a thought on the sensors. what it seems you really want to do is to balance the left and right to be equal.
all the center does is to verify that the light is between the outboard sensors.
since there is no way to tell the center if it is on the brightest light without it sweeping back and forth, stability comes from the outboard sensors being equal.
this is the heart of solar panel tracking.
difference = up - down
if( difference <= 10)
if ( difference >= -10)
do nothing as you are close
if (difference > 10)
move up
if ( difference < -10 )
move down
blink without delay - check every 10 seconds.