An Isc test will not find a series resistance problem. You have to put a real load on the panel or string to find this type of problem.
David On Oct 6, 2015, at 4:58 AM, Chris Mason wrote: > If you use the PV150 tester, it will do this test, giving you the Isc for > each panel you test. The Isc should be the same for all panels given the same > irradiance. It does all the other tests at the same time, and you can record > the results to an Excel format report, including the irradiance at the moment > of the test. > As you can string test, which will identify any strings with bad panels, I > think this should be a minimum for any commissioning report. > > > On Tue, Oct 6, 2015 at 12:57 AM, David Coale <da...@evcl.com> wrote: > Hi Wrenchers, > > I have found on the older panels, especially the AstroPower line, the > problems tend to be bad solder joints. This shows up as a series resistance. > As such, the open circuit voltage and short circuit current will read good. > It is not until you put an external load on the panel that you will see any > problems. If you want to draw out a simple circuit with a voltage source, a > current source and a series resister, you will see this quite clearly. > > On these older systems I am just looking for the few bad panels to be > replaced or fixed (more info on fixing if requested). I am not looking to > find the MPP output or the corrected performance of the panel with all the > relevant parameters accounted for. A very easy way to do this is to just > have one or two 50 watt 12 volt halogen bulbs as a load and measure voltage > and current across each pane with this load. I try one bulb and then two > bulbs in series and use whatever set up gives me the highest wattage reading > and then use this load for the rest of the testing. Bad panels (AstroPower) > tend to be 1/2 the output relative to the good panels, or almost no output at > all depending on where the bad solder joint is. > > If you have a bunch of panels you can take down the measurements and then > sort through them and get the best panels for your system (I have an excess > of panels at this point). It is helpful to have an irradiance meter to make > sure you are testing all the panels with about the same input for comparison. > The panels of course have to have about the same angle to the sun and > similar temp to make the comparison valid. I usually have the panels in the > shade and then pull them out for testing so that the temp is all about the > same. They can also be tested in place if you can access the leads for > testing. > > I have built a tester with several bulbs and a toggle switch that will let > you easily switch between Voc, Isc and with a load using two meters, one for > voltage and one for current to make the readings at the same time. No fancy > testers required for just finding the few bad panels. > > David > > On Oct 5, 2015, at 7:46 AM, Starlight Solar Power Systems wrote: > > > Bill, > > > > In the shop I have two electronic loads that I use nearly every day with > > batteries and PV modules. One is a programmable 150W, 360V that can be set > > for constant power, current or voltage (like this: > > http://www.amazon.com/Programmable-Electronic-Load-360VDC-CSI3710A/dp/B00D7QGSV4). > > It’s small enough to take to the field. The other is a 2kW model that I > > use for battery load and discharge testing. It’s too big to move. > > > > I also use the Daystar DS-05A (seen here: > > http://www.amazon.com/Daystar-DS-05A-Solar-Digital-Meter/dp/B00YVTXZJ4/ref=sr_1_fkmr0_1?s=electronics&ie=UTF8&qid=1444055204&sr=8-1-fkmr0&keywords=Daystar+PV+irradiancePV) > > irradiance meter to calculate power by holding it in the same plane as the > > module to determine actual irradiance striking the surface. > > > > Another tool I use is a simple instant read, non contact infrared > > thermometer to check the cell temperature under test. > > > > With these tools and a little information, I can measure instant power and > > calculate module degradation. Others have suggested higher cost tools but > > these low cost tools have been reliable for many years. > > > > Larry > > > > On Oct 4, 2015, at 7:56 PM, frenergy <frene...@psln.com> wrote: > > > > Wrenches, > > > > As time passeth, we're bumping more into older PVs/arrays that have > > questionable outputs. After minimizing the variables (dust, temps, sun > > angle, wiring, expected deterioration with age, etc) and still coming up > > with low numbers. Testing individual PVs' Voc and Isc don't seem to tell > > the whole story as they often look good. > > > > Would not a definitive test be to wire a suspect PV to an inexpensive > > mppt CC (oxymoron?) and then to an orphaned battery. The battery would > > have to have a mondo (surplus) rheostat paralleled to it to maintain a > > steady voltage during the test. With appropriate metering in place, you > > would then have Vmmp and Immp as the rheostat is tweaked to hold a steady > > batt voltage and the CC finds the knee. > > > > Help me here. I know its a little spendy to cobble up but the value > > of nailing an offender might be worth it. Am I missing something? Is it > > common for inverters to fall off in output gradually? > > > > Bill > > Feather River Solar Electric > > > > _______________________________________________ > > > > _______________________________________________ > > 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 > > > > List-Archive: > > http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html > > > > List rules & etiquette: > > www.re-wrenches.org/etiquette.htm > > > > Check out or update participant bios: > > www.members.re-wrenches.org > > > > _______________________________________________ > 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 > > List-Archive: > http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out or update participant bios: > www.members.re-wrenches.org > > > > > -- > Chris Mason > NABCEP Certified Solar PV Installer™ > Solar Design Engineer > Generac Generators Industrial technician > > www.cometsolar.com > 264.235.5670 > 869.662.5670 > Skype: netconcepts > _______________________________________________ > 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 > > List-Archive: > http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out or update participant bios: > www.members.re-wrenches.org >
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