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Bob-O<br>
<br>
I just re-opened the spreadsheet that I used to make my example; the
spread sheet was using 330 volts not 350 volts for the voltage drop
calculation. That error doesn't change the example in any material way.<br>
<br>
No, I haven't got any 91-watt PV modules these days. But you might get
91 watts more by selecting 200-watt panels rather than 195-watt
panels. The point is that decisions should be made by comparing
alternatives. An arbitrary choice of 1% loss regardless of costs
doesn't necessarily workout to be cost effective in near term or the
long run. <br>
<br>
Sounds like the wire prices that were quoted to you today are about 50%
of the prices in my example. That means if you are comparing 6 AWG to
4 AWG the cost comes out to $20/watt. I'm still not going there just
for the purpose reaching an arbitrary voltage drop of 1%.<br>
<br>
You can make the example extreme in the other direction too. Consider
a 50-ft circuit; otherwise the same - operating at 330 volts and 10
amps. 14 AWG will meet the 1% target. But I'd press to use at least
12 AWG, maybe even 10 with 0.3% voltage drop. <br>
<br>
Kent Osterberg<br>
Blue Mountain Solar, Inc.<br>
<br>
<br>
Bob-O Schultze wrote:
<blockquote
cite="mid:4FA7AC6E-CA2A-4296-8EB9-E9F6CB11F515@electronconnection.com"
type="cite">Kent,
<div>In fact, assuming a 33% wire mark-up and the kind of wire
pricing that we Wrenches generally get (I got quotes today), the
difference between #10 and #4 is $0.90/ft or $900/M which is how your
scenario plays out. You say that just adding more PV will cover it. I
beg to differ. You installing many 91W PVs these days? No? So you are
adding another say... 195W module? What's that add to the cost? How
about racking costs which run about $0.50/W? Module grounding? (you
should be using #6 everywhere for your GEC anyway) Hoping that you have
the room and voltage window to add a module in series and it doesn't
throw off the esthetics of the design? Inverter headroom? On and on.</div>
<div>No man, it's just a bad idea, IMHO. And, the reality is that for
most residential systems, you can achieve ≤1% on the DC side with #10
or #8 at the largest. Your scenario is a pretty arbitrary and uncommon
one to start with. I get it that you proffered it to make your point,
but... c'mon.</div>
<div>Best, Bob-O</div>
<div><br>
<div>
<div>On Apr 8, 2010, at 5:33 PM, Kent Osterberg wrote:</div>
<br class="Apple-interchange-newline">
<div bgcolor="#ffffff" text="#000000">
Bob-O<br>
<br>
Your calculation of the savings proves the point. Going from 10 AWG to
4 AWG costs $2780 today and saves $375 over the next 25 years. Now
think about how much it would cost to put in 91 watts more PV; that'll
save $375 over the next 25 years too.<br>
<br>
Granted the published wire prices are out of line. But even if lower
by a factor of five, going to 4 AWG to get down to 1% loss doesn't pay
off.<br>
<br>
Kent Osterberg<br>
Blue Mountain Solar, Inc.<br>
<br>
<br>
Bob-O Schultze wrote:
<blockquote
cite="mid:6DA46C80-9445-4852-81F9-46E6446BDF7F@electronconnection.com"
type="cite">Guys,
<div>Is it just me being dense or are none of you folks advocating
for higher VD looking at the savings over time?</div>
<div>If we assume that Kent's wire costs are correct (and even
assuming a 33% mark-up, he's paying WAY, WAY too much for wire) , the
difference in delivered watts between #10 and # 4 wire in this
situation is 91W. If I were installing this in Southern Oregon, which
is pretty average as far as peak sun hours/day go, we'd be looking at
91 x 4.5 (peak sun hours) x 365days/yr x 25yrs = 3736 KW/H. Even at
$0.10/KWH that's about $375 AT TODAY'S POWER RATES. Anyone think those
rates are going to stay the same or go down over the next 25 years?
Anybody think they won't go up by 5X? 10X? 20X?</div>
<div>So... for what and for whom are we designing these systems?</div>
<div>Bob-O</div>
<div><br>
<div>
<div>On Apr 8, 2010, at 12:40 PM, Kent Osterberg wrote:</div>
<br class="Apple-interchange-newline">
<div bgcolor="#ffffff" text="#000000">Nick,<br>
<br>
Advocating for an economic comparison between the cost of wire and the
energy saved by larger wire is not the same as advocating for high
voltage drops, or low ones either. Even with the present low prices
for PV modules and high prices for copper wire, a 100-ft long 350-volt
dc input to a 3-kW inverter should have around 1% voltage drop. Now
consider a 350-volt 10-amp PV circuit that's 500 feet long. Using 12
AWG copper the dc voltage drop would be 5.5%. Sounds like that might
be a poor wire choice, right? Look what happens as the wire size is
increased:<br>
<br>
Conductor Power $ per<br>
AWG $/ft Cost ---- Loss ---- watt saved<br>
12 0.62 $620 193W (5.5%) -- <br>
10 0.95 $950 123W (3.5%) $4.71 <br>
8 1.54 $1540 77W (2.2%) $12.83<br>
6 2.37 $2370 49W (1.4%) $29.64<br>
4 3.73 $3730 32W (0.9%) $80.00<br>
<br>
It would be reasonable to use 10 AWG copper, but before going up to 8
AWG, I'd consider buying more PV instead. Why buy a watt of power at
$12.83 when it cost less to buy a watt of PV? The conductor price used
here, just for illustration, is from Southwire's price list for
THHN/THWN wire dated 7 April 2010. In the column of conductor costs I
only considered the cost of two current carrying wires. The cost of
the equipment ground wire, conduit, connectors, etc all go up too.
That makes the dollars per watt saved look even worse.<br>
<br>
Kent Osterberg<br>
Blue Mountain Solar, Inc.<br>
<br>
<br>
Nick Soleil wrote:
<blockquote cite="mid:904885.96037.qm@web44903.mail.sp1.yahoo.com"
type="cite">
<style type="text/css"><!-- DIV {margin:0px;} --></style>
<div
style="font-family: arial,helvetica,sans-serif; font-size: 12pt;">I
feel that it is best to maintain a 1.5% voltage drop on the AC and DC.
However, I was just sizing conductors for a 400 KW project, with the
array 1000' from the main service panel. With AC modules, I would have
needed 5-Parallel runs of 700MCM at 208VAC (20 wires at 700MCM for
1.5%VD!) The cost would have been over 100K, which was cost
prohibitive. However, by running DC wiring, and utilzing AL, we were
able to maintain 1.5 VDC drop without being too expensive (yet still
expensive.)<br>
<div> </div>
Nick Soleil<br>
Project Manager<br>
Advanced Alternative Energy Solutions, LLC<br>
PO Box 657<br>
Petaluma, CA 94953<br>
Cell: 707-321-2937<br>
Office: 707-789-9537<br>
Fax: 707-769-9037</div>
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