How has big oil kept them down all these years?
For the most part they haven’t played a part.
Being a manufacturer for major components in each of these systems, there have been significant challenges to make equipment efficient enough and high enough ROI to make them viable. The challenges are pretty significant but the progress has been pretty amazing in the past 10 years.
Places in Arizona for example produce far more solar energy than they can use so they PAY to have it exported to other states.