The year the system was installed will affect what warranty’s may still be in place. Often the installer’s workmanship warranty may have expired, or the installing company may no longer be in business, but the manufacturer’s warranty for the PV panels and inverters may still be in place.
Ask the current homeowner for any documentation received from the original installer, ideally they should have a homeowner’s manual which provides information including the system design drawings, product information including serial numbers (needed for future warranty claims), and most importantly login credentials for the online monitoring platform which allows you to track the performance of the system.