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
