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Why are solar panels full tabbed?

Discussion in 'General Electronics Discussion' started by Mongrel Shark, Jun 5, 2013.

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  1. Mongrel Shark

    Mongrel Shark

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    Jun 6, 2012
    So I just got a few stacks of some of ebays cheapest and nastiest silicon solar wafers out of my mailbox. Every tabbing guide I have seen says you have to run tabbing wire the full length of the panel. Yet a quick poke with multimeter probes seems to indicate otherwise.
    I cant seem to find any reason why the panels are full tabbed? The first thing that comes to mind is heat from amps and thin wire, but its short not thin. So the only other thing I can think of, is that the strips on the panel get hotter without extra conductivity? So thats a good reason to full tab the front, but why the back?


    Needless to say I will be doing a test with a few cells with really short tabbing, and a few fully tabbed. To see if I can find any difference in performance. Just curious what I should be looking at. Things I was going to monitor was volts, amps, and watts obviously. As well as temperature averaged across panel, and if there is a different temp near the tabbing stripes, with and without tabbing wire.


    Also, one type of panel I got has three strips for tabbing. each one has 0.5v Can I put them in series, and get 1.5v from a single cell? (Soldering iron is hot, I guess I'm about to find out :D)

    [​IMG]

    Here is a picture of some of the cells. I got 36 of the big ones, and 80 of the little ones. The small ones are for powering portable devices I plan on making. Total cost was $46 Australian. Including postage. I should get approx 70w from the big ones (155x80mm) and 20w from the small ones (55x20mm) They are polycrystalline B grades. I'll probably get Monocrystaline next, Just wanted some cheap ones to learn with. As I'll probably kill a few experimenting.
     

    Attached Files:

  2. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    The conductivity of the tabs is much higher than the silicon's conductivity. By covering more of the panel with tabs, the impedance and hence the losses are reduced. This increases the efficiency of collecting the electrons from the active area.

    However, this comes at the cost of reduced active area (no conversion happens under the opaque tabs). So the design and placement of the tabs is a compromise between conversion efficiency and collection efficiency. The y should be well balanced.
     
  3. Mongrel Shark

    Mongrel Shark

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    18
    Jun 6, 2012
    I just checked the resistance between the strips. Under 1 ohm. I guess I wont be putting one cell in series with itself.:(
     
  4. Mongrel Shark

    Mongrel Shark

    260
    18
    Jun 6, 2012
    So if I'm going to put cells in series, and have minimal amps flowing across them, I can have less tabbing, and if I put them in parallel for amps, I want more tabbing as the amps across each panel increases.

    To work out how much I need, I could start out with a bit, and add more until amps on a sunny summer day is not going up with more wire.

    As the panels have about 0.8-0.9 ohms from corner to corner, Lots of amps across lots of panels in series (Like resistors in series I'm guessing, will sum the resistance from each panel) will start heating the panel, at some point this will reduce efficiency and lifespan.


    Anyone got any reason not to use stripped enamel wire, or other wire I have harvested from salvage? I have about 20 CRT yokes and de-gaussing coils in the shed, and a ton of PC power supply looms, as well as lots of other assorted wire.
     
  5. Harald Kapp

    Harald Kapp Moderator Moderator

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    2,651
    Nov 17, 2011
    I totally agree. Connect the tabs from one panel in parallel to increase current output.
     
  6. Harald Kapp

    Harald Kapp Moderator Moderator

    11,517
    2,651
    Nov 17, 2011
    Not exactly. The solar panel is a distributed generator. Electrons are set free across the whole active surface. If the electrons have to travel a long distance from the location they have been set free to the collecting tab, the internal loss of the panel increases.
    This has nothing to do with putting cells in parallel or in series. Ideally you would use series and parallel connections such that under normal operating (load) conditions the complete construction is operated in its optimum operating point, meaning maximum power output.
    Any adjustment you have to make to the output of the tiled panels (be it voltage or current) will decrease the efficiency of the full setup.
     
  7. woodchips

    woodchips

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    0
    Feb 8, 2013
    I think you have misread the panel output ratings, the larger will be 70 milliwatts, the smaller 20 milliwatts, not watts!

    The larger panel is 1/80 m^2, Australia is sunnier than the UK but still only 20-50W m^2 in full sunshine after the panel losses.

    With these outputs the size of wire is pretty irrelevant.

    Bob
     
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