Startup Alphabet Energy has its first product: what it says is the world’s largest thermoelectric generator. Power plants waste huge amounts of energy as heat—about 40 to 80 percent of the total in the fuel they burn. A new device could reduce that waste, cutting fuel consumption and carbon emissions by as much as 3 percent and saving companies millions of dollars. (Three percent might not seem like much, but for context, air travel accounts for 2 percent of worldwide carbon dioxide emissions.) The generator makes use of a novel, highly efficient thermoelectric material discovered recently at the University of...