[RE-wrenches] calculating low string voltage

[Bill Brooks]

Ray,

There is an explanation on the www.solarabcs.org/permitting webpage for the
interactive solar map. The 2% ASHRAE data represents 14 hours in a
month-meaning temperature will be at or above that value for 14 hours in a
typical month. This is likely to correspond to at least one 3-hour timeframe
which is considered "continuous" in the NEC. The Copper Development
Association has chosen this number for ambient temperature calculations in
the NEC. The NEC Handbook (not the NEC) uses this number in their example
problems.         

The 0.4% ASHRAE date represents 3 hours in a month. It is much more
conservative number. I put it in the data to provide a context for the 2%
number and it allows engineers to consider a more conservative number.

Of course, the mean extreme minimum drybulb temperature is also on that
website for 690.7 max system voltage calculations. Enjoy-its free thanks to
SolarABCs.

Bill.

 

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Ray Walters
Sent: Thursday, December 01, 2011 3:58 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] calculating low string voltage

 

Fantastic Info everyone, I think I've got a full grasp on this topic now,
from using the correct coefficient to the correct weather data, to the
adders for installation type, and a nice link to the applicable data without
spending $180 for the ASHRAE book.  

I'm guessing the 2% number is 2%  of the time year round 24/7, not 2% of the
time the sun is shining, so losses could be higher than 2% of production?
Sorry to keep asking questions, but I know my class will probably ask the
same thing.

Ray

On 12/1/2011 2:57 PM, Gary Willett wrote: 

RAY:

This "Solar Reference Guide Map" web site is also linked to on the SolarABCs
site and provides the ASHRAE 0.4%  & 2% high temperatures, as well as the PV
module max temp based on distance above the roof (0.5, 3.5, and 12").

http://www.solarabcs.org/about/publications/reports/expedited-permit/map/ind
ex.html

Regards,

Gary Willett, PE


On 12/1/2011 14:56, Gary Willett wrote: 

Ray:  

Look at Appendix F in the Expedited Permit Process for PV Systems - A
Standardized Process for the Review of Small-Scale PV Systems Prepared by
Bill Brooks, P.E. Brooks Engineering

This document provides the ASHRE temperatures for a lot of locations around
the USA.

http://www.solarabcs.org/about/publications/reports/expedited-permit/pdfs/Ex
permitprocess.pdf



Regards,


Gary Willett, PE

 
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