Federal support might turn green energy companies suddenly profitable, but after decades of losses, you should be skeptical of that.Renewable energy stocks surged higher Tuesday after Plug Power (PLUG 20.24%) announced receipt of a $1.66 billion loan guarantee from the U.S. Department of Energy. Plug currently has two hydrogen fuel facilities producing at full capacity, with a third approaching that mark. Plug says the government assistance will help it to "finance the development, construction, and ownersh ...