A host of companies have proposed devices for harvesting the tremendous amount of energy lost as waste heat in factories or even cars.
A breakthrough at MIT may allow engineers to one day harvest the heat inside of laptops and cell phones.
MIT's Peter Hagelstein and Yan Kucherov of the Naval Research Laboratory, conducted an experiment with quantum dots, a type of semiconductor in which positive and electrical charges are confined tightly in all three dimensions, that can convert far more heat into work (i.e., electrical power) than conventional devices. The ability to transform heat into power is measured by the Carnot Limit, which lays out a maximum of how much heat can ultimately be converted. Conventional thermoelectric devices perform at about 10 percent of the Carnot limit. Hagelstein and Kucherov's quantum dot device can go up to 40 percent. Theoretically, it could go up to 90 percent.
Ideally, that means that the device could convert far more heat into work that conventional devices and/or that it could be used in low-temperature settings. If such devices could ever be made commercially, they could double talk time on cell phones or run times in laptops.
You probably don't know it, but you live in the dawn of the Golden Age for waste heat research. The U.S. consumes around 100 quads (100 quadrillion BTUs) of energy a year and 55 to 60 quads get dissipated as waste heat, according to Arun Majumdar, the UC Berkeley professor who now runs ARPA-E, the advanced projects group inside the Department of Energy.
Alphabet Energy, a Lawrence Berkeley National Labs spin-out that was a runner up at the Cleantech Open, says it can make devices that will produce power at close to $1 a watt. Traditional waste heat converters cost around $20 a watt and are made out of bismuth telluride. Alphabet won't say what it's semiconductor is made from, but sources say it is silicon nanowires. Majumdar did some of the original research on Alphabet.
GMZ Energy, Promethean Power and Cypress Semiconductor are all also experimenting with thermoelectric devices and various semi materials like gallium. GMZ and Cypress want to turn heat into power while Promethean converts electricity from PV panels directly into heat.
MC10 and Photonic Devices recently received grants from ARPA-E to develop, respectively, waste heat semiconductors from silicon nanotubes and what silicon nanowires. Nanotubes and nanowires can similarly confine charges and particles by tight dimensions. Carbon nanotubes, for instance, are said to have "ballistic" conductivity because once an electron is inside a tube, it can't scatter or get lost.
Companies such as Recycled Energy Development (RED) and Ormat have successfully retrofitted factories to capture waste heat, but they largely rely on mechanical engineering. Heat is captured and then channeled into productive uses. One of RED's showcase projects coming next year is a system at West Virginia Alloys, a silicon manufacturer, that will generate 45 megawatts of electrical power from the waste heat generated by factory operations. The company uses 120 megawatts right now: The waste heat system will effectively allow Alloys to recover about one-third of the power it now buys but wastes.
Replacing mechanical systems with semiconductors, potentially, will be the next wave for the industry.