MIT turns waste heat into energy
Just about everything that uses electricity heats up. Your desktop computer, your laptop, television, refrigerator, you name it, it produces waste heat. Massachusetts Institute of Technology (MIT) is developing new technology that will convert that excess heat into electricity that can be used to increase the distance electric cars can run, the length of time your laptop can run on its battery, increase the amount of energy generated at power stations and increase your cell phone talk time. MIT has developed a new thermoelectric technology called thermal diodes.
MIT believes that its thermoelectric technology will be able to reach 90 percent of the Carnot Limit.
Theory says that conversion of heat into electricity can never exceed a specific value called the Carnot Limit, based on a 19th-century formula for determining the maximum efficiency that any device can achieve in converting heat into work.
Current thermoelectric technology has only reached 10 percent of the Carnot Limit, but Peter Hagelstein, associate professor of electrical engineering, Yan Kucherov, a consultant for the Naval Research Laboratory, and coworkers have used thermal diode technology to reach 40 percent of the Carnot limit. The teams calculations show that 90 percent of the Carnot Limit is possible with this new technology.
The teams research used a “a single quantum-dot device — a type of semiconductor in which the electrons and holes, which carry the electrical charges in the device, are very tightly confined in all three dimensions.” Normally, there is a tradeoff that has to be made by the current technology. “With present systems it’s possible to efficiently convert heat into electricity, but with very little power. It’s also possible to get plenty of electrical power — what is known as high-throughput power — from a less efficient, and therefore larger and more expensive system.” The new technology used by MIT should allow efficient conversion of heat into electricity with high throughput power. In other words, a smaller less expensive system can accomplish the efficient conversion of heat into plenty of electrical power. Small, efficient, and inexpensive mean that this technology should have a better chance of being a commercial success than current technologies are.
The new technology depends on quantum dot devices, a specialized kind of chip in which charged particles are very narrowly confined to a very small region. Such devices are under development, but still a few years away from commercial availability.
In other words, this technology although promising won’t be available for some years to come. However a company called MTPV Corporation, one of the funding sources for MIT’s research, has similar technology for photovoltaic devices that should be available sooner.
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