1TW of energy stored in Germany's exhaust pipes

On cold winter’s days as a youth, Greenbang would stand behind the exhaust pipe of the family car, warming her legs on the hot gas as her dad tried to coax the old banger into a few more miles of life.

In retrospect, it’s easy to see Greenbang as a pioneer of scientific investigation, with her early work taken up by the Fraunhofer Institute for Physical Measurement Techniques IPM. Yes, Greenbang is pleased to say the scientists over there are now looking at how to reclaim energy from the heat in car exhaust, using a new type of thermoelectric generator.

According to the institute, two-thirds of the fuel guzzled by cars is emitted unused in the form of heat, with some 30 percent lost through the engine block, and an extra 30 to 35 percent as exhaust fumes.

Here’s what the scientist are up to:

Researchers at the Fraunhofer Institute for Physical Measurement Techniques IPM are developing thermoelectric materials, modules and systems to harness the residual heat in automobiles. “The temperatures in the exhaust pipe can reach 700 degrees Celsius or more,” says Dr. Harald Böttner, head of the Thermoelectric Systems department.

“The temperature difference between the exhaust pipe and a pipe carrying engine cooling fluid can thus be several hundred degrees Celsius.” The thermoelectric converter makes use of this huge differential: Driven by the flow of heat between the hot exhaust fumes and the cold side of a coolant pipe, the charge carriers pass through special semiconductors, thus producing an electric current similar to a battery.

The long-term objective is to make the alternator superfluous and to supply energy to the constantly rising number of power consumers in the car. TEGs could cover a significant proportion of a car’s power requirements: “This would make it possible to cut gas consumption by between five and seven percent,” says Böttner.

A back of an envelope calculation by the institute reckons if the generators were put on all Germany’s cars, around on terawatt a year could be reclaimed. Nice.