Hi Dana; I'd say that's a bit overkill for today's market. That money could be making more power, not just preventing losses. Definitely a law of diminishing returns on wire sizing. 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. I'm only using this ridiculous example to show, that at some point, we all spend money on more PV, not bigger wire. 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. If copper was still at 20th century prices, and PV were $10/ watt, your 1% might very well be the right answer.
( this is also the point where Bob-O starts hammering me, so I'd better run. ☹☺) R. Walters r...@solarray.com Solar Engineer On Jul 22, 2010, at 2:58 PM, Dana wrote: > For array to power center or Inverter; I use 125% of amps @ max power and run > the wire calculations at 1% VD. > > We have set Fluke meters on clamped on @ both ends and talked with radios & > compared the readings. We have not seen any noticeable VD down to .00vdc. > > Perhaps overkill? > > Thanks, Dana Orzel > > Great Solar Works, Inc > E - d...@solarwork.com > V - 970.626.5253 > F - 970.626.4140 > C - 970.209.4076 > web - www.solarwork.com > > "Responsible Technologies for Responsible People since 1988" > > From: re-wrenches-boun...@lists.re-wrenches.org > [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Michael Kelly > Sent: Thursday, July 22, 2010 2:13 PM > To: 'RE-wrenches' > Subject: Re: [RE-wrenches] calculating DC voltage drop > > Hi All, > > I agree with Ray with the exception that I use Imp*1.25 in my calculations. > I developed a simple spreadsheet for either fixed conductor size or for fixed > voltage drop. You can feel free to use it by downloading here: > http://www.mechanicalmike.com/solar/DC_Voltage_Drop_Calculations_Template_04_20_2010.xltx. > > - Mike > --- > Michael Kelly > Applications Engineer > NABCEP Certified Solar PV Installer ™ > <image001.jpg> > Solectria Renewables, LLC > 360 Merrimack St. > Building 9, Floor 2 > Lawrence, MA 01843 > Phone: 978-683-9700 ext. 167 > Fax: 978-683-9702 > m...@solren.com > www.solren.com > > From: re-wrenches-boun...@lists.re-wrenches.org > [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of R Ray Walters > Sent: Thursday, July 22, 2010 3:45 PM > To: RE-wrenches > Subject: Re: [RE-wrenches] calculating DC voltage drop > > I use actual operating current, without multipliers. I also use actual > temperatures, not the worst case temperatures that many use. > I created a spread sheet that uses the NEC adjustments for wire temperature, > (see NEC chapter 9, table 8, FPN 2) > It makes quite a difference! > Volt drop and the accompanying loss of energy production needs to be looked > at realistically under normal operating conditions. Adding worst case > multipliers is necessary for sizing cables and breakers for safety, but it > isn't appropriate when calculating energy losses. We shouldn't do an energy > loss analysis for a situation that might never occur, or for only a very > small % of the time. > A correct analysis will reflect actual losses over the lifetime of the > system, so that an informed economic decision can be made. Especially on > larger systems with long runs, its worth it to you and the client to use real > world numbers, not blind over sizing. > I got into this over a decade ago, when I noticed that actual measured volt > drop was much less than calculated, now my calculations match real > measurements. > > R. Walters > r...@solarray.com > Solar Engineer > > > > > > On Jul 22, 2010, at 1:22 PM, Marco Mangelsdorf wrote: > > > When calculating the voltage drop from a PV array to the inverter, what’s the > most common accepted practice? To use the Isc X 1.25 or 1.56 as the > multiplier? > > Thanks, > marco > > _______________________________________________ > List sponsored by Home Power magazine > > List Address: RE-wrenches@lists.re-wrenches.org > > Options & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out participant bios: > www.members.re-wrenches.org > > > No virus found in this incoming message. > Checked by AVG - www.avg.com > Version: 9.0.851 / Virus Database: 271.1.1/3021 - Release Date: 07/22/10 > 00:36:00 > > _______________________________________________ > List sponsored by Home Power magazine > > List Address: RE-wrenches@lists.re-wrenches.org > > Options & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out participant bios: > www.members.re-wrenches.org >
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