Solar-Electric Panel Technologies

Multi-Crystal Silicon

Multi-crystalline (also called polycrystalline) silicon modules are slightly less efficient (12-15%), but are less expensive to produce. The manufacturing process for polycrystalline cells involves casting of molten silicon into molds where the material hardens into “ingots”. The resulting solid mass includes multiple intersecting crystal lattices and gives these cells their characteristic “jack frost” appearance.

Polycrystalline modules have varying grades based on the size of the crystals and the number of impurities, both of which are largely determined by the cooling rate of the material. Larger crystalline wafers are more expensive to produce, but are more efficient because of their tighter molecular structure.

String Ribbon

Physically and electrically similar to polycrystalline is the “string ribbon” technology, currently used exclusively in the production of modules from Evergreen Solar. In this process, the melted silicon is formed into thin sheets by drawing it up from a vat of molten silicon in a ribbon-like film suspended between two wires or strings—think of a child's bubble-blowing wand or ring and you won't be far from the mark. The key advantages to this process are that the resulting cells need not be sliced from a solid mass—they are simply laser-cut from the continuous ribbon—like using a scissors—so there’s less waste; and the cells are thinner, therefore less silicon is used. String ribbon-based modules are slightly less efficient (10-14%) but cost less to manufacture than traditional crystalline types.