I'm definitely against it, as "alternative energies" by themselves is (to me at least) a somewhat politically charged term (the "good new oppressed" against the "bad, old, traditional"). So in order to be classified as "alternative", you'd have to get a kind of grassroots approval or something, while in fact we are talking about different energy technologies. To see the silliness in this proposal, look at wind energy, it is one of the oldest forms of energy usage by humankind (sail boats, wind mills), but it is "alternative". Nuclear usually doesn't qualify for the grassroots label, although it is one of the newest forms of energy production by humankind.
Usually it is understood to be essentially wind and solar and maybe biofuels, so as others pointed out, general engineering can be suited for that, unless the subject addressed is more specific, such as materials or mechanical engineering for instance in wind energy, or some or other aspect of solar or... If it gets down to the physical principles, the physics section can be used.