Although a Pi is somewhat overkill, having the underlying Linux O/S provides so many advantages (remote access, remote code maintenance, logging, watch dog applications,)
If this is a remote application, or highly experimental, consider an RPI.
Otherwise Arduino's will easily manage the task, and generally will provide far better power consumption (may or may not be an issue).
Personally being a Grad project I would use a Pi, and log the crap out of the rig, sense and record everything (position, times, solar levels, power/voltage/current levels, battery state, enviro, rig, system temperatures, night time events). Important to any Engineering (academic) project is not just if it works, but also the data you collected so you can plan how you will make system improvements etc. I worked as Eng Lecturer for some years and I always reinforced that with any project or experiment, expect it to fail, but plan how you will still show success with the data you collected, lessons you learnt. Engineers are paid to solve problems, not assemble kits. I have often granted top marks to failed projects due to their recovery plan and the lessons learnt, over projects that just switch on and work with no issues.
If your running long term logging, consider a USB stick for backup of the log data, in case of SD failure. Just a CRON job daily to copy all the log files onto the USB stick. Cant do that (easily) with an Arduino. Also consider an independant power source (own battery/UPS hat) for the RPI so it can keep logging during system wide failures, and manage its own clean shutdowns. This is a must with all solar powered projects. You want to know why it went down, not just that it did go down.
..the only thing worse than a stupid question is a question not asked.