One problem with wind energy as a major source of electricity is

The right answer to this question is: It needs a very big investment and it's not as efficient as it needs to be.

Explanation:

    Wind generators are usually made out of really expensive metal parts, and need to be pretty efficient too. With the money invested on it, it's pretty much possible to acquire another source of energy and too, more efficient, but this is only one problem.

      Wind energy causes a very big problem to birds and other kinds of flying animals, they die on it simply by flying to it, and that can modify a whole ecosystem, once these birds are a very big part of the food chain. Wind energy is a very good source of energy, and it could be used, but not as a main source of energy.