Wrapping and connection of cells.
The front grid of the cells, on the one hand, consists of the “fingers”, which is the grid of conductors that collect the current generated in the cell, on the other hand, of the “bus bars” which are the current collectors where all the fingers are connected and which carries the current to the outside.
The wrapping of the cells consists of soldering the tinned copper strips (busbar) on the fingers. In the current market the tendency is to use panels with 5 Bus Bars, that suppose improvements in the yield of the solar panels that incorporate it.
The busbar of the solar cells are made of copper, covered with silver. The silver coating is necessary to improve the conductivity of the current and reduce oxidation.
In order to find the optimum design for the busbar number, the losses due to the electrical resistance of the material and the surface they occupy inside the cell must be taken into account. As an optimization, round conductors can be designed which, compared to rectangular wires, guarantee less shading due to their reduced space.
For a smaller number of Busbar, the thickness of these must increase to withstand the current flowing through them. This leads to a greater heating of the cells due to the Joule effect.This higher number of busbars reduces the distance between the busbars, which decreases the internal resistance losses.
The greater number reduces the effective length of the fingers between the busbars, which decreases finger resistance losses as well as microcrack impacts.
In any case, the interconnection process is always the same, that is, the Bus Bars that are on the front face are soldered to the back face of the next cell and so on.