What is the Packing Density of the solar module?

The formula

​The solar module is made up of a number of solar cells connected and packed to each other in a certain pattern. The extent of the closeness of the solar cells in the module is defined by the term Packing density. 

​In other words, it tells how closely the solar cells are packed to each other. The higher value of the packing density means that there is less empty space between the solar cells while a lower value of the packing density 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.

• Packing density = Actual area occupied by the solar cells/Total area of the solar panel

It is clear from the above formula that the value of the Packing density 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 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.

Different types of Packing Densities

​The packing density 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 the packing density and the efficiency of the module. This process increases the packing density to 80%.

(*We cannot cut the wafers to make is exact square as will lead to loss of material and is not economical)

• 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%.

Packing Density trend

Conclusion

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.