Grounding is the number one thing that electrical inspectors look at to verify that an installation is safe.
The foundation of any good ground system is the actual connection to earth. This has been accomplished and understood in various ways throughout the years but more and more the “concrete encased electrode” is becoming the ground of choice.
Washington state Dept of Labor and Industries is adopting a requirement that ground rods alone will not suffice when grounding a new building or structure. A ground ring or Ufer ground will be required. Here is an excellent article about the Ufer ground. WA L&I is also adding to their Ufer requirements by requiring that either the rebar system is inspected before the concrete pour OR having a 2nd rebar stub-up from the rebar system at least 20′ away from the Ufer ground attachment point. That way an inspector can verify continuity between the 2 stubs and confirm that the rebar isn’t just poked into the concrete after the fact. Unfortunately the electricians often arrive at the site long after the concrete has been poured so it will be the builders job to make sure this Ufer ground system is installed properly. If the builder fails to install a Ufer ground then a coper wire will need to be buried all the way around the building (ground ring) at considerable expense.
Tying the ground from the solar array into the wire coming from the Ufer ground point (grounding electrode conductor) is the best way to assure that the solar array and associated equipment is also grounded.