The solar cell’s packing density refers to the area of the module that is covered with solar cells compared to the other module area which is blank. The packing density of the solar module affects the output power of the module and the module’s operating temperature as well. It is dependent on the shape of the solar cells used. As an example, single crystalline solar cells are always round or semi-square, while the multicrystalline silicon wafers are normally square. Thus, if the single crystalline solar cells are not cut as a square, the packing density of the single crystalline module will be lower than that of a multicrystalline module.
For the packing density of round and square cells, the round ingots of Cz material cause a low packing density so the edges of the cells are cut off to produce semi square cells and a higher packing density. For multicrystalline material, it is cast in square blocks so as to give a high packing density.
Sparsely packed cells in a module which has a white rear surface can provide marginal increases in output as well by the effect of the zero depth concentrator , where some of the incident light striking areas of the module between cells and cell contacts is scattered and channeled to active regions of the module.
The solar module is composed of a number of solar cells connected in a specific pattern. So, it defines how closely packed the solar cells are to each other. The higher value of it means that there is less empty space between the solar cells while a lower value signifies more empty space between the solar cells or the solar cells are loosely packed. It affects the output power and the operating temperature of the module.
Actual area occupied by the solar cells/Total area of the solar panel
It is clear from the above formula that its value is area related, more occupied area and less empty space (generally referred as the white area) means more Packing density and hence more efficiency.
The rear sheet on which the solar cells are embedded and is white in color and when the light falls on the white surface, it is reflected and marginally improves the efficiency of the solar cells.
The different types
It depends on the shape of the solar cells whether it is round, pseudo-square (semi-square) or square.
Round solar cells: The solar module made up of round solar cells generally has low packing density (70% packing density) because when these round solar cells are connected, they leave a good amount of the empty space between them. The monocrystalline silicon cells are circular in shape.
Semi-square or Pseudo-square: In order to increase the efficiency, the circular solar cells are cut to get the semi-square shaped which in turn increases it and the efficiency of the module. This process increases it to 80%.
Square cells:The wafers of the multi-crystalline are of square shape and these are also cut in the same shape hence have the highest packing density of 90%.
The packing density in this context particularly talks about the wafers-based module but not the thin film modules. As of today, the wafers-based technology supports the 90% of the modules.
Although, the efficiency of both the mono-crystalline modules and the poly-crystalline modules are nearly the same, the multi-crystalline solar panels are preferred over them and are widely in use because of their higher cost and the lower packing densities of the mono-crystalline modules.