Tracking Sun with Solar Panel - Need Photosensor
If you want to dinamically adapt the position of the panel with the position fo the sun, one good sensor is the panel itself :)

Doing MPPT (Maximum Power Point Tracking), you can also measure the output power and do small movements of the panel to detect the changes in power, and move it accordingly. It will be a bit tricky (and probably not worth) to tilt and rotate it, probably it's more convenient just to rotate.

You may also find this DIY light direction sensor interesting.