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Confused on voltage reading higher than sticker?

michaelcarmichael

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Joined
Apr 9, 2021
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Hey Solar Gang!

I'm a total newbie here and have been inspired by Will's videos to start putting together my own DIY solar system for my home.

I'm working with a tight budget, so I figure I could save some money by buying used solar panels on craigslist. I found a guy willing to sell 210w panels for $50ea., which seemed like a decent deal to me. I went to go test one of the panels and the voltage reading was higher than the sticker on the back, and the amp reading was lower. I've attached a photo of sticker.

My multimeter read 31.8volts & 5 amps...ultimately 159w, which is nearly 80% efficiency vs the 210w rating, which seems good I think.

Is there something wrong with the panel reading a lower amperage and higher voltage than the sticker, or do you think its a safe buy? Also do you think $50/panel is a good deal?

Thanks in advance for your insights!
 

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That's about right: The open circuit voltage on your sticker is over 33v. This will reduce when you actually hook something up to it.
So, these are nominally 24v panels, I assume.

Just curious - what were you running when you measured 5A? This would be the current actually passing through.
 
Voc = 33.68V
Vmp = 26.33V
Imp = 7.98A
Isc = 8.35A

"My multimeter read 31.8volts & 5 amps...ultimately 159w,"
At what condition of enviroment you made the measurement?
How did you measure the 31.8V? No load connected, right?
How did you measure the 5A?
 
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Conditions was just angling it toward the sun on sunny day...not sure if you mean something else?

Correct, no load connected for volt measurement.

I measured amps via my multimeter without load (based on YouTube video I watched). I'll admit, I am very unsure of what I'm doing...but attached is a screenshot circling the settings I had with my multimeter.

Also, correction on my efficiency math from earlier post...159w is 75.7% of 210w rating, not 80%...assuming I'm measuring correctly.

Thanks guys for your help!Screenshot_20210409-164752~3.png
 
Vmp * Imp = Panel Wattage rating.
26.33V * 7.98A = 210W
You calculation was based on open Voltage reading, not with load so that 159W is not valid.
At this point I do not think you have anything to worry about this used panel. $50 is a good price for used 210W panel.
The spec pirnted on the back panel is done in laboratory setup condition and using calibrated equipment.
 
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