Generally, LDR's don't work particularly well in this application.
Also, you really need a timing circuit, so it only wakes up & seeks briefly every 10 - 15 minutes.
You can also pwm the motor signal to limit the speed.
RedRok did one like this, but it used an exotic (unobtainium) controller chip.
I did one, using generic components. In user diaries a few years back.
Still haven't built the mechanical mount for the panels.
Amanda