I purchased used solar panels and have a question about the output...

[Eric in TN]

Hi all, I ended up getting the exact same setup that Will Prowse did a video on, the new (2 of them) EG4 6500 EX 48 and (6) - EG4 LiFepower 4 batteries. I purchased 30 used solar panels from GreenManSolar online. They advertised on FaceBook that the panels output would be 95% of when they were new. Original Open Circuit Voltage was 37.6, the panels I received averaged out to 35.16v (93.5% of new). The original amperage was 8.27 and mine averaged out to 7.43 (89.8%). My question is, are these lower numbers going to have much of an effect on my system's performance? The company wants to make me happy and I don't want to take advantage of them but I do want to make sure I am getting good results after spending all this money on the system. This is my first solar build and your feedback is very much appreciated. Thank you, Eric

 

[sunshine_eggo]

Did you test those in accordance with STC conditions to confirm the ratings you're quoting?

1000W/m^2 insolation?
25°C cell temperature?

Given that STC conditions only exist in a lab, I doubt it.

Many panels give a NOCT rating or some other label that don't remember. These ratings represent more typical performance in real-world conditions where insolation is reduced (800W/m^2) and cell temperatures are HOT (depends on manufacturer, but typically 40-50°C).

 

[Eric in TN]

Did you test those in accordance with STC conditions to confirm the ratings you're quoting?

1000W/m^2 insolation?
25°C cell temperature?

Given that STC conditions only exist in a lab, I doubt it.

Many panels give a NOCT rating or some other label that don't remember. These ratings represent more typical performance in real-world conditions where insolation is reduced (800W/m^2) and cell temperatures are HOT (depends on manufacturer, but typically 40-50°C).

Being new to this, I know I have a lot to learn. I picked a cloudless day with the sun directly overhead to test the panels. I only had each panel in the sun long enough to take the readings as I had read that the panel's efficiency goes down as it gets hotter. It was in the mid 80s on the day I tested. I figured that was as close to perfect conditions as I would be able to get. Are the numbers I was getting anything to be concerned about? Thanks

 

[Kornbread]

Curious, what was your method for testing them?

 

[Eric in TN]

Curious, what was your method for testing them?

I used a multi-meter for DC amps and DC voltage. I put the probes in the connectors and took the initial reading before the numbers dropped. I noticed that each time I retested for voltage, the reading would go down.

 

[Kornbread]

First time I tried to measure dc amps with a multimeter, the plugs hisssssed at me when removing the multimeter probes. I didn't have any luck trying to deal with GreenManSolar but have heard others with good reviews and IMO, if the panels are seven'ish or so years old, I'd consider 80% about normal. I'm the kind of person that if someone warranties 95%, it better do 95%, but it's dang near impossible to test them under 'lab' conditions.

 

[Eric in TN]

I got some of the hissing action too if I didn't make the connection fast enough. Thanks for your your opinion on the percentages. So far I am happy with GreenManSolar's customer service. Kendra is very customer service friendly.

 

[OffGridIdaho]

Coming from a photography background and shooting the grand canyon I can tell you that a clear sunny day is anything but!
You need to find out the particulate matter in the sky that day and also the moisture content. Those 2 things can drop solar by 25% or more.
A clear day isnt always a clear day.

 

[Vigo]

^Thought provoking!

Anyway, wouldn't the main question here be, did you size your solar array with so little headroom that losing 10% off the solar already ruins your plan?! When i bought my used panels, i bought about twice what i thought i 'needed' and then thought about buying a few more just in case any showed up broken. I think the low price of used panels in many cases should be incorporated as a cheaper way to build in some headroom, rather than looking at it as 'doing the absolute bare minimum just got cheaper!' I have 44 similarly-spec'ed panels in operation and live comfortably off grid in a small home with them. 30 might be plenty depending on the use case.

I think if they are doing ~90% of their rating you should definitely just run it. I DO think claiming 95% on used panels is BS unless they're very new. I would just assume 80% for anything used and plan accordingly, but i'd rather be pessimistic on the front end and be happy with what i get, than deal with a slowly unfolding novel of disappointment from being optimistic. That's a personality thing, so YMMV.