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solar cell defects?

Discussion in 'Photovoltaics' started by Bernhard Kuemel, Jul 17, 2013.

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  1. 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:

    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

  2. Did you buy chinese solar cells off ebay?

    are you surprised at what you got?
  3. 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.
  4. Lu Wei

    Lu Wei Guest

    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.
  5. 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.
  6. 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.

  7. 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.

  8. Lu Wei

    Lu Wei Guest

    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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