Hyundai tried it on a production Hybrid car

https://www.hyundaimotorgroup.com/en/story/CONT0000000000091...

Their PR math uses a 22.8% efficiency rate at 0 degrees tilt with a total of 204W production, 5.8 hours per day = ~1,300 km per year = ~2.5 miles/day. Testing was conducted in Korea.

The real world results were negligible.