Solar Panels not generating enough power

[Hedges]

Blemished SanTan 250W (SSG) Solar Panel | SanTan Solar

www.santansolar.com

"The panels still output approx. 75% of the listed specifications.”

Blemished Trina 245W Solar Panel | SanTan Solar

www.santansolar.com

"We tested some panels and they were producing about 80% of stated power."

 

[740GLE]

I have 2 strings of the used Trina 240w panels. Each string goes into a separate controller. I got an Elejoy meter that runs MPPT and reports watts. 7 of my used panels were all very close at:
Watts: 150
Inp: 7.1
UMP 21.5

One panel was:
Watts: 75
Inp: 0.03
UMP 25.15

While testing I used contact cleaner and carburetor brushes on the connectors. It didn't make a difference. My panels are mounted on a movable platform so I could figure out a location that would work. The panels are at the correct angle and at solar south. Prior to commissioning I gave them a good cleaning, this made a big difference.

I'm assuming the reason the string with the underperforming panel wasn't dead is because the voltage on the bad panel is okay?

Do you use that type of meter with a control panel to verify haze or heat isn’t messing up your readings?

Doesn’t take much for a panel to read low outputs.

 

[Rafagus]

Do you use that type of meter with a control panel to verify haze or heat isn’t messing up your readings?

Doesn’t take much for a panel to read low outputs.

No my meter doesn't do that. I'm just looking at the consistency of one panel to the next. With the humidity here, South Louisiana, it's a rare day in the summer that there is no haze. I'm okay with the 60% of rated, for what little I paid it's a good deal and will be buying more. Also I'm on the ground and have more room than money

I restored my, 1880s, house with solar in mind. I'm 100% Mini Split and can run my house on peanuts. When I get my array(s) to 50% of my controllers input max I'll be making more energy than I can use. Between having plenty of room for the ground arrays and low needs, buying used panels makes sense for me.