The research in petroleum and nuclear energy is many times greater than that for renewable energy sources. However, the fact that the USA government is doing very little shouldn't be a cause of too much concern. The USA is now competing in a global marketplace. Australia, Japan, Indonesia, India, China, and many other countries are making substantial progress in PV and other renewable energy developments. Plenty of global citizens will have resolved their own energy problems when Americans really begin to suffer.
Solar cells are already efficient enough.
These interests need to see a profit from renewable investments before they will change. There is not enough solar energy falling on the surface of a car to give the performance we have all come to expect. All-solar cars which run with energy from collectors on the car itself are unwieldy. Solar race cars have a weird shape, and this shape is due to the diffuse nature of solar energy. Just the same, solar powered cars are quite useful to industry.