 240VAC and 208VAC have different min Vmp? I rarely see inverter DC input specs listed differently for different AC voltages. <br>
<br></div>Thanks,<br><div class="gmail_extra"><br clear="all"><div><div dir="ltr">Dana<br><br>Dana Brandt<br>Ecotech Energy Systems, LLC<br><a href="http://www.ecotechenergy.com" target="_blank">www.ecotechenergy.com</a><br>
<a href="mailto:dana@ecotechenergy.com" target="_blank">dana@ecotechenergy.com</a><br>360.318.7646</div></div>
<br><br><div class="gmail_quote">On Wed, Jun 4, 2014 at 3:53 PM, Bill Brooks <span dir="ltr"><<a href="mailto:billbrooks7@yahoo.com" target="_blank">billbrooks7@yahoo.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="white" link="blue" vlink="purple" lang="EN-US"><div><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Folks,<u></u><u></u></span></p><p class="MsoNormal">
<span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Voc does not degrade as much as Isc, but neither is key.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Both Vmp and Imp degrade. We call this a degradation of Fill Factor. This happens with all PV systems and the degradation rates for current and voltage are very similar.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Imp and Isc degrade because less light gets to the cell from etching glass, yellowing encapsulant and IR coating on cells changing.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Vmp changes because of increased contact resistance of conductors on the cells and other contact points. Voc is unimpacted by contact resistance since there is no current flow.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Bill.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><u></u> <u></u></span></p><div><div style="border:none;border-top:solid #e1e1e1 1.0pt;padding:3.0pt 0in 0in 0in">
<p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:windowtext">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:windowtext"> RE-wrenches [mailto:<a href="mailto:re-wrenches-bounces@lists.re-wrenches.org" target="_blank">re-wrenches-bounces@lists.re-wrenches.org</a>] <b>On Behalf Of </b>Ray Walters<br>
<b>Sent:</b> Wednesday, June 04, 2014 11:30 AM</span></p><div class=""><br><b>To:</b> RE-wrenches<br><b>Subject:</b> Re: [RE-wrenches] Module Degradation - voltage or current?<u></u><u></u></div><p></p></div></div><p class="MsoNormal">
<u></u> <u></u></p><div><p class="MsoNormal">I agree that Voc doesn't seem to degrade as much. I've had a chance to measure several modules over 20 years old, and the Voc is only dropping about 1/2 the rate suggested by others here. I think a more appropriate number might be 0.25% V drop/ year. <br>
<br><u></u><u></u></p><div><div class="h5"><pre>R.Ray Walters<u></u><u></u></pre><pre>CTO, Solarray, Inc<u></u><u></u></pre><pre>Nabcep Certified PV Installer, <u></u><u></u></pre><pre>Licensed Master Electrician<u></u><u></u></pre>
<pre>Solar Design Engineer<u></u><u></u></pre><pre><a href="tel:303%20505-8760" value="+13035058760" target="_blank">303 505-8760</a><u></u><u></u></pre><p class="MsoNormal">On 6/4/2014 11:36 AM, Nathan Charles wrote:<u></u><u></u></p>
</div></div></div><div><div class="h5"><blockquote style="margin-top:5.0pt;margin-bottom:5.0pt"><div><p class="MsoNormal">So I read this paper, Smith, R. M., Jordan, D. C., & Kurtz, S. R. (2012). Outdoor PV Module Degradation of Current-Voltage Parameters, which seems to seems to suggest that Voc doesn't degrade like Isc degrades. Based on that and other data I've seen it seems like panels that degrade at 0.5%/year are outliers on the low side. <u></u><u></u></p>
<div><p class="MsoNormal"><u></u> <u></u></p></div><div><p class="MsoNormal">Thoughts from other wrenches?<u></u><u></u></p></div><div><p class="MsoNormal"><u></u> <u></u></p></div><div><p class="MsoNormal"><u></u> <u></u></p>
</div></div><div><p class="MsoNormal" style="margin-bottom:12.0pt"><u></u> <u></u></p><div><p class="MsoNormal">On Tue, Jun 3, 2014 at 11:59 PM, Bill Hoffer <<a href="mailto:sunengser@gmail.com" target="_blank">sunengser@gmail.com</a>> wrote:<u></u><u></u></p>
<blockquote style="border:none;border-left:solid #cccccc 1.0pt;padding:0in 0in 0in 6.0pt;margin-left:4.8pt;margin-right:0in"><div><p class="MsoNormal">Dana <u></u><u></u></p><div><p class="MsoNormal"><u></u> <u></u></p></div>
<div><p class="MsoNormal">Bill Brooks, passed on past data, ( correct me Bill if I am out of date here) recommends 1% Power loss per year with approximately 0.5% current and 0.5%voltage. That is also what Solar Energy International Best Practices curriculum recommends. Based on some newer data from larger projects requiring testing to actually determine those values for the Bankability requirements ( PVsyst PAN files), I believe we are seeing lower numbers than that now. In general, quality of modules are higher than the older modules. We of course are usually not privy to those results and may not even be getting the same level of binning for small residential projects as the MW projects do. 0.5% V loss per year seems like a like a good conservative number to me, especially if you add a little buffer (1-2%) in there.<u></u><u></u></p>
</div><div><p class="MsoNormal"><u></u> <u></u></p></div><div><p class="MsoNormal">Bill<u></u><u></u></p></div></div><div><p class="MsoNormal" style="margin-bottom:12.0pt"><u></u> <u></u></p><div><p class="MsoNormal">On Tue, Jun 3, 2014 at 3:41 PM, Dana Brandt <<a href="mailto:dana@ecotechenergy.com" target="_blank">dana@ecotechenergy.com</a>> wrote:<u></u><u></u></p>
<blockquote style="border:none;border-left:solid #cccccc 1.0pt;padding:0in 0in 0in 6.0pt;margin-left:4.8pt;margin-right:0in"><div><p class="MsoNormal">Hi Wrenches,<br><br>Does anyone know what percentage of module degradation over time is voltage and what is current? I'm wanting to make sure we give ourselves plenty of breathing room on the minimum Vmp of the inverters over the long term so need to try to anticipate how much voltage we'll lose on the array over 30 years. <br>
<br>Thanks,<br><br clear="all"><u></u><u></u></p><div><div><div><div><p class="MsoNormal">Dana<span style="color:#888888"><br><br>Dana Brandt<br>Ecotech Energy Systems, LLC<br><a href="http://www.ecotechenergy.com" target="_blank">www.ecotechenergy.com</a><br>
<a href="mailto:dana@ecotechenergy.com" target="_blank">dana@ecotechenergy.com</a><br><a href="tel:360.318.7646" target="_blank">360.318.7646</a></span><u></u><u></u></p></div></div></div></div></div><p class="MsoNormal" style="margin-bottom:12.0pt">
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