It's a process that is absolutely underway and making great progress, even the USA now generatea more from solar than from coal, many countries like Scotland are already producing over 90% of their electrical use from renewables with only 2% from fossil fuels.

It's worth noting too that these numbers are only grid based usage and a lot of solar is direct use, often being stored in an electric car rather than sold to the grid - with rooftop solar at home and at work it would be possible to use a car without requiring any of the oil extraction, transport and refining faculties. I don't know how many people it would take using solar cars before a single oil well goes untapped but I do know if we get to a point where no one is using gas stations then that'll be an awfull lot of horrible polluting infrastructure we don't need, just carrying the fuel through wires instead of in tanker lorries is a huge saving alone.