Solar panels on a screw down metal roof?

I have a "screw down panel metal roof" where the fasteners are exposed. I've been told that the screws need to be retightened every few years because the screws will come loose over time due to expansion/contraction. I've already found a handful of loose screws (it's about 10 years old).

I'm considering getting solar panels but l'm concerned about losing access to the screws that will be covered by the panels. The company says the only way to get to them would be to remove the panels.

Would it be unwise to get the panels and lose access to the screws? Is there a type of screw that doesn't need retightening? Any suggestions appreciated.