I just saw the Prius added solar panels too. It makes sense for a car that's parked a lot.
>>600W
Let's see, we get on the best days about 12kwh out of 300w array. So roughly 2kwh out of the panels. Let's say 4 since we have some shade trees. That's 5% of the total, which gives you maybe 20 miles * 14 miles* on a long summer day, or more to the point, lets you camp indefinitely without running down your battery. The latter point is something I was thinking about with EVs.
*update: Bad math. Range is 280 miles. 5% best case.