Solar-Electric Panel Technologies

Most solar-electric panels commercially available today are made from silicon and can be divided into three main categories, based on how they are manufactured:

• Single-crystal silicon
• Multi-crystal silicon
• Amorphous silicon

The technologies used to manufacture solar-electric (PV) cells (the building blocks of solar panels or modules) and the differences among the final products are described below.

Crystalline Silicon

Modules made from both mono- and poly-crystalline silicon cells are the most expensive to produce since very pure silicon is required— in fact, the same material is used in the manufacture of computer processor chips. The purification and crystal-growing processes are very energy- and time-intensive and, until recently, there have been few manufacturers producing this feedstock material. (There are more players in this market now, but module prices remain high in the U.S. as the European market absorbs most of the production stream.)

Single-Crystal Silicon

To manufacture single-crystal (also called monocrystalline) cells, the purified silicon is first melted, then a crystal is grown by placing a “seed” crystal into the molten material and drawing it slowly up from the heated crucible. The seed sets the pattern for the growing crystal, resulting in a large, cylindrical crystal called a boule. The boule must be sawn into very thin wafers which are the basis of PV cells.

Monocrystalline silicon is the most efficient at converting solar energy to electricity because the cells’ molecular structure is arranged very uniformly, allowing for the most ideal transfer of electrons through the material with the fewest interruptions. Cell efficiencies for commercially available monocrystalline PV modules currently reach about 17%, with module efficiencies generally being a bit lower.