Those ACS712's are not looking right, current measurements are generally done in series on one leg of the supply wiring, not in parallel as your diagram would indicate.
Connect your solar system together and place a wire from ground of the Arduino to the battery negative lead and connect all of your measurement return leads to that point. Insert the current sensors in the positive leads of the power supplies (Battery and solar panel) connect the sensor output common leads separately to the SAME point on the Arduino. This forces a star topology that prevents ground potential differences caused by load and charge currents from affecting the measurements as a whole.
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