I've only read the free portion of this post, but even that is a worthwhile discussion of how solar costs are plummeting much more than many people realize and where the margins of greater efficiency can be wrong out even further.

Can Solar Costs Keep Shrinking?
The costs of some parts of solar farms will drop to near zero. But some obstacles remain to make this energy cheaply available everywhere. As a result, the entire energy industry will change. What are those obstacles? How will the industry change?
unchartedterritories.tomaspueyo.com