Wind is not replacing coal; gas is. Natural gas will need to be burned in gas-fired power plants whether the demand on the grid is high or low and whether or not the wind is blowing. Gas is replacing coal, to be burned to provide base and intermediate load. It also provides load-following and back up to the wind generators because the nuclear plants cannot respond quickly enough, and stored water is a valuable commodity not to be wasted.
This means that when demand is low, expensive wind energy displaces the clean, cheap electricity from the nuclear plants that will have to power down (giving wear and tear concerns) or even shut down, and will not displace the electricity from the polluting and greenhouse- gas-emitting gas-fired plants. More wind makes a bad situation worse.