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1. Originally Posted by greenHouse
A solar panel is a "constant voltage" current source. string / panel up to its voltage.
Beg your pardon, solar panels are constant current sources.

2. Originally Posted by Sunking
Beg your pardon, solar panels are constant current sources.
Excuse me? Constant =when=?

The current is constant from Vmpp to 0, more or less. In the voltage range from Voc to Vmpp, the current isn't constant (it goes from 0 to Impp). From this, you can deduce how to add mismatched panels to an array (the topic ...) in a way that minimizes losses.

3. Originally Posted by greenHouse
The current is constant from Vmpp to 0, more or less. In the voltage range from Voc to Vmpp, the current isn't constant (it goes from 0 to Impp). From this, you can deduce how to add mismatched panels to an array (the topic ...) in a way that minimizes losses.
Yep and that is why pros should be doing that work. It is beyond DIY knowledge in most cases. As for me I like to KISS.

4. Originally Posted by Sunking
Yep and that is why pros should be doing that work. It is beyond DIY knowledge in most cases. As for me I like to KISS.
The rules are simple enough that if explained properly, even a 6th grader can do the math. It's far from difficult, and "replace them all" is far from the only reasonable course of action.

5. Originally Posted by greenHouse
"replace them all" is far from the only reasonable course of action.
Who said that? You did right? You forget most the people who come here are DIY and have no electrical knowledge what so ever and are not going to take the time to learn the math.

If you mix panels there will be consequences with some power losses ranging from minor to severe. In a battery system there are effective means to mix panels by segregating panels into separate groups and running them on a dedicated charge controller combing there output to a common battery. All that can be avoided by purchasing panels from companies like BP, Kyocera, and Sanyo who have been around a long time and will be around tomorrow to supply you with the same model panel for replacement and future expansions. That is the smart money approach.

6. Originally Posted by Sunking
Who said that? You did right? You forget most the people who come here are DIY and have no electrical knowledge what so ever and are not going to take the time to learn the math.

"You would be better off selling them on ebay and starting over with quality panels."

7. I guess I'll just step in and end this nonsense. The job was a pro bono job using what the customer had laying around. I chose not to use some of the mismatched panels b/c they were not UL listed. I arranged the panels in a single string. The values I was reading after the install were comparable to the values I had calculated originally (current was the limiting factor in this case). I chose a single string b/c I had to match the inverter tracking voltage. The panels were all the same nominal voltage just different power outputs. I ended up losing ~120 W power with the mismatch. It didn't matter to the customer since they had received the equipment for free from my company. The job is currently producing ~2000 W AC power and everyone is happy. I declare this thread and internet pissing contest over!

8. Originally Posted by SolarGuyTX
I guess I'll just step in and end this nonsense. I chose not to use some of the mismatched panels b/c they were not UL listed. I declare this thread and internet pissing contest over!
Good job and I agree. Bye!

9. Originally Posted by Sunking
You forget most the people who come here are DIY and have no electrical knowledge what so ever and are not going to take the time to learn the math.
That's one heck of a statement.
Simply because one may be a DIYer I don't see why that would make you conclude that they would not take a small amount of time to learn simple math or electrical concepts.
If they weren't willing to learn a small amount then chances are they would not be here.
If someone does not wish to learn anything then they simply will not become a DIYer.

10. Sparky

You forget that a lot of people only need to or should only need to know the basics 1st and build on from there.Throwing mathematical formula at someone just starting out is bound to confuse some and chase a lot of people.Better to build on to a knowledge base that is stable. i.e. Crawl before you walk.