Not too long ago I posted a graph by the National Renewable Energy Lab (NREL) that shows all solar efficiency breakthroughs since 1975 on a single chart. I found it fascinating to see just how much progress was being made in all the various types of solar cells (from thin-film to triple-junction...). But what truly matters in the end is how much it costs to produce clean electricity from the sun, and how that compares to the price of dirty sources like coal & gas.
The graph above tells the tale. It only shows progress since 1980, but if the 1970s were included, it would look even more impressive. I was born in the early 1980s, so just in my lifetime, solar went from over $16 per watt (in constant 2012 dollars) to about $1/watt, and like Moore's Law for micro-electronics, there's no indication that the pace is slowing down. In fact, as you can see, it has actually accelerated in recent years (in good part due to massive solar investments in China). We might or might not keep that new rate of progress, but what is certain is that we're headed for parity with fossil fuels (the gray area in the graph), and then solar will beat them.
Both those milestones will be historic for humanity, likely transforming our civilization rather rapidly. I can't wait.
See also: 300,000 mirrors: World's largest thermal solar plant (377MW) under construction in the Mojave
Note: I used the slideshow template so the image was bigger. There's no second slide, so no need to click. We'll soon have the ability to use larger pictures in non-slideshow articles, so we won't have to use this workaround much longer. Sorry about that.