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<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>All,<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>This is all very interesting, but on the dc side, it is
primarily an issue of energy loss for large grid-connected systems. My rule is
2% voltage drop for dc side and 1% for ac side.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>When we talk about dc % voltage drop, most of what has
been discussed in this thread is instantaneous voltage drop. That is
interesting, but year-round voltage losses are more important. There are two
ways to get this:<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoListParagraph style='text-indent:-.25in;mso-list:l0 level1 lfo1'><![if !supportLists]><span
style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><span
style='mso-list:Ignore'>1.<span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Use a simulation program like PVSyst to calculate the voltage
drop every hour of the day and give you an overall loss for the year.<o:p></o:p></span></p>
<p class=MsoListParagraph style='text-indent:-.25in;mso-list:l0 level1 lfo1'><![if !supportLists]><span
style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><span
style='mso-list:Ignore'>2.<span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Take 80% of Imp for the array and use that current with the nominal
voltage of the array (330 Volts for a 600V array). The reason for 80% of Imp is
that half of the energy is delivered above this number and half below. It makes
an ideal “nominal” current of the array.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>By using one of these methods, you will calculate the accurate
energy loss on the dc side.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Bill.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
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>Allan
Sindelar<br>
<b>Sent:</b> Thursday, July 22, 2010 3:12 PM<br>
<b>To:</b> mike@solren.com; RE-wrenches<br>
<b>Subject:</b> Re: [RE-wrenches] calculating DC voltage drop<o:p></o:p></span></p>
</div>
</div>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal style='margin-bottom:12.0pt'>Mike,<br>
I would respectfully challenge both reasons ;^)} . The responses already posted
today cover them: you don't need to compensate for intermittent high-insolation
conditions when sizing for voltage loss, as this is not a Code issue; Code
addresses ampacity and OCP issues. And being conservative means you add
unnecessarily to wire cost (sometimes substantially at 25% greater current)
when that money could be better spent on more PV, with an ultimately greater
annualized return of total energy per $$ spent. Ray Walters' recent posts cover
this well.<o:p></o:p></p>
<div>
<p class=MsoNormal><span class=il><b>Allan</b></span><b> Sindelar</b><span
style='font-size:10.0pt'><br>
<a href="mailto:Allan@positiveenergysolar.com" target="_blank"><span class=il>Allan</span>@positiveenergysolar.com</a><br>
NABCEP Certified Photovoltaic Installer<br>
EE98J Journeyman Electrician<br>
<b>Positive Energy, Inc.</b><br>
3201 Calle Marie<br>
Santa Fe, New Mexico 87507<br>
<b>505 424-1112</b><br>
<a href="http://www.positiveenergysolar.com/" target="_blank">www.positiveenergysolar.com</a></span><o:p></o:p></p>
</div>
<p class=MsoNormal><br>
On 7/22/2010 3:53 PM, Michael Kelly wrote: <o:p></o:p></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:windowtext'>Allan,</span><o:p></o:p></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:windowtext'> </span><o:p></o:p></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:windowtext'>I use Imp*1.25 because NEC calls out a 125% adder for
unexpected high-insolation conditions (snowscapes, cloud effect, yellow houses
next door, etc). And because I am an engineer and like to be conservative
:).</span><o:p></o:p></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:windowtext'> </span><o:p></o:p></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:windowtext'>-Mike</span><o:p></o:p></p>
<div>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:windowtext'>---</span><o:p></o:p></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:windowtext'>Michael Kelly<br>
Applications Engineer</span><o:p></o:p></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:windowtext'>NABCEP Certified Solar PV Installer ™</span><o:p></o:p></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:windowtext'><img border=0 width=150 height=36 id="Picture_x0020_1"
src="cid:image001.jpg@01CB29BF.0543E8A0" alt=toplogo><br>
Solectria Renewables, LLC</span><o:p></o:p></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:windowtext'>360 Merrimack St.</span><o:p></o:p></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:windowtext'>Building 9, Floor 2</span><o:p></o:p></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:windowtext'>Lawrence, MA 01843<br>
Phone: 978-683-9700 ext. 167<br>
Fax: 978-683-9702</span><o:p></o:p></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:windowtext'><a href="mailto:mike@solren.com">mike@solren.com</a></span><o:p></o:p></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:windowtext'><a href="http://www.solren.com/">www.solren.com</a></span><o:p></o:p></p>
</div>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:windowtext'> </span><o:p></o:p></p>
<div>
<div style='border:none;border-top:solid windowtext 1.0pt;padding:3.0pt 0in 0in 0in;
border-color:-moz-use-text-color -moz-use-text-color'>
<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'> Allan Sindelar [<a
href="mailto:allan@positiveenergysolar.com">mailto:allan@positiveenergysolar.com</a>]
<br>
<b>Sent:</b> Thursday, July 22, 2010 5:26 PM<br>
<b>To:</b> <a href="mailto:mike@solren.com">mike@solren.com</a>; RE-wrenches<br>
<b>Subject:</b> Re: [RE-wrenches] calculating DC voltage drop</span><o:p></o:p></p>
</div>
</div>
<p class=MsoNormal> <o:p></o:p></p>
<p class=MsoNormal style='margin-bottom:12.0pt'>Mike,<br>
Why do you make this exception, please?<o:p></o:p></p>
<div>
<p class=MsoNormal><span class=il><b>Allan</b></span><b> Sindelar</b><span
style='font-size:10.0pt'><br>
<a href="mailto:Allan@positiveenergysolar.com" target="_blank"><span class=il>Allan</span>@positiveenergysolar.com</a><br>
NABCEP Certified Photovoltaic Installer<br>
EE98J Journeyman Electrician<br>
<b>Positive Energy, Inc.</b><br>
3201 Calle Marie<br>
Santa Fe, New Mexico 87507<br>
<b>505 424-1112</b><br>
<a href="http://www.positiveenergysolar.com/" target="_blank">www.positiveenergysolar.com</a></span><o:p></o:p></p>
</div>
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