[ZeroGravitas]

There's a concept called "grid parity", where solar PV can deliver energy for the same cost as your utility would charge you for it's provision. This is considered a tipping point, where the economics starts pushing things along harder rather than relying on idealism. It got talked about for years as a goal, but now we've passed it in various parts of the world (starting in those with the combination of lots of sun and high priced utilities).

There's another concept that builds on this called "god parity", which points out that simply distributing energy via a grid has a cost (sometimes more than half of the cost you pay), so if you imagine that you had a tame god that could generate infinite energy for free, but you still had to pay the distribution costs, then if current trends continue, then PV plus batteries would still be cheaper than paying for a grid to deliver "free" energy to your home. It's perhaps not a coincidence that Tesla provides both of the items needed to make this happen, PV and home energy storage.

http://tonyseba.com/how-to-lose-40-trillion/#attachment_1567