Research led by Michigan Chemical Engineering PhD student Bosun Roy-Layinde and recent graduate Tobias Burger demonstrates how a unique thermophotovoltaic (TPV) conversion property including an infrared-transparent cell could improve power generation with the use of waste, solar and nuclear heat.
“Overall, our work shows that this approach may expand the use of TPVs into a wider range of applications,” Roy-Layinde said. “This approach also shows significant potential to reduce greenhouse gas emissions.”
Findings represent an 8% absolute improvement in efficiency relative to the best TPV devices at such low temperatures. By enabling near-zero photon loss, the semitransparent architecture facilitates high TPV efficiencies over a wide range of applications.
In particular, the cement, chemical, iron and steel industries represent a large fraction of global industrial energy use and emissions with substantial waste heat streams at temperatures ranging from 700 to 1100°C.
Still, at temperatures compatible with the utilization of waste, solar, and nuclear heat, TPV efficiencies remain relatively low.
This inefficiency is due to a red-shifted emission spectrum, which increases the fraction of heat transferred to the photovoltaic cell by low-energy photons.
In the study, researchers demonstrated an infrared-transparent cell that uses a secondary thermal emitter, to capture more than 99% of these photons.
“To recover some of the energy lost, we can pass these waste heat streams through an emitter that produces infrared radiation,” Roy-Layinde said. “We can then convert the radiation from the emitter back to electrical power using TPV cells.”
Utilizing the concept of transmissive spectral control, the team was able to allow undesired photons to transmit through the cell to be absorbed by a secondary emitter. The fabricated TPV cell consists of a thin membrane supported by an infrared-transparent heat-conducting substrate.
The architecture leverages a unique property of TPVs: the cell can be surrounded by radiation sources. Experiments show TPV efficiencies of 32% at approximately 1000°C and additional modeling suggests 45% is possible even at approximately 800°C.
TPV conversion offers a promising solid-state alternative to mechanical heat engines. Applications of TPV cells in stationary energy storage can support emitter temperatures as high as 2400°C using thermal batteries. However, a wide range of thermal sources are at temperatures below 1100°C, including waste, concentrating solar and nuclear heat, leaving substantial potential for improving TPV conversion.