[RE-wrenches] DC wire sizing

[Nick Soleil]

I haven't checked my e-mail for days, but have to add to this topic.
    Hi Kent:
In a few isolated situations, a cost analysis may be done to justify not designing at 1-2% DC Voltage drops, but for most systems the cost of the wire is less than the cost of the PV.  I buy my wire for about 1/4 the cost of your analysis.  I would ask you to look closer at your next design, and consider designing at a lower voltage drop than 3%.  

 Nick Soleil
Project Manager
Advanced Alternative Energy Solutions, LLC
PO Box 657
Petaluma, CA 94953
Cell:   707-321-2937
Office: 707-789-9537
Fax:    707-769-9037




________________________________
From: Bob-O Schultze <bob-o at electronconnection.com>
To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
Sent: Sat, April 10, 2010 10:26:56 AM
Subject: Re: [RE-wrenches] DC wire sizing

Of course it's not a practical solution, which is why we strived for (but rarely got) 2% VD on low voltage situations as I said in my first post. The obvious reply to this post is that your scenario isn't real world anymore. MPPT controllers fixed that. Or perhaps you advocate that MPPT controllers are just too expensive too? I could easily come up with a scenario where a C40 and big wire is less expensive than using MPPT and smaller wire. But is that good design? I don't think so.
My point -and one which you apparently dismiss out of hand- is just that cheaper is not always better. Good design and best practices rarely go hand in hand with cheaper.
Waste is waste. Along those same lines, I'll repeat something a friend of mine recently said, "If you like getting your oil from Saudi Arabia, you're gonna love getting your PV from China. " It's cheaper, right?
Ya know?
Bob-O


On Apr 10, 2010, at 9:22 AM, Kent Osterberg wrote:

Here's my challenge to all of you that want to design for 1% or 1.5%
voltage drop all the time:
Take a 50-ft circuit carrying 40 amps at 12 volts, going to a C40
charge controller, select your wire size for 1% or 1.5% loss. You know
that's not a practical solution.  I know that it makes more sense to
replace the charge controller and run the PV circuit at a higher
voltage.

At % loss did it become impractical?  Ray's answer and my answer
is "when there is a cheaper alternative -- lower cost per watt out or
lower cost per kWh over the project life."  And that answer works even
when you are considering a 400-kW PV array that is 1000 feet away.

Kent Osterberg
Blue Mountain Solar, Inc.


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