The characteristic resistance of a solar cell is the output resistance of the solar cell at its maximum power point. If the resistance of the load is equal to the characteristic resistance of the solar cell, then the maximum power is transferred to the load and the solar cell operates at its maximum power point. It is a useful parameter in solar cell analysis, particularly when examining the impact of parasitic loss mechanisms. The characteristic resistance is shown in the figure below.
The characteristic resistance of a solar cell is the inverse of the slope of the line, shown in the figure above, which, after Green 1, can be given as VMP divided by IMP for most cells it can be approximated by VOC divided by ISC:
Commercial silicon solar cells are typically very high current and low voltage. A 156 mm (6 inch) square solar cell has a current of almost 9 amps and a maximum power point voltage of 0.6 volts giving a characteristic resistance of around 0.067 Ω. As a consequence, connections to a single cell require resistances in the milliohm range.
- 1. , “Accuracy of Analytical Expressions for Solar Cell Fill Factors”, Solar Cells, vol. 7, pp. 337-340, 1982.