The packing density of solar cells in a PV module refers to the area of the module that is covered with solar cells compared to that which is blank. The packing density affects the output power of the module as well as its operating temperature. The packing density depends on the shape of the solar cells used. For example, single crystalline solar cells are round or semi-square, while multicrystalline silicon wafers are usually square. Therefore, if single-crystalline solar cells are not cut squarely, the packing density of a single crystalline module will be lower than that of a multicrystalline module. The relative packing density possible with round verses square cells is illustrated below.
Sparsely packed cells in a module with a white rear surface can also provide marginal increases in output via the "zero depth concentrator" effect (SERI), illustrated below. Some of the light striking regions of the module between cells and cell contacts is scattered and channelled to active regions of the module.