You will need to more detail on what "open and close" is in reguards to this panel bracket.
The linear actuator idea is great but if you are fairly crafty you could custom make a linear actuator. I have made one with threaded rod, rod coupler for the moving train, two bearings, and a gear head motor. This doesn't have any position feedback but a rotary encoder could easily be implemented. Do you have a plan on how to orient the panels? I have had good small scale luck with a 30 degree pyramid with 4 photo-resistors in the middle of each face. Biggest downfall to photo-resistors is that they aren't that great for reading direct light levels as they have a logrithmic curve. They have more resolution reading "darkness" than vise versa. This is where the pyramid comes in, it will cast a shadow on one side giving a better difference in values to read with and Arduino.
i bet 20 bucks there is a code already done for this on the internet.
just move it yourself every few weeks.
You could use two servo's that rotate in two different axis: One Up and DownThe other Left to RightThen you could get the voltage readings that the panel gets and adjust it's position in the direction were it gets more power.