Early reports of roof leaks were probably associated with improvised mounting methods or just plane old sloppy work. The roof leak problems have essentially been resolved, given a good installer who does the work. However, any roof penetration can be the source of a leak, its possible.
I have to admit that any opening in a roof gets me concerned. I have one roof mounted solar array, and a ground mounted array, so far no roof leaks in about 10 years, so far, so good. My arrays are fixed, no adjustments are made to seasonally tweak the power output. The ground array has the advantage of easy access, the roof array is on a steep pitch roof, not something I want to have to go fiddle with.
Having a mounting system that has an air space between the back of the panels and the roofs surface for air circulation is essential to keep the panels cooler, but that has more to do with improving the efficiency of the panel, the hotter the panel the lower the output power.
I am not aware of any thermal expansion problems related to modern solar panels construction. Having said that I always run a tiny bead of good silicone caulk around the panels aluminum frame to add my own barrier to moisture, call me cautious, ha. Thin film panels seem to be particularly sensitive to any moisture intrusion, so buying a well designed panel is a good thing for long life.
Most solar panels come with a warranty these days, a guarantee that the panels power output will exceed 80 percent of its original rated power output power after 20-25 years, depending on the manufacture. As far as I know the manufactures are honoring the guarantees, your experience may be different, depends on the company.
