It checks for obstructions all around it (rather than just the front), so if nearly half the blocks are obstructions it's not going to get enough wind to turn.
Thanks a lot, after about moving it about 10~15 blocks forward it started to work. That is not very clear or explained anywhere I've seen, and I think that mechanic could be rethinked, it obligates you to put the generator in mid air, aesthetically not ideal.