Green Energy

As I understand it, the reason sheep are so good is that they don't graze up, so they're unlikely to try munching on any power cords (unlike goats). I don't know enough about cows to say definitively, but my guess is that you're going to need the solar panels up high enough for them to be comfortable, and also sturdy enough that a leaning cow won't knock them over. So it may work but the additional considerations could prove more expensive.