I have a small multi-junction solar cell that I will be taking measurements of short-circuit current and open-circuit voltage periodically in order to approximate an IV curve for the cell.
I have decided that the best method to measure the current is a shunt with an op-amp providing amplification to a microprocessor. I have previously used a hall effect current sensor, but interference from a nearby source of magnetic fields contaminated my readings. A shunt is more tolerant to this sort of issue.
The solar cell will be providing a voltage of between 1v and 2.5v, and a current of 5~20mA. What resistance should I use for the shunt resistor, and how should I consider a resistor for this application?