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Dana,<br>
<br>
2.6% voltage drop also means 2.6% power loss. To go from 2.6% loss to
1.6% loss you gain about 4.1 watts for the extra $22. That is
$5.36/watt so it probably makes sense to use the larger wire. Now
compare 1.6% and 0.4%: you gain about 4.9 watts for the extra $140,
that's $28.57/watt. If you can buy and install PV for much less than
that, how can you justify such little gain from the extra wire cost? 2
or 3 AWG may be worth it, but it sure doesn't look like 1 AWG is a
smart choice.<br>
<br>
Kent Osterberg<br>
Blue Mountain Solar<br>
<br>
<br>
Dana wrote:
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<p class="MsoNormal"><span
style="font-size: 14pt; font-family: "Century Gothic","sans-serif";">Ray,
<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size: 14pt; font-family: "Century Gothic","sans-serif";"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size: 14pt; font-family: "Century Gothic","sans-serif";">The
$ could be making power I agree on a large scale project. <o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size: 14pt; font-family: "Century Gothic","sans-serif";"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size: 14pt; font-family: "Century Gothic","sans-serif";">The
point here is where is the cutoff point?<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size: 14pt; font-family: "Century Gothic","sans-serif";"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size: 14pt; font-family: "Century Gothic","sans-serif";">Let’s
take a very small cabin system:<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size: 14pt; font-family: "Century Gothic","sans-serif";">410
watts or 13 amps [inc.1.25%]@ 44VOC, over a 90’ one-way run.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size: 14pt; font-family: "Century Gothic","sans-serif";">Utilizing
and Electro-calc with 2008 NEC installed<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size: 14pt; font-family: "Century Gothic","sans-serif";"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size: 14pt; font-family: "Century Gothic","sans-serif";">2.6%VD
– 1.1vd requires a pair #6 Thhn @ $0.66/ft = $118 for 180’wire @ whole
sale
price.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size: 14pt; font-family: "Century Gothic","sans-serif";"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size: 14pt; font-family: "Century Gothic","sans-serif";">1.6%VD
– 0.7vd requires a pair #4 Thhn @ $0.78/ft = $140 for 180’wire @ whole
sale.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size: 14pt; font-family: "Century Gothic","sans-serif";"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size: 14pt; font-family: "Century Gothic","sans-serif";">0.4%VD
– 0.4vd requires a pair #1 Thhn @ $1.55/ft = $279for 180’ wire @ whole
sale.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size: 14pt; font-family: "Century Gothic","sans-serif";"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size: 14pt; font-family: "Century Gothic","sans-serif";">I
grant you the cost savings up front, and MPPT covers a lot errors these
days,
but where do we say what is better?<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size: 14pt; font-family: "Century Gothic","sans-serif";"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size: 14pt; font-family: "Century Gothic","sans-serif";">So
my question is-<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size: 14pt; font-family: "Century Gothic","sans-serif";">In
MPPT what is .3volt drop worth VS 0.7vd VS 1.1vd worth in MPPT charge
capabilities over the life of the system? <o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size: 14pt; font-family: "Century Gothic","sans-serif";">Weather
it is a utility scale project or a small cabin.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size: 14pt; font-family: "Century Gothic","sans-serif";"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size: 14pt; font-family: "Century Gothic","sans-serif";"><o:p> </o:p></span></p>
<div>
<p class="MsoNormal"><span
style="font-family: "Century Gothic","sans-serif";">Thanks,
Dana Orzel<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-family: "Century Gothic","sans-serif";"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-family: "Century Gothic","sans-serif";">Great
Solar Works, Inc<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-family: "Century Gothic","sans-serif";">E -
<a class="moz-txt-link-abbreviated" href="mailto:dana@solarwork.com">dana@solarwork.com</a><o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-family: "Century Gothic","sans-serif";">V -
970.626.5253<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-family: "Century Gothic","sans-serif";">F -
970.626.4140<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-family: "Century Gothic","sans-serif";">C -
970.209.4076<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-family: "Century Gothic","sans-serif";">web
- <a class="moz-txt-link-abbreviated" href="http://www.solarwork.com">www.solarwork.com</a><o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-family: "Century Gothic","sans-serif";"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-family: "Century Gothic","sans-serif";">"Responsible
Technologies for Responsible People since 1988"</span><span
style="font-size: 11pt; font-family: "Calibri","sans-serif";"><o:p></o:p></span></p>
</div>
<p class="MsoNormal"><span
style="font-size: 14pt; font-family: "Century Gothic","sans-serif";"><o:p> </o:p></span></p>
<div>
<div
style="border-style: solid none none; border-color: rgb(181, 196, 223) -moz-use-text-color -moz-use-text-color; border-width: 1pt medium medium; padding: 3pt 0in 0in;">
<p class="MsoNormal" style="margin-left: 0.5in;"><b><span
style="font-size: 10pt; font-family: "Tahoma","sans-serif";">From:</span></b><span
style="font-size: 10pt; font-family: "Tahoma","sans-serif";">
<a class="moz-txt-link-abbreviated" href="mailto:re-wrenches-bounces@lists.re-wrenches.org">re-wrenches-bounces@lists.re-wrenches.org</a>
[<a class="moz-txt-link-freetext" href="mailto:re-wrenches-bounces@lists.re-wrenches.org">mailto:re-wrenches-bounces@lists.re-wrenches.org</a>] <b>On Behalf Of </b>R
Ray
Walters<br>
<b>Sent:</b> Thursday, July 22, 2010 3:30 PM<br>
<b>To:</b> RE-wrenches<br>
<b>Subject:</b> Re: [RE-wrenches] calculating DC voltage drop<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal" style="margin-left: 0.5in;"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-left: 0.5in;">Hi Dana;<o:p></o:p></p>
<div>
<p class="MsoNormal" style="margin-left: 0.5in;"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal" style="margin-left: 0.5in;">I'd say that's a bit
overkill for
today's market. That money could be making more power, not just
preventing
losses. <o:p></o:p></p>
<div>
<div>
<p class="MsoNormal" style="margin-left: 0.5in;">Definitely a law of
diminishing
returns on wire sizing. <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal" style="margin-left: 0.5in;">If you allocated 50%
of the budget
to wire, and 50% to PV, your losses would be very low, (immeasurable
but
unfortunately still there) but your total system production vs. the
money spent
would be terrible.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal" style="margin-left: 0.5in;">I'm only using this
ridiculous
example to show, that at some point, we all spend money on more PV, not
bigger
wire. <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal" style="margin-left: 0.5in;">I pick that point
based on sound
economic analysis, not some over applied rule of thumb. As copper costs
rise,
and PV gets cheaper, that point moves up. <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal" style="margin-left: 0.5in;">If copper was still
at 20th century
prices, and PV were $10/ watt, your 1% might very well be the right
answer.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal" style="margin-left: 0.5in;"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal" style="margin-left: 0.5in;">( this is also the
point where
Bob-O starts hammering me, so I'd better run. ??)<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal" style="margin-left: 0.5in;"><o:p> </o:p></p>
</div>
<div>
<div>
<div>
<div>
<p class="MsoNormal" style="margin-left: 0.5in;"><span
style="font-size: 9pt; font-family: "Helvetica","sans-serif"; color: black;">R.
Walters<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal" style="margin-left: 0.5in;"><span
style="font-size: 9pt; font-family: "Helvetica","sans-serif"; color: black;"><a
moz-do-not-send="true" href="mailto:ray@solarray.com">ray@solarray.com</a><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal" style="margin-left: 0.5in;"><span
style="font-size: 9pt; font-family: "Helvetica","sans-serif"; color: black;">Solar
Engineer<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal" style="margin-left: 0.5in;"><span
style="font-size: 9pt; font-family: "Helvetica","sans-serif"; color: black;"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal" style="margin-left: 0.5in;"><span
style="font-size: 9pt; font-family: "Helvetica","sans-serif"; color: black;"><o:p> </o:p></span></p>
</div>
<p class="MsoNormal" style="margin-left: 0.5in;"><span
style="font-size: 9pt; font-family: "Helvetica","sans-serif"; color: black;"><br>
<br>
</span><o:p></o:p></p>
</div>
</div>
</div>
</div>
</div>
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