Nearly 70 percent of the energy produced in the United States each year is wasted as heat. Much of that heat is less than 100 °C and emanates from things like computers, cars, or large industrial processes. A thin-film system was developed that can be applied to sources of waste heat like these to produce energy at levels unprecedented for this kind of technology.
The thin-film system uses a process called pyroelectric energy conversion that is well suited for tapping into waste-heat energy supplies below 100 °C, or low-quality waste heat. Pyroelectric energy conversion, like many systems that turn heat into energy, works best using thermodynamic cycles, similar to how a car engine works. But unlike a car engine, pyroelectric energy conversion can be realized entirely in the solid state with no moving parts as it turns waste heat into electricity.
This nanoscopic thin-film technology might be particularly attractive for installing on and harvesting waste heat from high-speed electronics but could have a large scope of applications. For fluctuating heat sources, the thin film can turn waste heat into usable energy with higher energy density (1.06 Joules per cubic centimeter), power density (526 Watts per cubic centimeter), and efficiency levels (19 percent of Carnot efficiency, which is the standard unit of measurement for the efficiency of a heat engine) than other forms of pyro-electric energy conversion.
Thin-film versions of materials 50-100 nanometers thick were synthesized. The pyroelectric-device structures based on these films were fabricated and tested. These structures allow simultaneous measurement of temperature and electrical currents created, and source heat to test the device’s power generation capabilities — all on a film that is less than 100 nanometers thick.