The Birth of a Solar Cell

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The module assembly process begins with the cells' being tested and grouped according to output current. Then units of similar capacity are electrically connected with ribbon wire, by soldering the front contact of one cell to the back of the next. This series wiring allows each cell to contribute about 1/2 volt to a panel's total output.

The array is then set face down on a piece of tempered low-sodium (for maximum solar transmittance) glass, over which has been stretched a thin sheet of polyvinyl butyl (PVB) plastic. When another sheet of PVB is placed on top of the assembly, the cells become sandwiched between two waterproof layers.

Once the power leads have been routed through two small slits in the plastic backing, a heavy sheet of white Du Pont Tedlar plastic (which is impervious to moisture) is laid over the back of the array as further insurance against water penetration. The final layer is a sheet of metal (such as steel or aluminum) fitted over the back to protect the panel from damaging blows.

To remove any moisture, the module is set into a laminating press, and trapped air is pumped from between the layers. Pressure is then applied to compress the assembly, and the temperature is raised to a point at which the PVB becomes slightly viscous . . . allowing it to flow into and fill the void between the cells.

After the module has cooled, a bead of silicone sealant is run along the edges of the thin panel, and a sturdy metal frame is wrapped around the 3/8"-thick assembly. The housing will not only protect the module, but also carry heat away from it when the unit is finally placed under the intense rays of the sun. The finished panel is tested once more for output and is then ready for shipping.

As you can see, the manufacture of photovoltaic panels isn't a backyard technology that's being exploited by big business. In stead, it's a fitting task for big industry . . and delivers a product that may soon be found in many of our back yards.

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