In a significant breakthrough for renewable energy storage, researchers at the University of Michigan have developed devices that convert heat into electricity with an impressive 44% efficiency. This development brings practical grid applications closer to reality, marking a substantial step toward efficient energy storage solutions.
Heat batteries, capable of storing excess renewable energy during peak production, utilize a thermal version of solar cells to convert the stored heat into electricity. This method addresses a critical challenge in renewable energy, namely the mismatch between energy generation from solar and wind sources and the actual energy demand. According to Andrej Lenert, Associate Professor of Chemical Engineering at the University of Michigan, achieving decarbonization goals necessitates lower-cost and longer-duration energy storage solutions.
Thermophotovoltaic (TPV) cells, which function similarly to conventional solar cells, are pivotal to this innovation. Unlike photovoltaic cells that convert visible light photons into electricity, TPV cells utilize lower-energy infrared photons. The research team’s new device has achieved a power conversion efficiency of 44% at temperatures as high as 1,435°C, surpassing the previous 37% efficiency mark within the same temperature range.
Stephen Forrest, Professor of Electrical Engineering at the University of Michigan, highlights the benefits of TPV cells. Unlike lithium-ion batteries, which require mining and compete with the electric vehicle market, TPV-based heat batteries offer a passive and versatile storage solution. These heat batteries can be implemented without geographical constraints, unlike hydroelectric energy storage, which requires a water source.
In heat batteries, TPV cells surround a heated material block at temperatures exceeding 1,000°C. This material can be heated using electricity from wind or solar farms or by absorbing excess heat from industrial processes such as steel, glass, or concrete production. The key to the study’s success was optimizing the semiconductor material in the TPV cells to capture a broader range of photon energies, aligning with the dominant energies produced by the heat source.
The researchers addressed the challenge of photon energy mismatch by designing an innovative air bridge structure within the TPV cells. This structure traps photons with the correct energies for conversion and recycles those that initially escape, enhancing overall efficiency. Bosun Roy-Layinde, a chemical engineering doctoral student and the study’s first author, emphasized the advantage of TPV cells over solar cells in their ability to recuperate and recycle photons.
A recent advancement in the design involves stacking two air bridges, further increasing the range of photons converted to electricity and expanding the useful temperature range for heat batteries. Forrest expressed confidence that the efficiency of this technology will soon exceed 44%, potentially reaching 50% shortly.
With patent protection underway through U-M Innovation Partnerships, the research team actively seeks industry partners to commercialize this promising technology. Developing efficient and versatile heat-to-electricity conversion devices represents a significant leap forward in renewable energy storage, promising to play a crucial role in achieving global decarbonization objectives.
This breakthrough positions thermophotovoltaic cells as a viable and scalable solution for integrating higher fractions of renewables into the grid, paving the way for a more sustainable and energy-efficient future.
