The most environmentally friendly are tidal power plants. In fact, they transform the kinetic energy of the change in the Earth's rotation speed, associated with the influence of changes in the positions of the Moon and the Sun relative to the Earth. Theoretically, such power plants should slow down the Earth’s rotation, but the effect will be noticeable, I believe, only in a couple of billion years (when the Sun will gobble up the Earth anyway). Windmills are harmful in themselves because they generate very powerful infrasound - birds and animals around die, and people have all kinds of arrhythmias and problems with internal organs