Thin films squeeze more energy from waste heat

Thin films squeeze more energy from waste heat

Technology News |
Researchers at the University of California, Berkeley have developed a thin-film system that can be used with sources of waste heat - such as computers, cars, or industrial processes - to produce energy at levels said to be unprecedented for this kind of technology.
By Rich Pell


The researchers’ thin-film system uses pyroelectric energy conversion – a process well suited for tapping into waste-heat energy supplies below 100°C, i,e, “low-grade” waste heat. Working with thermodynamic cycles, pyroelectric energy conversion can be realized using no moving parts as it turns waste heat into electricity.

According to the researchers, while their nanoscopic thin-film technology may be particularly suited for installing on and harvesting waste heat from high-speed electronics, it could have a large scope of applications. For fluctuating heat sources, they say, the thin film can turn waste heat into usable energy with higher energy density, power density, and efficiency levels than other forms of pyroelectric energy conversion.

“We know we need new energy sources, but we also need to do better at utilizing the energy we already have,” says Lane Martin, associate professor of materials science and engineering at UC Berkeley and lead author of a study on the research. “These thin films can help us squeeze more energy than we do today out of every source of energy.”

While pyroelectric behavior has been understood for a long time, accurately measuring the properties of thin-film versions of pyroelectric systems has remained a challenge. This new research is said to help demystify that process and improve the understanding of pyroelectric physics.

The researchers began by synthesizing thin-film versions of materials of 50 to 100 nanometers thick. They then fabricated and tested pyroelectric-device structures based on these films, allowing engineers to simultaneously measure the temperature and electrical currents created, and source heat to test the device’s power generation capabilities.

“By creating a thin-film device, we can get the heat into and out of this system quickly, allowing us to access pyroelectric power at unprecedented levels for heat sources that fluctuate over time,” Martin says. “All we’re doing is sourcing heat and applying electric fields to this system, and we can extract energy.”

The researchers report new records for pyroelectric energy conversion energy density (1.06 Joules per cubic centimeter), power density (526 Watts per cubic centimeter) and efficiency (19% of Carnot efficiency – the standard unit of measurement for the efficiency of a heat engine). The next steps, say the researchers, will be to better optimize the thin-film materials to specific waste heat streams and temperatures.

“Part of what we’re trying to do,” says Martin, “is create a protocol that allows us to push the extremes of pyroelectric materials so that you can give me a waste-heat stream and I can get you a material optimized to address your problems.”

For more, see “Pyroelectric energy conversion with large energy and power density in relaxor ferroelectric thin films.”

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