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<DIV><FONT size=2 face=Calibri>The original rationale was probably due more to
solar panel costs more than anything else - at a time when solar was $10-15 a
watt, and copper was cheap it made sense.</FONT></DIV>
<DIV><FONT size=2 face=Calibri></FONT> </DIV>
<DIV><FONT size=2 face=Calibri>But now that solar panels cost 1/5th as much and
copper wire is 4x as much, probably not so much now. Nowadays it is quite often
much more economical on systems with long wire runs to add more panel than to
use bigger wire.</FONT></DIV>
<DIV><FONT size=2 face=Calibri></FONT> </DIV>
<DIV><FONT size=2 face=Calibri>Also, when that "standard" was adopted, there
were still a lot of panels made in the 15.5 to 16.5 volt range, and 2/10th
to 4/10th of a volt drop was more important to battery life and charging in hot
weather, so that may have been a factor also.</FONT></DIV>
<DIV><FONT size=2 face=Calibri></FONT> </DIV>
<DIV>..................................................................................................<BR>Northern
Arizona Wind & Sun - Electricity From The Sun Since 1979<BR>Solar Discussion
Forum: <A
href="http://www.wind-sun.com/ForumVB/">http://www.wind-sun.com/ForumVB/</A><BR>..................................................................................................</DIV>
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<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="FONT: 10pt arial; BACKGROUND: #e4e4e4; font-color: black"><B>From:</B>
<A title=kent@coveoregon.com href="mailto:kent@coveoregon.com">Kent
Osterberg</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A
title=re-wrenches@lists.re-wrenches.org
href="mailto:re-wrenches@lists.re-wrenches.org">RE-wrenches</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Monday, April 12, 2010 10:51
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: [RE-wrenches] DC wire
sizing</DIV>
<DIV><BR></DIV>I know you wouldn't, Warren. Because it is much more
economical (that means more kWh/$) to use a MPPT controller. But you
would run a 100-volt 30-amp PV array to a MPPT charge controller that is 150
feet away. For that distance, it takes 1/0 wire to get the wire loss
down to 1%. I'd probably settle for using 3 AWG copper with 2%
loss. With the smaller wire, the looses are 29 watts more, but the
system cost is less by at least $700. At $700/29 watts = $24/watt, the
1/0 wire is not a good choice.<BR><BR>My question is: what is the rational for
using 1% loss as the design objective. Why not 1/2%? Why not
2%?<BR>So far no one has offered an answer to that question; despite many
claiming that 1% or 1.5% is always their design objective.<BR><BR>In Home
Power issue 104, December 2004 - January 2005, I showed that striving for low
voltage drops in low-voltage systems doesn't mean you've got a good
(economical) design. The spreadsheet I created for that article is no
longer available, but one that is easier to use is available from Ray Walters'
web site. In SolarPro 3.2, February - March 2010, Blake Gleason shows an
example where upsizing the wire size to get 2.6% loss is not
economical.<BR><BR>Kent Osterberg<BR>Blue Mountain Solar,
Inc.<BR><BR><BR>Warren Lauzon wrote:
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<DIV><FONT size=2 face=Calibri>I would never design such a system. That is
what MPPT controllers are for. 10 years ago we did not have that choice, but
now we do, so there is no reason at all to design a 40 amp 12 volt array
circuit.</FONT></DIV>
<DIV> </DIV>
<DIV>..................................................................................................<BR>Northern
Arizona Wind & Sun - Electricity From The Sun Since 1979<BR>Solar
Discussion Forum: <A href="http://www.wind-sun.com/ForumVB/"
moz-do-not-send="true">http://www.wind-sun.com/ForumVB/</A><BR>..................................................................................................</DIV>
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<DIV
style="FONT: 10pt arial; font-size-adjust: none; font-stretch: normal">-----
Original Message ----- </DIV>
<DIV
style="FONT: 10pt arial; BACKGROUND: rgb(228,228,228) 0% 50%; font-size-adjust: none; font-stretch: normal; -moz-background-clip: -moz-initial; -moz-background-origin: -moz-initial; -moz-background-inline-policy: -moz-initial"><B>From:</B>
<A title=kent@coveoregon.com href="mailto:kent@coveoregon.com"
moz-do-not-send="true">Kent Osterberg</A> </DIV>
<DIV
style="FONT: 10pt arial; font-size-adjust: none; font-stretch: normal"><B>To:</B>
<A title=re-wrenches@lists.re-wrenches.org
href="mailto:re-wrenches@lists.re-wrenches.org"
moz-do-not-send="true">Wrenches</A> </DIV>
<DIV
style="FONT: 10pt arial; font-size-adjust: none; font-stretch: normal"><B>Sent:</B>
Saturday, April 10, 2010 9:22 AM</DIV>
<DIV
style="FONT: 10pt arial; font-size-adjust: none; font-stretch: normal"><B>Subject:</B>
[RE-wrenches] DC wire sizing</DIV>
<DIV><BR></DIV>Here's my challenge to all of you that want to design for
1% or 1.5% voltage drop all the time:<BR>Take a 50-ft circuit carrying 40
amps at 12 volts, going to a C40 charge controller, select your wire size
for 1% or 1.5% loss. You know that's not a practical solution. I
know that it makes more sense to replace the charge controller and run the
PV circuit at a higher voltage.<BR><BR><B>At % loss did it become
impractical?</B> Ray's answer and my answer is "when there is a
cheaper alternative -- lower cost per watt out or lower cost per kWh over
the project life." And that answer works even when you are
considering a 400-kW PV array that is 1000 feet away.<BR><BR>Kent
Osterberg<BR>Blue Mountain Solar, Inc.<BR></BLOCKQUOTE></BLOCKQUOTE>
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