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-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@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
_______________________________________________ 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
