Thermophotovoltaics

Project Title: Multi-scale modeling and design of an efficient thermophotovoltaic system

Project Dates: September 2021 - Present

Collaborators: Minok Park, Kyle Buznitsky, Alina LaPotin, Ashwin Sandeep, Santosh Shanbhogue, Colin Kelsall, Vasillia Zorba, Ahmed Ghoniem

Location: Atomistic Simulation & Energy Research Group, Massachusetts Institute of Technology

Project Summary:

Thermophotovoltaics use the same technology as solar photovoltaics, but instead of using the sun as the light source, they use a glowing hot object. TPV cells convert the light emitted from the hot object into electricity. This offers 3 main benefits. First is reliability, as the operator has full control over the light source. Second is efficiency, as TPV cells can reflect unused light back to the emitter, unlike solar cells which lose this energy. Third is power density, as the light intensity hitting TPV cells can be much higher than sunlight, allowing for more power generation per unit area.

Despite these advantages, TPVs have not yet seen broad adoption. To answer why, I first developed a techno-economic framework to evaluate the cost of electricity produced by TPV cells. I found that if certain performance metrics are met (efficiency of 50%, power density of 5 W/cm2, heating cost of 5 cents/kWh, and cell cost of 5 $/cm2), TPV's (levelized) cost of electricity can be competitive with conventional sources (at around 8 cents/kWh). While other works have focused on increasing efficiency and reducing cell cost, power density and heating cost have been underexplored.

How can we maximize power output from TPV cells? There are a variety of levers to pull, including emitter temperature, emitter emissivity, emitter-cell view factor, and cell bandgap. Of these, emitter emissivity is the most versatile and broadly tunable. Therefore, I developed an emitter engineering technique based on laser ablation that is applicable across a wide variety of high-temperature materials including refractory metals, nickel superalloys, and carbides. In collaboration with LBNL, I demonstrated this emitter retains near-unity emissivity around the TPV bandgap even after heating to 2000C for 100 hours, and can double TPV power density compared to a plain emitter.

Next, how can we minimize heating cost? One promising approach is to use ammonia as a fuel, which is liquid at moderate pressures and therefore can be easily stored and transported. In collaboration with the Reacting Gas Dynamics lab at MIT, I designed and demonstrated a next-generation power plant that uses ammonia combustion to generate heat for TPV cells. In a recent demonstration, we achieved high TPV power density (2 W/cm2) and low NOx (~20 ppm), critical for commercialization of ammonia as a fuel.

With these innovations, TPVs are poised to become a key technology for decarbonizing the energy sector, with applications in power generation, heavy-duty transportation, and beyond.