I was a physics major here. There's no such thing as a free lunch when it comes to energy production. There is a concept called energy density where mechanically generally energy will always be less efficient than chemical energy, which, in turn will always be less efficient...

than nuclear. Each poses it's own problems in terms of space used and pollution. Mechanical energy (wind, hydro) because it is so inefficient always requires more infrastructure & disrupts more wildlife habit than any other form of energy production.

A downside of mechanical energy is that it is dependent on weather and almost always requires active backup by chemical energy.