All you typically need is a very small resistor and a high gain amplifier...
How high is the gain is depended on your current demands and the value of the resistor,
The gain is easily adjustable so it's recommended over the resistor change.
You SHOULD by the way calculate the wattage of the resistor, which is the current that goes through multiplied by the voltage drop on the resistor.
By judging using as a power supply the solar panels, you shouldn't need "big" resistors (wattage)...
Some AVRs have a 100x gain on some ADC channels (see the datasheet)
You may be able to get away with it, if the current demands aren't great ;-)
I am using a PIC micro controller, to be specific the PIC16F1827. I don't quite understand how a resistor and high gain amplifier could be used to measure current though. Could you explain?
Here are the specs for the panels:
Peak Power (Pmax,W): 270 W
Power Tolerance (%): ±3%
Max Power Voltage (Vmp): 35.5 V
Max Power Current (Imp): 7.61 A
Open Circuit Voltage (Voc): 44.5 V
Short Circuit Current (Isc): 8.30 A