I like your project. I wrote a "Solar" program in BASIC about 30 years ago. There is a lot of considerations as you work through this problem. Longitude and latitude of the solar site, the solar day of the year. Azimuth, and position of the sun, etc., etc. 30 years ago, it was positioning panels built of old automobile radiators to supply heat. With the availabilty of small microprocessors like the Arduino, much of the celestial math can be eliminated, and just differentiate between multiple light sensors, and logically move to the brightest as your target. Keep up the good thought process, us old guys are counting on you!