Research from the University of Michigan indicates that devices for converting heat into electricity are becoming increasingly efficient and may soon become practical for use on the grid. Heat batteries have the potential to store intermittent renewable energy during peak production hours by using thermophotovoltaic cells to convert heat into electricity. As the grid incorporates higher fractions of renewables to meet decarbonization goals, lower costs and longer durations of energy storage are needed to match solar and wind energy generation with when the energy is used.
Thermophotovoltaic cells operate similarly to traditional solar cells, but they utilize lower energy infrared photons rather than visible light photons. The team’s new device has achieved a power conversion efficiency of 44% at 1435°C, surpassing previous designs within the high-temperature energy storage range of 1200°C-1600°C. Heat batteries represent a passive form of energy storage that eliminates the need for mining lithium as with electrochemical cells, making it a more sustainable alternative that does not compete with the electric vehicle market or require a nearby water source like hydroelectric energy storage.
In a heat battery system, thermophotovoltaics would encompass a block of heated material at temperatures exceeding 1000°C, which can be achieved through electricity from renewable sources or by utilizing excess heat from various industrial processes. By engineering an air bridge structure into the thermophotovoltaic cell, researchers were able to optimize the capture of thermal photons and recycle photons that would otherwise be lost, improving the overall efficiency of the system. This innovative design approach has the potential to further increase energy conversion rates and broaden the temperature range for heat batteries.
The researchers are confident that they can continue to improve the efficiency of thermophotovoltaic cells beyond the current 44% rate, with the goal of reaching 50% in the near future. By stacking multiple air bridges in the cell design, they were able to enhance photon conversion and expand the range of useful temperatures for heat batteries. With the assistance of U-M Innovation Partnerships, the team has applied for patent protection and is actively seeking partners to help bring this technology to market, potentially revolutionizing energy storage solutions and grid sustainability.
The study was supported by funding from the National Science Foundation and the Army Research Office, highlighting the importance of continued investment in research and development for advancing clean energy technologies. By harnessing the power of thermophotovoltaic cells and heat batteries, the potential exists to create a more efficient and sustainable energy storage system that can help address the challenges of integrating renewables into the grid and reducing carbon emissions. The ongoing efforts of the University of Michigan researchers demonstrate the potential for cutting-edge technology to drive innovation in the energy sector and accelerate the transition to a more sustainable future.