<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">I have pondered this problem often. Here's my thoughts: If you could disconnect the two orientations and monitor them simultaneously, in the morning the easterly array would have a higher Vmp while the westerly array would necessarily be lower. This relationship would change throughout the day with an equilibrium being when the sun is equidistant between the two arrays. (I'm just stating the obvious here)<div><br></div><div>My question is will the lower Vmp array pull down the voltage of the higher? I notice this effect with dissimilar solar panels and MPPT controllers that many DIY RV customers have. It was stated that you may have a 2-5% loss. I can't imagine that the losses would be that low averaged for the day. </div><div><br></div><div>If the strings were split equally accross the two orientations, wont the Vmp track throughout the day and give the most production possible? Of course the inverter threshold voltage will not be met for as many hours daily but how much will this arrangement loose?<br><div><br><div> <span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div><div><div><div>Kindest Regards,</div><div><br></div><div>Larry Crutcher</div><div>Starlight Solar</div><div>11279 S. Glenwood Ave #11114</div><div>Yuma, AZ 85367</div><div>(928) 941-1660</div><div><br></div><div><a href="mailto:larry@starlightsolar.com">larry@starlightsolar.com</a></div><div><a href="http://www.starlightsolar.com">www.starlightsolar.com</a> </div></div><div><br></div><div>Retail Store: 2998 Shari, Yuma, AZ</div><div><br></div>Renewable Energy Products, Service and Installation</div><div><br></div><div><br></div></div><br></div></span><br class="Apple-interchange-newline"> </div><br><div><div>On Dec 24, 2008, at 12:41 PM, Peter Parrish wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: 'Lucida Sans'; font-size: 14px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0; "><div lang="EN-US" link="blue" vlink="purple"><div class="Section1"><div style="margin-top: 0in; margin-right: 0in; margin-left: 0in; margin-bottom: 0.0001pt; font-size: 12pt; font-family: 'Times New Roman'; "><font size="3" color="black" face="Times New Roman"><span style="font-size: 12pt; color: black; ">I don’t think this topic has been dealt with in this forum. Ocassionally we want to use a single inverter with two or more strings, each string being loaded by a single sub-array. A sub-array being defined as having a single uniform tilt angle and azimuth. All modules are identical. And each string/sub-array contains the same number of modules.</span></font></div><p class="MsoNormal" style="margin-top: 0in; margin-right: 0in; margin-left: 0in; margin-bottom: 0.0001pt; font-size: 12pt; font-family: 'Times New Roman'; "><font size="3" color="black" face="Times New Roman"><span style="font-size: 12pt; color: black; "> </span></font></p><div style="margin-top: 0in; margin-right: 0in; margin-left: 0in; margin-bottom: 0.0001pt; font-size: 12pt; font-family: 'Times New Roman'; "><font size="3" color="black" face="Times New Roman"><span style="font-size: 12pt; color: black; ">The question is: “How different can the orientation be for the different sub-arrays?</span></font></div><p class="MsoNormal" style="margin-top: 0in; margin-right: 0in; margin-left: 0in; margin-bottom: 0.0001pt; font-size: 12pt; font-family: 'Times New Roman'; "><font size="3" color="black" face="Times New Roman"><span style="font-size: 12pt; color: black; "> </span></font></p><div style="margin-top: 0in; margin-right: 0in; margin-left: 0in; margin-bottom: 0.0001pt; font-size: 12pt; font-family: 'Times New Roman'; "><font size="3" color="black" face="Times New Roman"><span style="font-size: 12pt; color: black; ">Let me pose a concrete example: Xantrex GT5.0, two strings of BP Solar SX3190s. One string has an orientation of 15 deg tilt and 188 degrees azimuth; the other has 23 degrees tilt and 139 degrees azimuth. For reasons that are difficult to explain, none of the orientation angles can be changed, at least for the purposes of this discussion. To visualize what I am talking about: the tilts are fairly close (8 degrees) and the azimuths differ by about 45 degrees.</span></font></div><p class="MsoNormal" style="margin-top: 0in; margin-right: 0in; margin-left: 0in; margin-bottom: 0.0001pt; font-size: 12pt; font-family: 'Times New Roman'; "><font size="3" color="black" face="Times New Roman"><span style="font-size: 12pt; color: black; "> </span></font></p><div style="margin-top: 0in; margin-right: 0in; margin-left: 0in; margin-bottom: 0.0001pt; font-size: 12pt; font-family: 'Times New Roman'; "><font size="3" color="black" face="Times New Roman"><span style="font-size: 12pt; color: black; ">How do I calculate the combined performance? How much power does one give up compared to using separate inverters for each sub-array/string? Are there rules of thumb as to what works and doesn’t? Do conventional inverters have algorithms that can navigate the non-ideal I-V characteristic under load? I know there was a tech bulletin from Fronius a while ago: I read it but didn’t come away with any definitive answer. I also had first hand knowledge with MPPT algorithm problems with the Fronius inverters during that time period, which caused me to discount the tech bulletin.</span></font></div><p class="MsoNormal" style="margin-top: 0in; margin-right: 0in; margin-left: 0in; margin-bottom: 0.0001pt; font-size: 12pt; font-family: 'Times New Roman'; "><font size="3" color="black" face="Times New Roman"><span style="font-size: 12pt; color: black; "> </span></font></p><div style="margin-top: 0in; margin-right: 0in; margin-left: 0in; margin-bottom: 0.0001pt; font-size: 12pt; font-family: 'Times New Roman'; "><font size="3" color="black" face="Times New Roman"><span style="font-size: 12pt; color: black; ">I am quoting a system as we speak, so my inquiry is not hypothetical in nature. Any help would be appreciated.</span></font></div><p class="MsoNormal" style="margin-top: 0in; margin-right: 0in; margin-left: 0in; margin-bottom: 0.0001pt; font-size: 12pt; font-family: 'Times New Roman'; "><font size="3" color="black" face="Times New Roman"><span style="font-size: 12pt; color: black; "> </span></font></p><div style="margin-top: 0in; margin-right: 0in; margin-left: 0in; margin-bottom: 0.0001pt; font-size: 12pt; font-family: 'Times New Roman'; "><font size="3" color="black" face="Times New Roman"><span style="font-size: 12pt; color: black; ">- Peter</span></font></div><div><p style="margin-right: 0in; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" color="navy" face="Arial"><span style="font-size: 10pt; font-family: Arial; color: navy; ">Peter T. Parrish, Ph.D., President<br>California Solar Engineering, Inc.<br>820 Cynthia Ave., Los Angeles, CA 90065<br>Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885<br>CA Lic. 854779, NABCEP Cert. 031806-26<br><a href="mailto:peter.parrish@calsolareng.com" style="color: blue; text-decoration: underline; ">peter.parrish@calsolareng.com</a></span></font><font size="2" color="blue" face="Arial"><span style="font-size: 10pt; font-family: Arial; color: blue; "></span></font></p></div></div>_______________________________________________<br>List sponsored by Home Power magazine<br><br>List Address:<span class="Apple-converted-space"> </span><a href="mailto:RE-wrenches@lists.re-wrenches.org" style="color: blue; text-decoration: underline; ">RE-wrenches@lists.re-wrenches.org</a><br><br>Options & settings:<br><a href="http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org" style="color: blue; text-decoration: underline; ">http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org</a><br><br>List-Archive:<span class="Apple-converted-space"> </span><a href="http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org" style="color: blue; text-decoration: underline; ">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" style="color: blue; text-decoration: underline; ">www.re-wrenches.org/etiquette.htm</a><br><br>Check out participant bios:<br><a href="http://www.members.re-wrenches.org" style="color: blue; text-decoration: underline; ">www.members.re-wrenches.org</a><br><br></div></span></blockquote></div><br></div></div></body></html>