Hey Jay and Brian, System: 2p SAT Mods/String: 27
Measurements taken on average of CB Ambient: ~23ºC Module: 21.4ºC Wind: moderate Irradiance: 500W/m2 Expected Voc: 1,320.37 Testing based on IEC 62446 Measured Voc on a range of 9 string combiner: 1251 - 1271. 1251 being the only string in the CB at less than 5% of expected, which I am sure the wind had some effects. All voltages in the CB were +/- 1.5% of the adjacent. I’ll share more results as the come in from the field. The questions: Which of the two Vocs should we use? The average of the two? Since we are not taking the BOM temp measurements from a back sheet, but rather a cell. What does the thermal effect of glass play on the temperature reading vs. the back sheet. (May be wording this wrong, but I think y’all get the point) I have searched the inter webs and not found much guidance/support in particular to this query. Jason Kechijian > > > Hey wrenches, > > Does anyone have any guidance to which values to use when testing open > circuit voltage on bi-facial modules, considering you take the temperature > reading from the cell vs. the back sheet? Also, what would be the correct > module Voc to use since there are values for both the front and back? > > 405W Module: Front/Back > Pmpp: 405 / 285 > Vmpp: 40.89 / 41.10 > Impp: 9.91 / 6.94 > Voc: 48.42 / 46.99 > Isc: 10.38 / 7.28 > Module efficiency: 19.7% / 13.9% > Temp coefficient Pmpp: -0.3528%/?C > Temp coefficient Isc: +0.0400%/?C > Temp coefficient Voc: -0.2769%/?C > Nominal: 44+/-2?C > > I was using the front Voc and Voc temp coefficient, but I am getting some > results which are not in line with the 5% of expected. > > Jason D. Kechijian, LEED AP > NABCEP Certified PV Installation Professional? > > > > > > ------------------------------ > > Message: 2 > Date: Mon, 2 Nov 2020 08:25:20 -0700 > From: Jay <jay.pe...@gmail.com> > To: RE-wrenches <re-wrenches@lists.re-wrenches.org> > Subject: Re: [RE-wrenches] Bi-facial Open Circuit voltage testing > Message-ID: <50543918-a062-456f-ac6d-6970c793f...@gmail.com> > Content-Type: text/plain; charset=utf-8 > > Hi Jason, > > What are you seeing in terms of measurements? > > Temp air/module > Voc > Irradiance > Etc > > Jay > Peltz power > > > Message: 3 > Date: Mon, 02 Nov 2020 08:41:21 -0800 > From: Dave Angelini Offgrid Solar <offgridso...@sti.net> > To: "RE-wrenches" <re-wrenches@lists.re-wrenches.org> > Subject: Re: [RE-wrenches] Bi-facial Open Circuit voltage testing > Message-ID: <4af9d868a899895ed1fd8ad15ba0ff2e@127.0.0.1> > Content-Type: text/plain; charset=UTF-8 > > I am curious why you care? Is it close to maxing out cold weather Voc for > one more panel in the string? If so I would be conservative and use one > less panel. > > I have an old Sanyo Bi Array and it pretty much has never gone outside the > cold weather Voc that is logged by the controller. The 600v mppt just > cranks out the power when the snow is off the array. It does pretty well > also when the snow is on it. > > Just curious what you are doing? Testing used panels to make sure they are > good? If so I would line them all up exactly the same and have a second set > of eyes to record it all. > > > Dave Angelini Offgrid Solar > "we go where powerlines don't" > http://members.sti.net/offgridsolar/ > e-mail offgridso...@sti.net > text 209 813 0060 > > > ------------------------------ > > Message: 4 > Date: Mon, 2 Nov 2020 09:53:43 -0700 > From: Brian Mehalic <br...@solarenergy.org> > To: RE-wrenches <re-wrenches@lists.re-wrenches.org> > Subject: Re: [RE-wrenches] Bi-facial Open Circuit voltage testing > Message-ID: > <capkgs9tz6yehzweoardp0mvamhuxmfhcluoprowetxynew0...@mail.gmail.com> > Content-Type: text/plain; charset="utf-8" > > I second Jay's request for some numbers, I'm curious about this not having > participated directly in any bifacial projects yet. The difference in Voc > and Vmp ratios is interesting. > > Brian Mehalic > NABCEP Certified Solar PV Installation Professional? R031508-59 > National Electrical Code? CMP-4 Member > (520) 204-6639 > > Solar Energy International > http://www.solarenergy.org > > SEI Professional Services > http://www.seisolarpros.com > > > > On Mon, Nov 2, 2020 at 8:55 AM Jay <jay.pe...@gmail.com> wrote: > >> Hi Jason, >> >> What are you seeing in terms of measurements? >> >> Temp air/module >> Voc >> Irradiance >> Etc >> >> Jay >> Peltz power >> >> >>> On Nov 2, 2020, at 8:18 AM, Jason Kechijian <sol...@me.com> wrote: >>> >>> ?Hey wrenches, >>> >>> Does anyone have any guidance to which values to use when testing open >> circuit voltage on bi-facial modules, considering you take the temperature >> reading from the cell vs. the back sheet? Also, what would be the correct >> module Voc to use since there are values for both the front and back? >>> >>> 405W Module: Front/Back >>> Pmpp: 405 / 285 >>> Vmpp: 40.89 / 41.10 >>> Impp: 9.91 / 6.94 >>> Voc: 48.42 / 46.99 >>> Isc: 10.38 / 7.28 >>> Module efficiency: 19.7% / 13.9% >>> Temp coefficient Pmpp: -0.3528%/?C >>> Temp coefficient Isc: +0.0400%/?C >>> Temp coefficient Voc: -0.2769%/?C >>> Nominal: 44+/-2?C >>> >>> I was using the front Voc and Voc temp coefficient, but I am getting >> some results which are not in line with the 5% of expected. >>> >>> Jason D. Kechijian, LEED AP >>> NABCEP Certified PV Installation Professional? >>> >>> >>> >>> _______________________________________________ >>> List sponsored by Redwood Alliance >>> >>> List Address: RE-wrenches@lists.re-wrenches.org >>> >>> Change listserver email address & settings: >>> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org >>> >>> There are two list archives for searching. 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