For a single solar cell (6 inch) it produces current of about 10 A, Is there an equation or method to calculate the current passing through each finger? How do the fingers extract the current from the cell surface?
Silicon solar cells are metallized with thin strips that are printed on the front and rear surface of a solar cell. These front and rear contact strips are the busbars which conduct the electric DC power generated by the cell.
Silicon solar cells are metallized with thin strips that are printed on the front and rear surface of a solar cell. These front and rear contact strips are the busbars which conduct the electric DC power generated by the cell. Perpendicular to the busbars are the super-thin and metallic grid fingers , which are connected by the busbar. These fingers collect the generated DC current and deliver them to the busbars.
In solar cell design, the balance between finger resistance losses, shading and reflection losses is optimized.
For calculation of the power loss in a single finger, several assumptions are made. A constant width is assumed and a uniform generated current is also assumed, and also that the current flows perpendicular to the finger (no current flows into the busbar directly.) Consider an element dx which is at a distance x from the end of the finger. The current flowing through the element dx is: x JMP Sf where Jmp: the current at maximum power point Sf: the finger spacing. Then the resistance of the element dx can be calculated as: dx ρf / wf df where wf: the finger width, df: the finger depth (or height) ρf: the effective resistivity of the metal. The power loss in the element dx can be caclculated using I2R as below: I2R= dx ρf / wf df * (x JMP Sf)2 By Integrating x from 0 to L we can calculate the finger power loss as per the equation below:📷Thus by minimizing finger resistance losses we can ensure we have an efficient design for our solar cell.
Dear Abdulwahab Hasan ,
Adding to Hadi Jabbar Alagealy the photocurrent is distributed homogenously throughout the junction of the solar cell assuming it is homogeneously illuminated by the solar radiation. So, the photocurrent crosses the junction vertically and then bend laterally to the left finger and and to the right left finger where the lateral currents will be collected by the two fingers bounding them. Half the the photocurrent will be collected by each bounding finger.
So, assuming the the area between the two fingers is Aff and photocurrent density is Jph then the current that will be collected by either bounding fingers= Jph. Aff/2. If the finger collects from the both side and the structure is geometrically symmetrical then If = total current in the figure collecting form both sides= Jph. Aff. Aff is the collection area by one finger.
If the total current is Iph and the area of the cell is Acell, then
Jph= Iph/ Acell.
Fo the distributed solar cell model please see the paper:Article A distributed SPICE-model of a solar cell
Best wishes
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