>>They won't save oil.
But they save *energy* which can be used in any way, including the saving of oil. For instance, cracking water into hydrogen and oxygen. PV isn't an energy storage medium like hydrogen. It's an energy source, and can be used in as many applications as we use electricity today, and others yet to be developed. It won't *create* oil, but it can supplant its use in many ways.
The problem with replacing oil for its most important use isn't in the cracking but in the energy density and ease of handling as a vehicle fuel.
If it were just a matter of substituting energy sources you would have seen plenty more of it by now.
Petroleum products are just incredibly convenient.