Cars and vans use 16.5 billion litres of diesel and 15.5 billion litres of petrol

HGVs and busses use 8 billion litres of diesel, about 20% of the total of cars and vans. Agriculture adds another 1.5b and trains half a billion, so call it 10 billion litres, 30% of total fuel use by cars and vans. Push it 50% up from 80TWh to 120TWh if you want and require 15 million roofs

Of course the most economic way to deliver solar isn't by putting it on the roof