<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Also consider that most people are figuring volt drop at a wire temperature of 167 deg F (75C). That's really hot, and most of the time the wire will be much cooler, and therefore the volt drop will be less.<div>(use the fine print note #2, NEC table 8 to adjust down for cooler temperature)</div><div>William's time analysis is very interesting as well: when considering wire losses for a continuous 24/7 load, it is roughly 4 times more important to reduce the losses than the PV wiring. Likewise a load that is only on 5 min/ day doesn't make near as much sense to oversize the wire. I added this time factor to my spreadsheet for calculating economics.</div><div><br><div>
<span class="Apple-style-span" style="border-collapse: separate; border-spacing: 0px 0px; 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; text-align: auto; -khtml-text-decorations-in-effect: none; text-indent: 0px; -apple-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><div>R. Walters</div><div><a href="mailto:ray@solarray.com">ray@solarray.com</a></div><div>Solar Engineer</div><div><br class="khtml-block-placeholder"></div><div><br class="khtml-block-placeholder"></div><br class="Apple-interchange-newline"></span>
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<br><div><div>On Apr 9, 2010, at 8:44 AM, William Miller wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div>
<font size="3">Friends:<br><br>
Forgive me if this point has already been made:<br><br>
When designing PV feeders, one typically looks at the Impp of an array
for current specifications. Impp is rarely achieved, however --
only a handful of days per year and for only a short period of time
per day. This is particularly true for a fixed
array.<br><br>
I took the hour-by-hour data from the PV watts tool, subtracted out the
zero values (night time) and averaged the remaining values. The
result was about 50%.<br><br>
Therefore, a 2% VD at Impp is actually a 1% VD on average. This
gives a bit more headroom in any PV feeder design.<br><br>
William Miller<br><br>
<br>
At 04:25 AM 4/9/2010, you wrote:<br>
</font><blockquote type="cite" class="cite" cite=""><font size="3">IMHO it seems like we're all really
on the same page here...... trying to make<br>
the the most out of the the resources we have available to work
with......sun<br>
hours, pv, copper, labor, dollars, etc. Job specifics come into play.
There are<br>
definitely times when a detailed cost/ benefit analysis is called for.
Many<br>
other times, let's not miss the forest for the trees, an increase in wire
size<br>
to avoid waste of other aforementioned resources, is low hanging fruit.
As a<br>
percentage of the overall system cost, the decision is a no
-brainer.<br><br>
Dick Ratico<br>
Solarwind Electic</font></blockquote></div>
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