If you don‘t want to freeze in your electric car, you have to make a few concessions, because heating devours substantial power. Fraunhofer researchers have developed a highly energy-efficient heating system for electric cars, using a coated film that employs carbon nanotubes to produce a broad, radiant heat.

Electric car drivers love the summer, because in the winter, the vehicle’s range declines markedly due to the additional energy demanded by the heating system. Electric cars generate next to no heat compared with conventional passenger vehicles, which produce more than enough engine heat to warm the interior. Electric cars therefore require an additional electric heater, powered by the same battery that provides the engine with energy.

“In the most unfavourable case, you can only drive half the usual distance with the car”, says Serhat Sahakalkan, Project Manager at the Fraunhofer Institute for Manufacturing Engineering and Automation IPA in Stuttgart, Germany.

Researchers at the IPA have now developed a film-based panel heater, which quickly provides a comfortable warmth in electric cars more effectively than electric heaters – particularly on short journeys. The heating concept is based on a film that is coated with conductive carbon nanotubes (CNTs). For this, the researchers spray on a very thin layer of CNT dispersion.

“The film is glued to the inner door trim and generates a comfortable warmth there in the area of the armrest within a very short time,” explains Sahakalkan.

The heater functions in accordance with the Joule principle: when electricity flows through the film, it comes across a natural resistance between the individual nanoparticles. These ‘collisions’ generate heat.

Conventional electric resistance heaters of the type used in electric cars also make use of this principle. Usually, the conductive material used is copper wire, which is embedded in silicone mats, for example. The solution of the researchers from Stuttgart, however, offers several advantages.

While the copper wire heaters available at present are relatively bulky, the film heater consists of a layer of conductive material with a thickness of only a few micrometres. It can be flexibly applied to a wide variety of surfaces, and saves energy and cost due to its low weight. The CNTs themselves have a low heat storage capacity, as a result of which the generated heat is directly released into the environment. As opposed to the wire-based variant, the heat is evenly distributed over the entire surface of the film, which considerably increases efficiency. When the driver switches the heating off, the material cools down just as quickly.

“These fast response times are ideal for short distances such as urban trips”, explains Sahakalkan.

The desired heating output can be infinitely adjusted by the user. Even isolated defects do not impair functionality. In wire-based heating systems, for example, even minor breaks in the metal can lead to failure.

In order to evenly apply the film to the arched door trim, the researchers divide it into small modules and then glue them to the door trim in sections.

“Slight creases arise at the curvatures, which change the spacing of the electrodes,” Sahakalkan states. “Even heat distribution would then no longer be ensured.”

The researchers intend to further simplify the procedure and spray the CNT dispersion directly onto the corresponding vehicle components.

“This would make the production process considerably more economical – particularly in comparison to wire-based solutions,” Sahakalkan says.