Cars will not and can not go back to steam power. Solar cars have been tested and will never replace conventional weight transportation methods. At best they can only transport one person for a very limited amount of miles and that's only if the vehicle is covered in cells. Same thing with air craft. The physics of mass come into play when considering how much energy it requires to move mass over various terrain paths. With a little research one can find charts and stats that will confirm that is it impossible to replace world fossil fuel consumption at the increasing rate of use per year. Here's just one chart that shows how far away anyone is from fossil fuel use replacement. I would dig up more but I realize most are not going to accept the reality of our situation anyway. The train has already left the station and it is not going to stop until it meets the end of the track.