Renewable energy sources like solar and wind power offer a sustainable path forward, but their intermittent nature presents a significant challenge. Researchers at MIT have developed a highly efficient thermophotovoltaic (TPV) cell that could address this issue by efficiently converting stored thermal energy into electricity. This groundbreaking technology has the potential to transform how we store and utilize renewable energy, paving the way for a more reliable and sustainable power grid.
The key to this innovation lies in what MIT mechanical engineer Asegun Henry, author of the new Nature study, refers to as “thermal batteries.” These batteries store energy generated from renewable sources as heat, offering a cost-effective alternative to traditional lithium-ion batteries. Henry explains that storing energy thermally is significantly cheaper, potentially by a factor of 10 to 100, compared to electrochemical storage. This cost advantage makes thermal batteries a promising solution for grid-scale energy storage.
How the Thermophotovoltaic Cell Works
The TPV cell leverages fundamental semiconductor physics to convert photons (light particles) into electricity. The cell consists of layered semiconducting alloys with specific band gaps, the energy difference between an electron’s valence and conduction bands. When photons strike the cell, they energize electrons, causing them to jump across the band gap and release energy. The amount of energy released depends on the size of the band gap, which is carefully engineered in the alloy layers.
This particular TPV cell comprises two semiconducting alloy layers and a reflective gold layer. The first alloy layer has the largest band gap, capturing the highest-energy photons. Photons with insufficient energy for the first layer pass through to the second layer, which has a smaller band gap. The gold layer reflects any remaining low-energy photons back to the light source, minimizing energy waste.
Diagram of the thermophotovoltaic cell showing the layers and photon interaction.The thermophotovoltaic cell features layered alloys and a reflective gold layer to maximize photon capture and energy conversion.
In the lab, the researchers used a superheated metal as the photon source. A resistive heater, similar to a lightbulb filament, heated the metal to extremely high temperatures (between 1,900 and 2,400 degrees Celsius), causing it to emit photons that the TPV cell then captured.
From Lab to Real-World Application: The “Sun-in-a-Box”
The researchers envision a real-world application where renewable energy sources power resistive heaters to heat liquid metal. This heated liquid metal would then be pumped over blocks of graphite, creating a “sun-in-a-box” operating at half the temperature of the Sun. This system would power the resistive heaters, generating the photons needed for the TPV cells, which would be arranged in a large array.
Conceptual illustration of the "sun-in-a-box" system.The “sun-in-a-box” concept utilizes heated liquid metal and graphite blocks to store and release thermal energy.
This concept builds upon previous research by the same team, who achieved a Guinness World Record for pumping liquid metal at temperatures exceeding 1,000 degrees Celsius. While acknowledging the complexities of this system, Henry emphasizes the potential for remote maintenance and safe inspection procedures, even within the inert gas environment required for operation.
A Promising Future for Renewable Energy
The TPV cell developed by the MIT researchers boasts a remarkable 40% efficiency, exceeding previous designs and rivaling traditional steam turbines. This achievement signifies a major step towards scalable, cost-effective thermal energy storage. The team’s next goal is to scale up this technology to create a warehouse-sized power station that can be integrated into the existing power grid. This advancement could revolutionize how we store and utilize renewable energy, ultimately contributing to a cleaner and more sustainable energy future.
