MIT researchers have developed a new technology to harness waste heat. More than 50% of the energy spent globally is wasted, mostly in the form of excess heat.

The new technology will help convert this excess heat dissipated by devices ranging from computer chips to car engines, into electricity with an efficacy much higher than the existing devices.

That kind of waste-energy harvesting might, for example, lead to cellphones with double the talk time, laptops that can function twice as long before needing to be charged.

Theory says that conversion of heat into electricity can never go beyond a precise value known as the Carnot Limit, based on a 19th-century formula for determining the maximum efficiency that any device can attain in converting heat into work.

But current commercial thermoelectric devices only attain about one-tenth of that limit, says Peter Hagelstein, MIT Associate Professor of Electrical Engineering, an MIT release said.

In tests involving a different new technology, thermal diodes, Hagelstein worked with Yan Kucherov, a consultant for the Naval Research Lab, and team to show efficiency as high as 40 percent of the Carnot Limit.

The computations show that this new kind of arrangement could in the end reach as much as 90 percent of that ceiling or nine times as much as current devices.