From Bloomberg: It has never made less sense to build fossil fuel power plants.
According to this article, the cost of solar power is now below that of coal and gas in at least nine US states, including Arizona, Texas, New Mexico, Nevada, California, Louisiana, Mississippi, Georgia, and Alabama. That said, the prices of solar are only cheaper in these states because of government subsidies, up to this point at least.
Interesting point: As wind & solar builds up capacity, it gains further economy-of-scale and gets cheaper. The reverse is true for coal & gas, as renewables gain traction, more coal & gas capacity sits idle and the more expensive coal & gas energy gets.