http://www.copper.org/applications/electrical/building/pdf/rooftop.pdf
³ASHRAE bases its ³warm-season temperature conditions² for each city on annual percentiles of 0.4%, 2 %, 5% and 10%. As an example, the June 2.0% dry-bulb design temperature for Atlanta is 91.7°F. Therefore, based on a 30-day month (i.e., 720 hours), the actual temperatures can be expected to exceed 91.7°F for total of 14 hours a month. The corresponding 5.0% design temperature (89.3°F) can be expected to be exceeded for 36 hours a month; while the 0.4% design temperature (94.7°F) can be expected to be exceeded for 3 hours a month.² On 12/1/11 5:57 PM, "Ray Walters" <r...@solarray.com> wrote: > 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/inde >> x.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 >>> >>> >>> >>> On 12/1/2011 14:48, Ray Walters wrote: >>>> That's more detailed info, but I still am wondering what ambient temp to >>>> apply (which AHSRAE #) with the temp adder. Daryl suggested using a 2% >>>> high temp. Also, where are you all getting your weather data? I found the >>>> NEC suggested ASHRAE manual to be close to $200. That's a bit much just to >>>> get a couple of numbers for our design. >>>> It seems this calculation of low voltage is far from being entirely >>>> codified, and I'm trying to standardize it somewhat for my PV class. Non of >>>> the design manuals I have currently are even close to this level of >>>> complexity, yet this is obviously an important calculation. Should I >>>> suggest that my students just use the inverter manufacturers' online tools, >>>> and forget about trying to run this voltage calc themselves? >>>> >>>> Thanks, >>>> >>>> Ray >>>> >>>> On 12/1/2011 6:30 AM, Dave Click wrote: >>>> >>>>> At an SMA training last year they recommended the following temperature >>>>> adders: >>>>> >>>>> Open field: +22°C >>>>> Rooftop, lots of ventilation: +28°C >>>>> Rooftop, some ventilation: +29°C >>>>> Rooftop, little ventilation: +32°C >>>>> Rooftop BIPV, no ventilation: +43°C >>>>> Façade, some ventilation: +35°C >>>>> Façade, little ventilation: +39°C >>>>> Façade BIPV, no ventilation: +55°C >>>>> >>>>> For your Sanyo project, I'd agree that the pole mount would be a good fit >>>>> and +25C would seem to be OK. As you know, the 301VDC VMP on an inverter >>>>> with a 300V+ tracking window wouldn't work very well during the summers >>>>> for very long. My own rooftop system has a design VMP of around 294 at 70C >>>>> module temperature and I've seen it a bit lower than that on a sunny day-- >>>>> I think it's because in irradiances below 1000Wm/2, the modules can still >>>>> get plenty hot but the lower irradiance doesn't bring the VMP up to 100%. >>>>> So all told, maybe plan for an array minimum of: >>>>> >>>>> Inverter Tracking Minimum >>>>> /0.85 (degradation and voltage tolerance) >>>>> /0.95 (effect I just described) >>>>> /0.825 (60C operating temp) >>>>> = minimum string VMP at STC >>>>> >>>>> (similar to what Bill said) >>>>> >>>>> On 2011/11/30 11:04, Kirk Herander wrote: >>>>> >>>>>> Thanks for all the good response. Speaking of monkey wrenches, these are >>>>>> Sanyo HIT Double panels, mounted on a rack which is 5 12 feet above >>>>>> the >>>>>> roof surface. They will absorb reflected light on the backside, so I >>>>>> assume the cells will operate at a higher temp. But they are elevated >>>>>> enough to simulate a pole-mount, thus lowering operating cell temp. So >>>>>> what operating temp to use? If I use 25 C as the operating temp, the low >>>>>> voltage calc comes out to 301 vdc (inverter min is 300 using SMA >>>>>> US8000). If I use 15 C the calc is 308 vdc. This is for a 6 panel >>>>>> string. Unfortunately I really don¹t want to use 7 panel strings due to >>>>>> the layout. If I used a US7000 it would work since min vdc in is 250. >>>>>> However the inverters are part of a SunnyTower and I can¹t swap a 7000 >>>>>> for an 8000 without voiding the Tower UL listing. >>>>>> >>>>>> Kirk Herander >>>>>> >>>>>> VT Solar, LLC >>>>>> >>>>>> dba Vermont Solar Engineering >>>>>> >>>>>> NABCEP^TM Certified installer Charter Member >>>>>> >>>>>> NYSERDA-eligible Installer >>>>>> >>>>>> VT RE Incentive Program Partner >>>>>> >>>>>> *From:*re-wrenches-boun...@lists.re-wrenches.org >>>>>> [mailto:re-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of >>>>>> *b...@midnitesolar.com >>>>>> *Sent:* Wednesday, November 30, 2011 1:03 AM >>>>>> *To:* RE-wrenches >>>>>> *Subject:* Re: [RE-wrenches] calculating low string voltage >>>>>> >>>>>> >>>>>> >>>>>> If you really want to throw a monkey wrench into the mix, bring up >>>>>> partial shading... >>>>>> >>>>>> Or, maybe that's just not allowed in that debate ?? Just a thought. >>>>>> >>>>>> boB >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> On 11/29/2011 8:39 PM, Kent Osterberg wrote: >>>>>> >>>>>> Kirk, >>>>>> >>>>>> You've got some good feedback on this from Ray and Bill. I'll try to add >>>>>> a little more. Most module datasheets show a normal operating cell >>>>>> temperature, NOCT, value that's typically 47.5°C. That's 20°C ambient >>>>>> temperature, 800 W/sq m, and calm wind and nothing blocking the airflow >>>>>> on the back of the module. That 27.5°C temperature rise should be pretty >>>>>> close to the temperature rise that occurs for a pole-top mount. It's >>>>>> common to see people use 25°C for modules on a pole and 30°C or 35°C on >>>>>> a roof and there are data that support these "typical" values. With 1000 >>>>>> W/sq irradiance, the temperature rise can obviously be more too. Between >>>>>> the intensity of the sun, the direction of the sun, the color of the >>>>>> roof, the spacing off the roof, and the wind speed there is a lot that >>>>>> is different from one system to the next or even one day to the next. >>>>>> >>>>>> Most PV module spec sheets don't give you a temperature coefficient for >>>>>> Vmp. I've seen people use the the Voc coefficient, usually expressed as >>>>>> a percentage, for both Voc and Vmp. Big mistake. Data from NREL >>>>>> indicates as Bill said, the temperature coefficient for Vmp is higher >>>>>> than that the temperature coefficient for Voc. That's particularly true >>>>>> when the coefficient is expressed as a percentage per °C. Since there >>>>>> are very few manufacturer's that give both temperature coefficients, >>>>>> I'll use a value from an old Evergreen module for an example. The >>>>>> Evergreen ES-195 datasheet shows Voc = 30.5 volts with a coefficient of >>>>>> -0.34%/°C and Vmp = 27.1 volts with a coefficient of -0.47%/°C. Since >>>>>> one shouldn't add volts and percents, I'll put the temperature >>>>>> coefficients in volts/°C: Voc = 30.5 V - 0.10 V/°C and Vmp = 27.1 V - >>>>>> 0.13V/°C. So Vmp is moving faster than Voc, but not a lot faster. That's >>>>>> generically true for c-Si or poly-Si. >>>>>> >>>>>> Kent Osterberg >>>>>> >>>>>> Blue Mountain Solar, Inc. >>>>>> >>>>>> www.bluemountainsolar.com <http://www.bluemountainsolar.com> >>>>>> <http://www.bluemountainsolar.com> >>>>>> >>>>>> t: 541-568-4882 >>>>>> >>>>>> >>>>>> On 11/29/2011 11:48 AM, Kirk Herander wrote: >>>>>> >>>>>> I am in debate with a PE over calculation of low voltage of a series >>>>>> string on a hot day. He insists that an arbitrary high cell temp is >>>>>> factored in, not just ambient temperature. Could someone please give an >>>>>> accepted formula for this calculation? Thanks. I cannot find a clear >>>>>> reference to low voltage calculation on a hot day (but every reference >>>>>> material is clear on how to calculate high voltage on a cold day). >>>>>> >>>>>> Kirk Herander >>>>>> >>>>>> VT Solar, LLC >>>>>> >>>>>> dba Vermont Solar Engineering >>>>>> >>>>>> NABCEP^TM Certified installer Charter Member >>>>>> >>>>>> NYSERDA-eligible Installer >>>>>> >>>>>> VT RE Incentive Program Partner >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> _______________________________________________ >>>>>> >>>>>> List sponsored by Home Power magazine >>>>>> >>>>>> >>>>>> >>>>>> List Address:RE-wrenches@lists.re-wrenches.org >>>>>> <mailto: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-wrench >>>>>> es.org >>>>>> >>>>>> >>>>>> >>>>>> List rules& etiquette: >>>>>> >>>>>> www.re-wrenches.org/etiquette.htm >>>>>> <http://www.re-wrenches.org/etiquette.htm> >>>>>> <http://www.re-wrenches.org/etiquette.htm> >>>>>> >>>>>> >>>>>> >>>>>> Check out participant bios: >>>>>> >>>>>> www.members.re-wrenches.org <http://www.members.re-wrenches.org> >>>>>> <http://www.members.re-wrenches.org> >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> _______________________________________________ >>>>>> 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 >>>>>> <http://www.re-wrenches.org/etiquette.htm> >>>>>> >>>>>> Check out participant bios: >>>>>> www.members.re-wrenches.org <http://www.members.re-wrenches.org> >>>>>> >>>>>> >>>>> _______________________________________________ >>>>> 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 >>>>> <http://www.re-wrenches.org/etiquette.htm> >>>>> >>>>> Check out participant bios: >>>>> www.members.re-wrenches.org <http://www.members.re-wrenches.org> >>>>> >>>>> >>>>> >>>>> >>>>> >>>> >>>> _______________________________________________ >>>> 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 >>>> <http://www.re-wrenches.org/etiquette.htm> >>>> >>>> Check out participant bios: >>>> www.members.re-wrenches.org <http://www.members.re-wrenches.org> >>>> >>>> >>>> >>> >>> >>> >>> _______________________________________________ >>> 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 <http://www.re-wrenches.org/etiquette.htm> >>> >>> Check out participant bios: >>> www.members.re-wrenches.org <http://www.members.re-wrenches.org> >>> >>> >> >> >> >> _______________________________________________ >> 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 <http://www.re-wrenches.org/etiquette.htm> >> >> Check out participant bios: >> www.members.re-wrenches.org <http://www.members.re-wrenches.org> >> >> > > > _______________________________________________ > 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 > David Brearley, Senior Technical Editor SolarPro magazine NABCEP Certified PV Installer david.brear...@solarprofessional.com Direct: 541.261.6545 Fax: 541.512.0343 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