Monocrystalline modules are the most efficient PV technology commercially available, and can convert sunlight to electricity at an efficiency of up to about 20%. Highly purified silicon and large amounts of heat are used to make a cylindrical ingot, from which cells are sliced. This cutting results in significant kerf waste, as some of the crystal is turned into dust. Additional cutting occurs when square cells are hewn from the middle of what is originally a round ingot. Diamond-like spaces between the corners of cells are typical of monocrystalline modules. But any blank space on the module’s surface lowers its overall efficiency (W per ft.2), regardless of how efficient the PV cell technology is.
Polycrystalline modules have cells that are also cut, but from a large cast ingot that requires less energy to manufacture. However, cells produced this way are about 4% less efficient than monocrystalline. Often, the polycrystalline structure is evident in appearance, with cells having a much more heterogeneous pattern. Because the cells can be cut into squares, there is much less blank space between the cells, which can narrow the efficiency gap between mono- and polycrystalline modules. In some cases, it can be difficult to distinguish between the spacing between cells and the conductors that run up and down the cells, connecting them together.
Other Available Cell Technologies
Mono a-Si (hybrid monocrystalline amorphous silicon) modules by Sanyo
UMG (upgraded metallurgical-grade silicon) made by Canadian Solar, which now offers a 25-year linear performance warranty (see below)
Thin-film silicon modules are not listed, as they are primarily used in utility-scale installations. They usually cost less per watt, but are much less efficient, and thus require more space and mounting structure to install an array of the same rated power.