The mass deployment of solar energy will be largely dependent on how cheaply it can be stored (this is why fossil fuels are hard to transition away from; they represent highly concentrated sources of stored solar energy in chemical form).
Electricity is expensive to store, but I hear that solar thermochemical fuels can also be manufactured, thereby created a liquid fuel source...
To add on to this, Stanford did do a study on sodium based batteries, which can be manufactured much more cheaply than Li-Ion batteries.