Solar panels on cars make more sense than a decade ago
Things got better in 2017, when Toyota started offering the Prius PHV with an optional solar roof in Japan. That solar system charges the main battery only when the car is parked, and can add, on average, 1.8 miles to the car’s driving distance each day, with a max of around 3.8 miles. Solar power can’t charge that main battery—called the traction battery—while the car is being driven, however. During that time, the power goes into the 12-volt auxiliary battery, which gives juice to car systems like the radio.