How strong of a STEPPER MOTOR do I need ?

I am working on a solar tracking device project. I am using a stepper motor to move the solar panel in the direction of the SUN. My panel is going to be around 3-4 kg. Now, I was wondering how strong of a stepper motor do we need. We will be connecting the stepper motor shaft to a rod using a coupling n the rod will have the panel placed on it. We have a stepper motor and the specs are:
• Soyo SY57ST76-0686A Unipolar Stepper Motor
• Voltage: 12vdc
• Resolution of 1.8 degrees/step
• Torque of 125 oz/inch
• Precision of ±5%
• Single shaft

Is the torque enough to move and hold the panel ? or we need to buy a stronger motor ?

Your motor should do it. But you could always use a lever system or use multiple gears to lower the ratio.

You may want to look at a linear actuator device attached to your motor.