The loss is enormous: on average, less than one-third of the energy produced by an automobile engine is used to turn the wheels. The rest of it dissipates in the form of heat, particularly exhaust gas. The same goes for energy use in most industries and in the home. According to estimates, between 50% and 70% of the primary energy used worldwide is released as heat into the environment.
Could we benefit from tapping into this underutilized resource and reduce waste? That is the hope motivating Raphael St-Gelais, a professor in the Department of Mechanical Engineering, whose lab received a grant from the New Frontiers in Research Fund in June 2020.
The project’s underlying goal is straightforward: to convert thermal radiation, or heat, directly into electricity using a thermophotovoltaic device. In this case, instead of capturing sunlight, photovoltaic cells are used to recover infrared radiation emitted by warm objects to produce an electric current.
But to do so efficiently, the scientists must place the heat source in very close proximity to the photovoltaic sensor — less than 100 nanometres! In terms of newsworthy benchmarks, that corresponds to the diameter of a coronavirus…
“In very close proximity, certain phenomena amplify the energy transfer,” explains St‑Gelais. The amplification factor can be up to 1,000 times more powerful than in a larger-scale situation. Consider that, in the realm of the infinitely small, certain classic laws of physics no longer apply, and surprising properties emerge.
“The near-field heat transfer mechanism was first observed quite recently. This research area is booming! So now that we know the phenomenon exists, our goal is to show that we can obtain a high level of conversion efficiency,” he adds. To demonstrate that point, St‑Gelais has teamed up with Karin Hinzer, vice-dean, research in the Faculty of Engineering and a solar cell specialist, who will aim to develop photovoltaic cells optimized for those specific wavelengths, and Alejandro W. Rodriguez, a specialist in radiation simulation systems at Princeton University in New Jersey, who will provide theoretical support.
Meanwhile, St-Gelais will design the prototype. “It looks simple but keeping two objects a few nanometres apart without coming into contact with each other is quite a challenge,” he says.
The team is looking to develop cellphone-sized portable devices that could be placed in contact with various heat sources. “Applications are still a long way off, but the devices could function on any surfaces hotter than 600°C, which are common in a number of heavy industries, such as in the aluminum or transportation sectors,” explains St-Gelais.
In the age of climate change, what could be more important than recycling lost heat? It is an ambitious undertaking, but well worth the wager as it could blaze a trail to a novel energy source.