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 T toplogo 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 <http://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 <http://www.members.re-wrenches.org/>
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