In last few years solar technologies are developed with the exponential rate, whether it is solar storage, Net metering, Remote monitoring or any other segment, but the prime focus of technology is, How to increase the efficiency of the solar panel.
Solar panels are not only the most important and expensive component in a solar plant but also consumes major space in any solar plant. Thus increasing solar panel efficiency means generating more power within the reduced area, which in turn reduces the cost of land or Roof required for a particular capacity of the solar plant. Therefore since few years, a lot of experiments are going on to increase the efficiency of solar panels.
Nowadays most of the solar panel manufacturers are promoting their module based on the number of Bus-Bars available in their module, they claim higher the number of bus bars, higher the efficiency of the panels.
So let’s understand technically how the number of Bus-Bars is affecting the efficiency of panels?
If we observe above solar panel closely, there are 3 Parts covering its top surface:
1) Gap: While assembling solar panel there is always some distance maintained between the fabrication of two cells, to accommodate any kind of expansion when it is exposed to high temperature.
2) Fingers: Fingers are the horizontal thin lines within solar cells, these are the metallic wires, which collects current and delivers to connected Bus-Bars.
3) Bus-Bars: Bus-Bars are the vertical lines, made of silver paste or high conductivity wires, which carry the cumulative current of fingers & are used to interconnect other cells, to develop the module.
So in a solar panel , multiple cells are connected in the series to generate the required voltage level, like if a single cell is of 0.5 Volt, we need to assemble 60 such cells in the series to generate 30 V solar panel Voltage and 72 such cells in the series to generate 36 V cumulative solar panel voltage.
When the solar panel exposes to the sunlight, cells start generating current. This current flows through fingers to Bus-Bars and Bus-Bars of each cell are connected to neighboring cells Bus-Bars and they form a complete circuit. This Bus Bar circuit carries the cumulative current of the module to output terminals.
Now in overall process current flows through fingers and Bus-Bars to reach the output terminals, Thus the factors affecting the efficiency are
1) Fingers Resistance
2) Bus-bar Resistance
3) Bus- Bar & finger wire metal quality
So the efficiency of modules can be increased by reducing Finger resistance & Bus-Bar resistance & by increasing the quality of the metal wire.
Now let us understand, how increasing the number of Bus-Bars affects the efficiency of the module. If we increase the number of Bus-Bars in a solar cell, length of finger wires may reduce, which will reduce the finger resistance, similarly by increasing no. of Bus-Bars, cumulative width of Bus-Bars will also increase which causes the reduction of Bus-Bar Resistance too.
Now if Bus-Bars & Fingers are having low electrical resistance, the loss of current during the path will be less, which will allow flowing more current through the path. Let us understand this with a simple example of a car moving from internal road to highway till its destination, where let us consider Bus-Bars as highways, fingers as internal roads connecting to highway & current as the number of vehicles.
Case 1: When highways are less, long connecting roads are required to connect these highways. In such case, as connecting roads are narrow and long, in peak time car will experience more traffic to reach to the highway & once it reaches the highway, it will experience more traffic in highways also, as the number of highways is less. In this way, the car will take more time to reach the destination so, within the given time, less number of cars can travel along the highway.
Case 2: Now if we increase the number of highways, connecting roads will become shorter. In such case, as narrow roads are reduced, the car will reach to the highway with less traffic & further traffic on the highway will also get distributed to additional highways. So in this case car will take lesser time to reach the destination & in a given time period more cars can travel to the highway.
Thus we can say that by increasing number of highways, more traffic can travel in a given time. In the same way, after increasing Bus-Bars in solar modules, current needs to travel less distance in fingers which are thin wires & at the same time cumulative space in Bus-Bars is also increased, which offers low resistance path to current, thus current carrying capacity of the module will increase. This means for the same module, if we increase no. of Bus-Bars, its current generating capacity will increase in the same solar radiation. Thus higher Bus-Bar Panels gives more generation compare to lesser Bus-Bar Panels.