Hey Brian, Following up on both sets of questions:
Can you attach the spec sheet? Does it show curves at different irradiances? — ATTACHED What was the time of day (or was it just cloudy?). — ~11:00am How are you measuring the cell temp? — Fluke Temp gun (new battery) The string voltages were +/- 1.5% of adjacent Meter — Hioki CM4374 (calibrated recently) Testing a single module, while ideal, is not practical unless we run into issues. I should have the ~480 strings worth of measured data back later today. > On Nov 3, 2020, at 2:52 PM, Brian Mehalic <[email protected]> wrote: > > Hey Jason, IEC 62446-1 allows for: > > Testing Voc of a single module and using that to calc the target string > voltage > and > "For systems with multiple identical strings and where there is stable > irradiance conditions, voltages between strings can be compared" > > Regardless, it would be interesting to have a test on a single mod (well some > number of single mods). > > What meter are you using, and has it been calibrated recently? > > > 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 <http://www.solarenergy.org/> > > SEI Professional Services > http://www.seisolarpros.com <http://www.seisolarpros.com/> > > > > On Tue, Nov 3, 2020 at 10:32 AM Brian Mehalic <[email protected] > <mailto:[email protected]>> wrote: > A few more questions: > > Can you attach the spec sheet? Does it show curves at different irradiances? > > What was the time of day (or was it just cloudy?). > > How are you measuring the cell temp? > > Brian > > > On Nov 3, 2020, at 8:50 AM, Jason Kechijian <[email protected] > > <mailto:[email protected]>> wrote: > > 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 <[email protected] <mailto:[email protected]>> > >> To: RE-wrenches <[email protected] > >> <mailto:[email protected]>> > >> Subject: Re: [RE-wrenches] Bi-facial Open Circuit voltage testing > >> Message-ID: <[email protected] > >> <mailto:[email protected]>> > >> 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 <[email protected] > >> <mailto:[email protected]>> > >> To: "RE-wrenches" <[email protected] > >> <mailto:[email protected]>> > >> Subject: Re: [RE-wrenches] Bi-facial Open Circuit voltage testing > >> Message-ID: <[email protected] > >> <mailto:[email protected]>> > >> 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/ <http://members.sti.net/offgridsolar/> > >> e-mail [email protected] <mailto:[email protected]> > >> text 209 813 0060 > >> > >> > >> ------------------------------ > >> > >> Message: 4 > >> Date: Mon, 2 Nov 2020 09:53:43 -0700 > >> From: Brian Mehalic <[email protected] <mailto:[email protected]>> > >> To: RE-wrenches <[email protected] > >> <mailto:[email protected]>> > >> Subject: Re: [RE-wrenches] Bi-facial Open Circuit voltage testing > >> Message-ID: > >> <capkgs9tz6yehzweoardp0mvamhuxmfhcluoprowetxynew0...@mail.gmail.com > >> <mailto: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 <http://www.solarenergy.org/> > >> > >> SEI Professional Services > >> http://www.seisolarpros.com <http://www.seisolarpros.com/> > >> > >> > >> > >>> On Mon, Nov 2, 2020 at 8:55 AM Jay <[email protected] > >>> <mailto:[email protected]>> 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 <[email protected] > >>>> <mailto:[email protected]>> 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. 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