Here's the alternative that I used. I had Solar Guys install an electric (not solar) garage fan at a cost (10 years ago) of approximately $100. It is installed to pull air through garage door vents, into the garage, and out through the fan pulling the air into the attic.
It keeps the garage quite cooler, shaded air temperature, which is fine for us.
I'd say it also keeps my whole house cooler since the attic gets ventilated too.
Electrical cost is negligible and I think I save on A/C costs since my utility bills seems pretty reasonable.
Energy-Saving Solar Garage Fan Install | The Villages & Central FL