Thermoelectrics -- which use wasted heat to generate electricity -- could get a lot more interesting thanks to a company called Alphabet Energy. It's set to commercialize tetrahedrite, a metal that more than doubles the efficiency of current tech for as little as a fiftieth the cost. Thermoelectric materials work because they can do a rare trick: transfer heat poorly while conducting electricity well. However, current materials are pricy and polluting, and only convert about 2.5 percent of heat energy to electricity. Tetrahedrite, meanwhile, could reach 5 to 10 percent efficiency while running a mere $4 per kilogram. Alphabet Energy says it could tap waste heat from industrial plants or even a vehicle's exhaust system to produce electricity, making it virtually free. That'd mean you could power your car's cooling AC using wasted heat, ironically -- without a solar panel in sight.