The cost of silicon solar panels has been falling precipitously, with no end in sight.
Naturally, falling costs mean solar installation has been exploding worldwide.
By the time new coal-fired power plants come on-line in the U.S., solar will already be cheaper.
If you want to understand what kind of revolution this will bring about in power production, check out this analysis from Jonathan Koomey of Stanford University:
Here's an interesting thing for people to contemplate: As solar reaches grid parity based on retail prices we'll start to see big changes in what is now called the peak demand period in most regions (summer afternoons, when air conditioners run full blast). The system is now set up to meet that peak demand with lots of inefficient gas combustion turbines that we can either retire or repurpose once [solar photovoltaic] comes in full force. And when you combine that development (which is coming over the next 5-10 years) with the advent of price responsive demand you'll see big changes in how the utility system operates.