<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40"><head><META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=us-ascii"><meta name=Generator content="Microsoft Word 14 (filtered medium)"><!--[if !mso]><style>v\:* {behavior:url(#default#VML);}
o\:* {behavior:url(#default#VML);}
w\:* {behavior:url(#default#VML);}
.shape {behavior:url(#default#VML);}
</style><![endif]--><style><!--
/* Font Definitions */
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
@font-face
{font-family:Tahoma;
panose-1:2 11 6 4 3 5 4 4 2 4;}
@font-face
{font-family:Consolas;
panose-1:2 11 6 9 2 2 4 3 2 4;}
@font-face
{font-family:Webdings;
panose-1:5 3 1 2 1 5 9 6 7 3;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0in;
margin-bottom:.0001pt;
font-size:11.0pt;
font-family:"Calibri","sans-serif";
color:black;}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:blue;
text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{mso-style-priority:99;
color:purple;
text-decoration:underline;}
pre
{mso-style-priority:99;
mso-style-link:"HTML Preformatted Char";
margin:0in;
margin-bottom:.0001pt;
font-size:10.0pt;
font-family:"Courier New";
color:black;}
p.MsoAcetate, li.MsoAcetate, div.MsoAcetate
{mso-style-priority:99;
mso-style-link:"Balloon Text Char";
margin:0in;
margin-bottom:.0001pt;
font-size:8.0pt;
font-family:"Tahoma","sans-serif";
color:black;}
span.HTMLPreformattedChar
{mso-style-name:"HTML Preformatted Char";
mso-style-priority:99;
mso-style-link:"HTML Preformatted";
font-family:Consolas;
color:black;}
span.EmailStyle19
{mso-style-type:personal;
font-family:"Calibri","sans-serif";
color:windowtext;}
span.EmailStyle20
{mso-style-type:personal;
font-family:"Calibri","sans-serif";
color:#1F497D;}
span.BalloonTextChar
{mso-style-name:"Balloon Text Char";
mso-style-priority:99;
mso-style-link:"Balloon Text";
font-family:"Tahoma","sans-serif";
color:black;}
span.EmailStyle23
{mso-style-type:personal-reply;
font-family:"Calibri","sans-serif";
color:#1F497D;}
.MsoChpDefault
{mso-style-type:export-only;
font-size:10.0pt;}
@page WordSection1
{size:8.5in 11.0in;
margin:1.0in 1.0in 1.0in 1.0in;}
div.WordSection1
{page:WordSection1;}
--></style><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-size:14.0pt;color:#1F497D'>Thanks everyone, John, from your SMA days, can you predict if the 6000US will get stuck on a local MPP?<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:14.0pt;color:#1F497D'><o:p> </o:p></span></p><div><p class=MsoNormal><span style='font-size:14.0pt;color:#1F497D'>Kirk Herander<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:14.0pt;color:#1F497D'>VT Solar, LLC<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:14.0pt;color:#1F497D'>dba Vermont Solar Engineering<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:14.0pt;color:#1F497D'>NABCEP<sup>TM </sup>Certified Inaugural Certificant<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:14.0pt;color:#1F497D'>NYSERDA-eligible Installer<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:14.0pt;color:#1F497D'>VT RE Incentive Program Partner<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:14.0pt;color:#1F497D'>802.863.1202<o:p></o:p></span></p></div><p class=MsoNormal><span style='font-size:14.0pt;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";color:windowtext'>From:</span></b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext'> re-wrenches-bounces@lists.re-wrenches.org [mailto:re-wrenches-bounces@lists.re-wrenches.org] <b>On Behalf Of </b>John Berdner<br><b>Sent:</b> Monday, April 29, 2013 3:12 PM<br><b>To:</b> RE-wrenches<br><b>Subject:</b> Re: [RE-wrenches] unbalanced string voltages<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><div><p class=MsoNormal><span style='color:#1F497D'>Kirk:<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'>As noted below the current will be shared by all modules in the string and the voltage will be the sum of the operating voltage at that current.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>When mixed modules are used this results in differences between the operating voltages of each string in the system.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Having parallel strings with differing max power points will have an effect on the operation of the MPP tracker.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>You should also consider the effect of the mixed modules on the MPPT of the inverter (or charge controller) and resultant reductions in energy yield.<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'>Some inverters can “get stuck” on one of the a local MPP voltage as opposed to global MPP<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>This will reduce the overall energy yield – sometimes significantly.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>A good max power point tracker will find the correct global MPP voltage.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>The global MPP will be at a point that is between the upper and lower operating voltages of all the parallel strings and proportional to the current of each string.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Using your example Strings 1, 2 and 4 are close in voltage.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>For simplicity I will consider them to be the same, i.e. approximately 389 Vdc with 2 strings at 3.6 Amps and 1 string at 5.5 Amps = 12.7 Amps<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>String 3 will be about 378 volts and 3.6 Amps.(the lower of the two module currents)<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Note: You can calculate this voltage of string 3 more closely by looking at the IV curve of the higher current module when running at the lower current, i.e. this module will operate closer to Voc so the MPP voltage of this string will be slightly higher.<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'>Using the numbers from your email, the voltage difference is 11 Vdc and the ratio of the currents is 0.779 = 12.7/(12.7+3.6) so the global MPP voltage should be about 8.6 volts (= 11*0.779) above that of string 3.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>I would therefore expect global maxima to be around 386-387 Vdc (378 + 8.6 V) above the voltage of string 3.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Using 387 Vdc as an operating point you can estimate the mismatch power loss from the IV curves of the various modules.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>String 3 will be operating above it’s MPPT so the modules will be closer to Voc and the current will be reduced further and the overall power of that string will be lower.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Since the current changes as the modules move towards Voc you will need to iterate the calculation a couple of times to get close to the actual operating point and estimated reductions in energy yield.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><div><p class=MsoNormal><span style='color:#1F497D'>Best Regards,<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'>John Berdner<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>General Manager, North America<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'>SolarEdge Technologies, Inc.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>3347 Gateway Boulevard, Fremont CA 94538 USA </span><b><i><span style='color:#C00000'>(*Please note of our new address.)</span></i></b><span style='color:#1F497D'><br>T: 510.498.3200, X 747<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>M: 530.277.4894 <o:p></o:p></span></p></div><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";color:windowtext'>From:</span></b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext'> <a href="mailto:re-wrenches-bounces@lists.re-wrenches.org">re-wrenches-bounces@lists.re-wrenches.org</a> <a href="mailto:[mailto:re-wrenches-bounces@lists.re-wrenches.org]">[mailto:re-wrenches-bounces@lists.re-wrenches.org]</a> <b>On Behalf Of </b>Ray Walters<br><b>Sent:</b> Monday, April 29, 2013 10:41 AM<br><b>To:</b> RE-wrenches<br><b>Subject:</b> Re: [RE-wrenches] unbalanced string voltages<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><div><p class=MsoNormal style='margin-bottom:12.0pt'>Modules aren't exactly constant current devices. <img border=0 width=416 height=302 id="_x0000_i1025" src="cid:image001.gif@01CE457A.A4FCF150" alt="I-V curve"><br>They are for much of their voltage range, up to a voltage a bit below the MPP, and then the current starts tapering down to 0 at Voc. The entire string can only pass as much current as the lowest current module. That means the higher current module will be forced to operate where it can, which is at a higher voltage than its MPP point, as David said. <br>If you don't believe us, hook up a couple of mismatched modules and measure voltage across each module, and the current. Current is always equal in a series connection, then the modules make up for it by moving up or down along their IV curve.<br><br><o:p></o:p></p><pre>R.Ray Walters<o:p></o:p></pre><pre>CTO, Solarray, Inc<o:p></o:p></pre><pre>Nabcep Certified PV Installer, <o:p></o:p></pre><pre>Licensed Master Electrician<o:p></o:p></pre><pre>Solar Design Engineer<o:p></o:p></pre><pre>303 505-8760<o:p></o:p></pre><p class=MsoNormal>On 4/29/2013 9:44 AM, Larry Crutcher, Starlight Solar Power Systems wrote:<o:p></o:p></p></div><blockquote style='margin-top:5.0pt;margin-bottom:5.0pt'><p class=MsoNormal>David, <o:p></o:p></p><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>Since a PV module is a constant current device, I don't believe this will take place. For a given amount of light (plus all factors affecting power), the current potential will be there. What force can act upon the current to reduce it? Consequently, the lowest Vmp the inverter can track will dictate the voltage for all strings. This means less power from the highest Vmp modules. Do you agree? <o:p></o:p></p><div><p class=MsoNormal><br>Larry Crutcher<o:p></o:p></p><div><p class=MsoNormal style='margin-bottom:12.0pt'><br><br><br><o:p></o:p></p></div></div><p class=MsoNormal><o:p> </o:p></p><div><div><p class=MsoNormal>On Apr 28, 2013, at 9:33 AM, David Katz <<a href="mailto:dkatz@aeesolar.com">dkatz@aeesolar.com</a>> wrote:<o:p></o:p></p></div><p class=MsoNormal><o:p> </o:p></p><div><div><p class=MsoNormal>Kirk<o:p></o:p></p></div><div><p class=MsoNormal>The 43volt 5.5 amp panel will operate at 3.6 amps, so it's voltage will move up toward open circuit voltage, raising the mppt voltage of that string. I would bet that the voltage of that entire string will rise to match the higher voltage string by moving toward open circuit voltage. It should work fine.<o:p></o:p></p></div><div><p class=MsoNormal>David Katz<br><br>Sent from my iPhone<o:p></o:p></p></div><div><p class=MsoNormal style='margin-bottom:12.0pt'><br>On Apr 28, 2013, at 9:01 AM, "Kirk Herander" <<a href="mailto:kirk@vtsolar.com">kirk@vtsolar.com</a>> wrote:<o:p></o:p></p></div><blockquote style='margin-top:5.0pt;margin-bottom:5.0pt'><p class=MsoNormal><span style='font-size:14.0pt'>Hello everyone,</span><o:p></o:p></p><p class=MsoNormal><span style='font-size:14.0pt'> </span><o:p></o:p></p><p class=MsoNormal><span style='font-size:14.0pt'>I am at present adding to a -20- panel array of old Sanyo HIT “lipped” 200 watt panels. They are configured in -4- series strings of -5- panels, with a string MPP voltage of 279 vdc (55.8 v, 3.6 a each). The customer wants to add another nominal 2 kw using the (now) Panasonic 235 watt HIT’s which have an MPP of 43.0 vdc, 5.5 a. I am locked in to an existing SMA 6000US inverter. Obviously I cannot get all the strings to the same voltage. But I can get relatively close by rewiring:</span><o:p></o:p></p><p class=MsoNormal><span style='font-size:14.0pt'> </span><o:p></o:p></p><p class=MsoNormal><span style='font-size:14.0pt'>String 1: -7- 200 watt @ 55.8 ea. = 390.6 v MPP</span><o:p></o:p></p><p class=MsoNormal><span style='font-size:14.0pt'>String 2: same as string 1</span><o:p></o:p></p><p class=MsoNormal><span style='font-size:14.0pt'>String 3: -6- 200 watt @ 55.8 plus -1- 235 watt @ 43.0 = 377.8 v MPP</span><o:p></o:p></p><p class=MsoNormal><span style='font-size:14.0pt'>String 4: -9- 235 watt @ 43.0 = 387 v MPP</span><o:p></o:p></p><p class=MsoNormal><span style='font-size:14.0pt'> </span><o:p></o:p></p><p class=MsoNormal><span style='font-size:14.0pt'>Under this scenario there is a delta of about 12 vdc between high and low MPP. I assume the entire array will operate at the 377.8 V MPP. I know that the 235 watt panel will be current limited also in string 3. Am I missing anything obvious in doing it like this? How will the inverter arrive at an operational MPP voltage?</span><o:p></o:p></p><p class=MsoNormal><span style='font-size:14.0pt'> </span><o:p></o:p></p><p class=MsoNormal><span style='font-size:14.0pt'>PS. In a pinch I could install a leftover 200 watt HIT I have in the shop. That way I could have -3- strings of -7- 200’s @ 390.6 v MPP, and one string of 235’s @ 387v MPP. But I would prefer not to use this panel since the frame is damaged.</span><o:p></o:p></p><p class=MsoNormal><span style='font-size:14.0pt'> </span><o:p></o:p></p><p class=MsoNormal><span style='font-size:14.0pt'>Kirk Herander</span><o:p></o:p></p><p class=MsoNormal><span style='font-size:14.0pt'>VT Solar, LLC</span><o:p></o:p></p><p class=MsoNormal><span style='font-size:14.0pt'>dba Vermont Solar Engineering</span><o:p></o:p></p><p class=MsoNormal><span style='font-size:14.0pt'>NABCEP<sup>TM </sup>Certified Inaugural Certificant</span><o:p></o:p></p><p class=MsoNormal><span style='font-size:14.0pt'>NYSERDA-eligible Installer</span><o:p></o:p></p><p class=MsoNormal><span style='font-size:14.0pt'>VT RE Incentive Program Partner</span><o:p></o:p></p><p class=MsoNormal><span style='font-size:14.0pt'>802.863.1202</span><o:p></o:p></p><p class=MsoNormal> <o:p></o:p></p></blockquote><blockquote style='margin-top:5.0pt;margin-bottom:5.0pt'><p class=MsoNormal style='margin-bottom:12.0pt'><span style='font-size:12.0pt;font-family:"Times New Roman","serif"'>_______________________________________________<br>List sponsored by Home Power magazine<br><br>List Address: <a href="mailto:RE-wrenches@lists.re-wrenches.org">RE-wrenches@lists.re-wrenches.org</a><br><br>Change email address & settings:<br><a href="http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org">http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org</a><br><br>List-Archive: <a href="http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org">http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org</a><br><br>List rules & etiquette:<br><a href="http://www.re-wrenches.org/etiquette.htm">www.re-wrenches.org/etiquette.htm</a><br><br>Check out participant bios:<br><a href="http://www.members.re-wrenches.org/">www.members.re-wrenches.org</a><o:p></o:p></span></p></blockquote></div><p class=MsoNormal style='margin-bottom:12.0pt'><span style='font-size:12.0pt;font-family:"Times New Roman","serif"'>_______________________________________________<br>List sponsored by Home Power magazine<br><br>List Address: <a href="mailto:RE-wrenches@lists.re-wrenches.org">RE-wrenches@lists.re-wrenches.org</a><br><br>Change email address & settings:<br><a href="http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org">http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org</a><br><br>List-Archive: <a href="http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org">http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org</a><br><br>List rules & etiquette:<br><a href="http://www.re-wrenches.org/etiquette.htm">www.re-wrenches.org/etiquette.htm</a><br><br>Check out participant bios:<br><a href="http://www.members.re-wrenches.org">www.members.re-wrenches.org</a><o:p></o:p></span></p></div><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Times New Roman","serif"'><o:p> </o:p></span></p></div><p class=MsoNormal style='margin-bottom:12.0pt'><span style='font-size:12.0pt;font-family:"Times New Roman","serif"'><br><br><o:p></o:p></span></p><pre>_______________________________________________<o:p></o:p></pre><pre>List sponsored by Home Power magazine<o:p></o:p></pre><pre><o:p> </o:p></pre><pre>List Address: <a href="mailto:RE-wrenches@lists.re-wrenches.org">RE-wrenches@lists.re-wrenches.org</a><o:p></o:p></pre><pre><o:p> </o:p></pre><pre>Change email address & settings:<o:p></o:p></pre><pre><a href="http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org">http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org</a><o:p></o:p></pre><pre><o:p> </o:p></pre><pre>List-Archive: <a href="http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org">http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org</a><o:p></o:p></pre><pre><o:p> </o:p></pre><pre>List rules & etiquette:<o:p></o:p></pre><pre><a href="http://www.re-wrenches.org/etiquette.htm">www.re-wrenches.org/etiquette.htm</a><o:p></o:p></pre><pre><o:p> </o:p></pre><pre>Check out participant bios:<o:p></o:p></pre><pre><a href="http://www.members.re-wrenches.org">www.members.re-wrenches.org</a><o:p></o:p></pre><pre><o:p> </o:p></pre></blockquote><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Times New Roman","serif"'><o:p> </o:p></span></p></div><div><p class=MsoNormal><span style='font-size:10.0pt;color:navy'>CONFIDENTIALITY NOTICE: This e-mail and its attachments are intended only for the use of the individual or entity who is the intended recipient and may contain information that is privileged, confidential and exempt from disclosure or any type of use under applicable law. If the reader of this e-mail is not the intended recipient, or the employee, agent, or representative responsible for delivering the e-mail to the intended recipient, you are hereby notified that any dissemination, distribution, copying, or other use of this e-mail is strictly prohibited. If you have received this e-mail in error, please reply immediately to the sender.</span> <o:p></o:p></p><p class=MsoNormal><b><span lang=DE style='font-size:13.5pt;font-family:Webdings;color:green'>P</span></b><span style='font-size:10.0pt;color:green'> Please think of the environment before printing this email</span><o:p></o:p></p></div></div></body></html>