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solar cell defects?

Hi asp, sec!

I bought 300 "Class/Grade A" solar cells [1]. Just when I wanted to resell some of them I discovered that most of them (all that I checked) have a few (about 2-6) complete or partial gaps in the finger traces that pick up the electricity and forward it to the bus bars. There are also marks on the edge that look like overheated spots:

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Many of the gaps appear in sequential cells in the same position, so it seems it's a fabrication mask error, not a shipping defect.

Are these significant defects? Do they reduce performance or life time? Would you care about them?

I have a bunch of Grade B polycrystalline cells with no such defects.

Thanks, Bernhard

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Reply to
Bernhard Kuemel
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Did you buy chinese solar cells off ebay?

are you surprised at what you got?

Reply to
Cydrome Leader

Yes.

At first I was worried, but now I think, maybe they produce their stated power with these defects. It's typically no more than one open in a finger, so each part is connected to a bus bar. Cost optimized.

Reply to
Bernhard Kuemel

These low efficiency mono-cells can't be grade A, or they are labeled 3 years ago. And I think there is a little error on the label: The diagonal can't be 195mm (should be 200mm I think), or 17.75% efficiency and 4.24W will not agree. Anyway it's really cheap and worth the price.

As to what you concerned, you have guessed quite right. The broken finger bars come from electrode printing error (mostly attributed to bad mask) , and the gray marks on the edge is actually not error, but normal behavior of coating with some equipments. Since the label says "coating: CT", I think it's Centrotherm, whose equipments are used largely, and do leave such spots on cells. Strange though, such information is seldom printed on labels.

Since these defects are formed before I-V testing, you don't need to care about them, as long as the efficiency is labeled correctly. And they don't reduce life time.

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Regards, 
Lu Wei 
PGP key ID: 0x92CCE1EA
Reply to
Lu Wei

Those conductor breaks look harmless because there are no islands. The edge colors are normal.

A problem with crappy solar cells is internal leakage. They'll perform to spec in full direct sunlight but you'll get zero volts indoors or in the shade. There's a lot of IR indoor near lamps and a lot of UV outdoors in the shade so a decent solar cell still has some use without direct light. You can always do a side-by-side comparison with a known quality cell.

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I will not see posts from Google because I must filter them as spam
Reply to
Kevin McMurtrie

They might be 3+ years old, I don't know. They are said to be surplus of some people making solar panels.

Interestingly I got cells with 195 mm and 200 mm diagonal, both 156*156 mm square. It's only a little difference at the corners.

Bernhard

Reply to
Bernhard Kuemel

My cells have 0.46 V and 39 mA inside in the shade. I put them in a stainless steel pan as backside contact and touched the middle bus bar with a multimeter probe. My desk is next to the window, it's a bright day outside, no direct sun hitting my window, just some diffuse reflections.

Bernhard

Reply to
Bernhard Kuemel

17.75%, 156*156 and 195 diagonal will give 4.197W. The difference is small but could not be mis-labeled. Maybe the package is not original. 
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Regards, 
Lu Wei 
PGP key ID: 0x92CCE1EA
Reply to
Lu Wei

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