Not use current limiting resistor for switching device on off using TIP122 possible?
You do not need a series resistor. Think of the transistor as a switch.

You do need a base drive resistor from the PIC.

BUT use a MOSFET - it will do a better job than the TIP122 and will cost no more.

Rushing out. Look at www.digikey.com. Search for MOSFET N Channel, set filtersto 100V min and say 10A and search based on lowest price in stock in 1's.

More later maybe ...