Renewable Energy Questions/Discussion > Solar (heating or electric)

Intro and questions, if I may

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ksouers:
Thanks Chris. I won't worry about it any further then.

rossw: Thank you for relating your experience. I'm sure glad you weren't hurt! I know I would have had a dirty diaper at the least! Also glad everything worked out well with the vendor. I'm always afraid dealing with Chinese vendors. I've only dealt directly with a Chinese vendor once and all was well. Usually a US vendor will make good on a Chinese product even if the manufacturer won't. But then I only buy from established businesses, ebay scares me. I much prefer doing business where the owner is right there on site. It may cost a little more but I know where to go when there is a problem, no email tag with someone halfway round the world.

I will add diodes. Must they be schottky? I know they are low-loss, but that's about all I know. My thinking was the cells already have diodes on them to prevent loss and back current for shadowing and dead cells, therefore diodes weren't needed on the pig tails.

rossw:

--- Quote from: ksouers on February 01, 2012, 07:18:11 pm ---rossw: Thank you for relating your experience. I'm sure glad you weren't hurt!

--- End quote ---

I was doing it all "safely". There was never any risk to me, which is more than be said for the panels.
I'd honestly never heard of or thought about the problem. I've had diodes avalance before with DV/DT so I SHOULD have considered it. But I just didn't. More fool me.


--- Quote ---I'm always afraid dealing with Chinese vendors.

--- End quote ---

I purchased quite a bit from this guy, and was in regular contact with him by skype.


--- Quote ---I will add diodes. Must they be schottky? I know they are low-loss, but that's about all I know. My thinking was the cells already have diodes on them to prevent loss and back current for shadowing and dead cells, therefore diodes weren't needed on the pig tails.

--- End quote ---

Do the math.
A typical schottky diode with 8A through it will drop around 0.5V Power = V*A = 4W. Typical junction to heatsink and heatsink to air thermal resistance with a modest heatsink area but without forced air cooling is probably around  10 degC/W. So with ambient temperature of say 40 degrees, add another (4*10) = 80 deg C. Not so bad.

A typical rectifier diode will go close to 1V, so power = 8W, and now we're up to 120 deg C.

*PER DIODE*.

Watt:

--- Quote from: rossw on February 01, 2012, 07:12:57 pm ---
--- Quote from: Watt on February 01, 2012, 07:02:45 pm ---Wow, thanks for sharing this post with us Ross.  That's an eye opener for sure.  So, did you get to keep the replaced set on top of the replacements?

--- End quote ---

No, I only asked for (and received) the diodes.
There was no damage (that I could ascertain) to the rest of the modules.
Since the man in China was so eager to help out, and sent me 15 diodes (I needed 12), without any hassles, and wouldn't take any money, AND sent them international overnight courier, there's no way I was going to try to screw him for more panels.

I fixed them with his parts and my labour, and was happy to come to such a resolution so quickly and with so little out-of-pocket expense.

--- End quote ---

Sorry Ross, I should have realized they may not want to deliver whole panels next day for free and never thought about repairing them even though you said they were all fixed.  OOPS, taking foot out of mouth now...

ksouers:
Thanks Ross. I love learning this stuff.
I can dwiddle bits with the best of them (I'm also a grumpy Unix admin, AIX flavored) but electronics makes my head hurt.

Kevin

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