The following schematic is used to measure the solar panel current. The power loss is quite low, only between 0-10A. This schematic can also used as a general purpose DC current meter. The circuit can be used as a positive or negative side of a DC circuit.
The measured current which flows through the 0.01 ohm resistor which causes a small voltage drop across the resistor. To measure this voltage drop, the 100microamp meter is set up series with the 50 ohm and 500 ohm variable resistor in a voltage measurement configuration. The resistor with value 500 ohm is used to adjust the meter’s full scale reading, while the 50 ohm resistor limits the maximum current, protects the meter from passing to much current and burning up.
This circuit needs to be connected in series with a 12V or 24V solar panel array. The meter can go in negative or positive side of the solar panel circuit. The current flowing through the solar panel then the meter will show the load reading.[source : www.solorb.com]