To provide higher conductivity the top of a cell has a series of regularly spaced finger. While tapered fingers theoretically provide lower losses technology limitations mean that fingers are usually uniform in width. The resistive loss in a finger is calculated as below. At the end of this page there is a graph showing how the parameters affect power loss in the cell.
Calculation of Power Loss in the Fingers
Consider an element dx at a distance x from the end of the finger.
The current through the element dx is: ,
where Jmp is the current at maximum power point and Sf is the finger spacing.
The resistance of the element dx is: ,
where wf is the finger width, df is the finger depth (or height) and ρf is the effective resistivity of the metal.
The power loss in the element dx is:
Integrating x from 0 to L gives the power loss in the finger: