A cooling system powered directly by heat rather than an electric motor has worked in laboratory tests, offering a possible way to turn waste heat or solar energy into cooling. The prototype, developed by researchers at Karlsruhe Institute of Technology (KIT) and the University of Tsukuba, uses two ultrathin nickel-titanium films that convert heat first into mechanical motion and then into cold.

The concept addresses a limitation of elastocaloric cooling, an emerging solid-state alternative to conventional refrigeration. Shape-memory alloys cool when a mechanical load applied to them is released, but existing elastocaloric systems still need electrically powered actuators to supply that force. The new design instead uses heat itself to drive the process.

That distinction matters because cooling and heating account for almost half of global energy consumption as demand continues to grow. Conventional refrigerators, air conditioners, and data centers have relied for more than a century on electricity-driven compressors that move heat with refrigerants, many of which also contribute to global warming.

Heat replaces the electric actuator
The system pairs two nickel-titanium films with different jobs. When heated, the first film shrinks through a shape-memory effect, converting thermal energy directly into mechanical work without an electric motor.

That movement acts on the second film. Repeated loading and unloading cause reversible changes in its crystal structure that produce cooling. In effect, the first film replaces the electrically driven actuator that elastocaloric systems have previously required...