[RE Marketing] 400 ft DC voltage drop [RE-wrenches]

[Jeff Clearwater, Village Power Design]

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Hi Steve,

William' approach is exactly it.  We use to do 1% at Vmp but as 
copper prices increased we did a more careful analysis of the peak vs 
average issue and now use 1.5%  But as he says make sure that's from 
panel to inverter, not just from combiner to disconnect.  I do take a 
look at Vmin (the inverter's MPPT min) for the worst case scenario 
but that usually doesn't go over 2% if Vmp is at 1.5% or better.

That said if the run is short or the pull easy I tend to bump up a 
size to maximize those precious PV watts which usually puts me back 
in the 1% range at Vmp - but if the run is long and the cost starts 
going up - William's perspective is what we use.

Hope that helps!

Jeff Clearwater
Village Power Design


>Steve:
>
>I'd say E because high temp Emp will occur at lower output amperage. 
>I doubt the difference between D or E will be significant and Voc 
>does not count.
>
>Consider this concept:  Rated current occurs rarely, if ever. 
>Assume, though, it occurs at noon.  The rest of the day presents 
>varying degrees of lesser current.  What is the area under the 
>curve?  My research indicates it is 50% of the peak amperage.
>
>What does this mean?  It means that if you design a PV feeder for 2% 
>voltage drop at peak output, it will average 1% over the day.  Or, 
>design criteria for PV feeders is only half as important as we think 
>it is.  (Don't forget to quantify cumulative loses throughout all 
>feeders and components, however.)
>
>William Miller
>
>
>At 10:18 PM 4/30/2008, you wrote:
>>I have a 400 foot run on an output circuit to combiner, 23.5 amps.
>>Should the DC VOLTAGE that is used as the system voltage to calculate
>>voltage drop be:
>>A) Voc at low temperature
>>B) Voc at high temperature
>>C) Nameplate Voc
>>D) Vmp at high Temperature
>>E) Nameplate Vmp
>>
>


-- 
~~~~~~~~~~~~~
Jeff Clearwater
Village Power Design
Sustainable Energy & Water Solutions for Home & Village
http://www.villagepower.com
gosolar at villagepower.com
NABCEP (tm) Certified Solar PV Installer

Voice: 413-259-3776
Fax: 413-825-0703
65 Schoolhouse Rd
Amherst, MA 01002
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~`~


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