Renogy 100W panels, identical model number, different voltages

[JWLV]

Currently I have 2 Renogy 100W panels among another brands. The Renogy is hooked up to its own string with a separate MPPT controller. I was planning to get 2 more of the identical Renogy panels so that I could have 400w on one string. All 4 panels would be connected in series. There's a guy locally selling 2 Renogy 100W panels and I was just about to buy and I noticed the voltages are different.

Picture 1: My current panels.
Renogy RNG-100D-SS. VoC is 20.0V, Vmp is 16.0V, Imp is 6.25A, Isc is 6.45A.

Picture 2: The panels I was going to buy.
Renogy RNG-100D-SS. VoC is 21.6V, Vmp is 17.9V, Imp is 5.72A, Isc is 6.24A.

What's with Renogy? These panels have the exact same model number. Yet the specs differ by as much as 10%.

 

[MisterSandals]

Yet the specs differ by as much as 10%.

You would probably never know the difference unless measuring VERY carefully.

Is there a reason in particular you are set on using a lot of tiny panels?

 

[timselectric]

Those are close enough for series. I assume you want the small panels for portability.

 

[Symbioquine]

Under perfect conditions:

All in series = 67.8v@5.72A = 387.8 watts = 3.05% loss
All in parallel = 16.0v@23.94A = 383.0 watts = 4.25% loss

In mixed 2P2S = 32v@6.25A + 35.8v@5.72 = 32v@5.72A = 383 watts = 4.25% loss

Probably not enough losses to stress about.

You could put them on separate charge controllers, but that money would probably be better spent on additional/better panels if you have the space.

If you were going for East/West facing panels anyway (for other reasons, like space constraints), you could do 2P2S for the two strings and potentially take advantage of the bypass diodes to get the full rated amps from East OR West at a time (not both - so total losses over a day would still be higher than above).

Ref: https://www.explorist.life/using-mismatched-solar-panel-sizes/

 

[MichaelK]

My recommendation would be to forget about Renogy completely, and try buying your panels locally, instead of mail-order. Shop on Craigslist with local pickup and you are likely to get 4W of solar for the price of 1W of Renogy solar.

 

[sunshine]

The panels will need to get tested after x number of batches or any significant manufacturing change and the extra weight of the bottom panel shows a significant change.
The extra weight of the bottom one probably means it is the older one. You can deduce whatever you like from Renogy dropping TUV as a testing lab if this is the case.

 

[JWLV]

Thanks for the calculations @Symbioquine

The reason I'm still using these small 100W panels is because I plan to mount these panels on top of my covered patio. The covered patio probably can't hold a lot of weight, so it should be fine if I spaced these smaller panels out and distribute them evenly. Up on the patio, these panels will not get any shade from the nearby trees. My larger 300W panels are on the ground and they do get some shade at certain times of day.

@sunshine You're right! I didn't even notice the weight difference between the panels. 2.2 pounds difference for a small panel is quite significant!

 

[evilroy]

I recently checked my 10 year old 100 watters with new and found the same thing....I guess Older is better!