As a solar installer you may have come across 4BB/ 3BB/ 2BB on solar panel data sheets. 4BB implies it is a module with 4 Bus Bars. 4 bus bar cells are the latest technology in the market and they have several benefits over 3 bus bar or 2 bus bar modules. So what does this exactly mean for the generation of your solar plant?
1. Higher Output per cell = Higher Efficiency
As the distance between adjacent bus bars is shorter in 4BB modules, the current path is shorter leading to higher output. Price wise this may not make a difference as solar panels are sold in the market on a Wp label at a Rs/ Wp price. i.e. you may have 3BB or 4BB modules with an identical power rating of let’s say 310 Wp. For very large solar plants where area covered is important, even small gains in module efficiency make a difference as 4BB modules are able to pack a higher Wp in the same area.
2. Lower Residual Stress in 4 bus bar cells= Lower Degredation
When conductors are soldered onto solar cells to assemble them into solar modules, the soldering activity leaves behind residual stress in the cells. Over time the residual stress converts into micro-cracks which ultimately reduces the generation.
Due to shorter distance between the bus bars in 4BB cells, the residual stresses are lower in 4BB modules by up to 10%. Hence long term generation of 4BB modules is expected to be superior as degradation is lower.
3. Manufacturers- Upside and Downside
The automatic soldering machines used to assemble 4BB modules are different, hence it requires intensive capital investment by the module manufacturer to upgrade their equipment.
On the upside, assembled 4BB module when compared with industrial type 3BB solar cells and modules, demonstrate average fill factor gains of 0.6% on the module level- which means higher module efficiency. A reduction in silver paste consumption of about 50% is also observed, resulting in lower material cost. Another benefit for the solar module manufacturer is that with the same number of cells they can manufacture modules with higher wattages and sell them at a higher net price per module after sorting.
So overall, we find, that 4 Bar Bar modules are an upgrade in technology. Having higher efficiency and generation over life they will result in higher generation over life of your solar plant.
In case you are looking for more a more technical deep dive, the below slides by Jinko Solar give a good overview on the difference between 3BB and 4BB cells.