Researchers
are working on a thermoelectric generator that converts the heat from
car exhaust fumes into electricity. The module feeds the energy into
the car’s electronic systems. This cuts fuel consumption and helps
reduce the CO2 emissions from motor vehicles.

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In
an age of dwindling natural resources, energy-saving is the order of
the day. However, many technical processes use less than one-third of
the energy they employ. This is particularly true of automobiles, where
two-thirds of the fuel is emitted unused in the form of heat. About 30
percent is lost through the engine block, and a further 30 to 35
percent as exhaust fumes. Scientists all over the world are developing
ways of harnessing the unused waste heat from cars, machines and power
stations, in order to lower their fuel consumption.

There is
clearly a great need for thermoelectric generators, or TEGs for short.
These devices convert heat into electrical energy by making use of a
temperature gradient. The greater the temperature difference, the more
current TEGs can produce. 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 BĂ¶ttner, 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 batterie. 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 BĂ¶ttner.

A simple calculation will illustrate how important
it is to increase the energy efficiency of cars: There are about 50
million licensed motor vehicles in Germany, each of which is — as a
basis for an estimation — on the road for an average of 200 hours a
year. If their waste heat was utilized by TEGs during that time, with
an output of one kilowatt sufficient to power parts of vehicle
electronics, this would add up to ten terawatt hours of energy per
annum — a significant contribution. The researchers are still in the
experimentation phase at present, but they plan to build the first
prototypes very soon.