Solar/wind is the cheapest form of power generation by far. You just can't beat it because they don't have any fuel costs. Gas peaker plants will always make sense until we have enough grid scale batteries. They will hold on for now until the price of natural gas hits rock bottom. But with the current advances in low cost battery technology I see them becoming less and less necessary. They would probably already be dead if hydrofracturing hadn't propped up the cost of gas.
https://en.wikipedia.org/wiki/Cost_of_electricity_by_source