Monday, May 16, 2011

Urban Solar - Take 1 Post 2


Went to an event at the New School in NYC today about Hydraulic Fracking and its potential effect on NYC water. More on that later. (Hint: It's freaking catastrophic!)

So where were we in our little solar adventure? Ah  yes. Broken dreams.

As you probably know, solar cells, like the 6" x 6" monocrystalline cells I purchased are REALLY fragile. To put it in perspective, imagine a thin sheet of glass- maybe the thickness of 2-3 sheets of paper. The sad part is that I knew this going in and still managed to break the first one. Here's how:

I watched several videos on how to tab solar cells. Tabbing is what you call soldering the tabbing wire to the cells. This tabbing wire ensures that the current along the negative side (front) of the solar panel travels along the entire cell and can be linked to the next solar cell. Monocrystalline cells like mine tend to have 3 bus bars going down the front.  Polycrystalline cells have 2 bus bars, and amorphous cells have no bus bars. The tabbing wire is slightly wider than the bus bar and has solder built in, right on the tabbing wire itself. Each strand of tabbing wire should be cut to about 2x the length of the cell so that it can be run down the length of the front of one cell, then down the length of the BACK of the next cell.

Before you can attach the tabbing wire though, you need to use flux. The flux pen should be run down each of the bus bars in turn. It cleans oils and oxides off of the bars and ensures a better solder.
I took the flex pen and "wet" it by pressing it onto a small piece of aluminum foil. Nothing special about the foil, it's just what I had nearby. The liquid in the pen came gushing out. Ok, not like Old Faithful or anything, just A LOT faster than I expected. I was able to rewet by dipping in the pool of smelly brown/yellow liquid in my aluminum foil.

Now, super eager to get to the business of actually DOING something, I placed the solar cell on top of a piece of cardboard, to protect the table from the heat of the solder.


Withing a few seconds, the uneven distribution of pressure (aka ME) on the cell caused it to crack. This leads me to my first gotcha of the process:

  • The surface behind the solar cell should be hard, sturdy and absolutely flat. I've heard good things about using a clean piece of sturdy glass that has been laid on a hard surface (table, work bench, etc). The reason for the glass is that it helps dissipate the heat from the soldering iron and prevent damage to the cell. 
And why did I need so much pressure to solder the cell? The second gotcha is:
  • Get a (wo)man's soldering iron. This cutesy little 23 watt p.o.s. did absolutely nothing. It was unable to melt the solder on the tabbing wire. With a good soldering iron, you should be able to run the iron down the length of the cell in about 1-2 seconds and have a good solder. The wattage doesn't indicate temperature, it's a measure of the "reserve" heat. When you touch the tip to the cell, heat transfers to the tabbing wire, the bus bar, and the whole cell. At 23 watts, the soldering iron couldn't make enough replacement heat to get the tab solder up to the melting point. Sadness.

    So yeah, no crappy soldering irons. I'm getting a 40 watt tomorrow. I'll try with that and see where it takes me.So far, I have a pool of smelling yellow corrosive stuff, a cracked cell, and zero tabbing.

    Maybe I should have tried melting concrete instead. Looks easier.

    Melting Concrete with the Sun

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