Projects to use the remaining sites would run into strong local opposition. Even smaller hydroelectric plants cause some damage to the landscape. With output proportional to wind speed, wind turbines only make sense in coastal areas and on high ridges. Wind is not a constant energy source, so wind energy supplements rather than replaces fossil or nuclear sources. Unsightly and noisy.
Cost is exceptionally high, although prices are starting to come down.
They require a large surface area and high-capacity plants would only be viable in southern Europe. It is renewable and is not dependent on fossil fuels. Gases produced could be used in combined-cycle plants. Surrounding forests can act as sinks for CO2 emissions. Burning biomass creates polluting gases and liquid waste.