The BIGGEST problem with clean energy

I did a research paper on this exact topic in college. For me the most interesting solution on the large-scale side was CAES/LAES because the facilities to handle this type of storage largely already exist. I would have to dig back through some notes to find sources, but the basic tech needed to store compressed (or liquid) air is already used at the average oil refinery. In addition, many of those refineries have a means of capturing the thermal energy to fully optimize the process. 
And while convincing those companies to convert a refinery into an energy storage plant may be difficult, I know many of the largest oil companies in the world are already looking into how to get more involved in renewables. From everything I found in my research, the potential global impact of converting refineries to storage plants could be both extremely profitable and induce huge growth into the entire energy sector.