It's far enough along that Germany is replacing all of it's nuclear power plants with solar power plants. Is it perfect now? No, but there have been some pretty decent breakthroughs in recent times that, in the next 20 years, solar will be one of the dominant and cheapest energy sources on the planet, replacing much of the coal and nuclear facilities. I'm not some starry eyed dreamer either. I'm very critical of technologies that don't work, and in the past, solar was not to the point of becoming a major power source, but now we're getting there.