SolarOne recommends system and equipment grounding for your commercial solar lighting. Of course,"Authorities Having Jurisdiction" (AHJs) have the final say. The EGW (embedded ground-wire) is cast into the solar street light's concrete foundation.

Ground Wire EGW

Embedded Ground Wire (EGW): Also known as the concrete-encased electrode, this kit complies with NEC Article 250.52 (A) (3).  This is the grounding method SolarOne recommends most often.