Renewables are great, but I'm not sure they would be able to support an entire economy. One of the few great things about fossil fuels and specifically oil is that it is a power source that can be stored in a dense and stable form. Renewables can't really be stored in this manner and therefore can't easily be exported beyond reasonably short distances. Saudi Arabia therefore can't rely on selling renewable energy to the USA, China, and the EU to support their economy like they do with oil.