The need for sustainable energy is reaching critical proportions. Current fuel sources release harmful greenhouse gases, and they will eventually run out. Alternative energy sources (such as wind or solar) have come a long way, but they are unlikely to meet energy demands in the foreseeable future. Even when homes get to a zero-emission point, it is important to note the sheer amount of energy consumed for industrial use. Large manufacturing plants can gulp as much energy as entire cities or even some countries.