Nanoscopic film can trap waste heat for useful electrical energy

JP Casey 16 April 2018 (Last Updated April 16th, 2018 17:08)

Scientists from the University of California, Berkeley have developed a nanoscopic film that can be placed on sources of waste heat, such as computers and cars, and produce unprecedented levels of useful energy.

Nanoscopic film can trap waste heat for useful electrical energy
The film produced 1.06 joules per cubic centimetre at 19% efficiency, which are both records for a pyroelectric energy conversion. Credit: Shishir Pandya

Scientists from the University of California, Berkeley have developed a nanoscopic film that can be placed on sources of waste heat, such as computers and cars, and produce unprecedented levels of useful energy.

The group published its findings today in the journal Nature Materials. The thin-film system uses a process called pyroelectric energy conversion, where crystals within the film generate electricity when they are heated. The process is most effective using a thermodynamic cycle, similar to that of a car engine, but it can take place entirely in the solid state, with no moving parts, making the process effective in thin materials such as the prototype developed by the university.

“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,” said senior author and associate professor of materials science and engineering Lane Martin.

“All we’re doing is sourcing heat and applying electric fields to this system, and we can extract energy.”

Martin’s team synthesised thin-film materials just 50-100 nanometres thick, and worked with a group led by Chris Dames, associate professor of mechanical engineering at Berkeley, to produce and test the pyroelectric devices based on these films. The researchers were able to simultaneously measure the temperature and electrical currents created, and source heat to test the device’s power generation capabilities.

The report describes new records for pyroelectric energy conversion: energy density of 1.06 joules per cubic centimetre, power density at 526 Watts per cubic centimetre, and efficiency at 19% Carnot efficiency.

“We know we need new energy sources, but we also need to do better at utilising the energy we already have,” said Martin.

“These thin films can help us squeeze more energy than we do today out of every source of energy.”

Pyroelectric conversion can take place on heat sources below 100 degrees Celsius, known as low-quality waste heat. Low-quality heat accounts for 60% of unrecovered waste heat, according to ‘Waste Heat Recovery: Technology and Opportunities in US Industry’, a 2008 study by the US Department of Energy.

The researchers from California also report that nearly 70% of the energy produced in the US each year is wasted as heat, and improvements in nanoscopic film technology, particularly the feasibility of measuring the properties of nanoscopic films, has enabled a breakthrough of this nature.

The project was supported in part by grants from the Army Research Office and the National Science Foundation.