[RE-wrenches] calculating DC voltage drop

[Michael Kelly]

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

mike at solren.com

www.solren.com <http://www.solren.com/> 

 

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at 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

ray at 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 at 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/> 

 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20100722/9ad86da9/attachment-0003.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image001.jpg
Type: image/jpeg
Size: 2863 bytes
Desc: not available
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20100722/9ad86da9/attachment-0003.jpg>