The method I have used in the past is to add a resistor in the ground side of the PV panel and measure the voltage across it with one analog input, then using a potential divider, drop the voltage at the 'top' end of the panel so it is within a safe range for the PIC and measure it on another analog input. You should protect the PIC from over voltage just in case a fault occurs. You can then calculate the current by measuring the voltage drop across the ground side resistor, measure the voltage by subtracting the bottom from the top and also calculate the power being drawn from the panel by multiplying the two together.
Brian.