Testing Solar Panels On Suboptimal Conditions/Cloudy Day


New Member
Was looking for some used panels for my RV and found some used Trina 250w panels on FB marketplace for a good price. They are 10 years old so I want to make sure they are still producing before I purchase them. I was going to bring my multimeter along and test them but its going to be cloudy the next week. Obviously the output will be lower but is there a certain range/percentage of output where I can safely say the panels are still performing as they should? Any advice appreciated. Thanks!

link to the model: https://www.solarelectricsupply.com/trinasolar-tsm-250pa05-solar-panels

Peak Power Watts-PMaX(Wp)250
PTC Rating227.5
Power Output Tolerance-PMaX(%)0/+3
Maximum Power Voltage-VMP(V)30.3
Maximum Power Current-iMPP(a)8.27
Open Circuit Voltage-VOC(V)37.6
Short Circuit Current-iSC(a)8.85
Module Efficiency ηm (%)15.3


Solar Honey Badger
Panel specification are for 1000W/m^2 conditions. Unless you first measure the solar irradiance, nothing meaningful can be gleaned.

Your only realistic hope is to test during a period of full sun with the panel oriented as close to perpendicular as possible.
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