Design Challenges for Ultra-High-Temperature Energy Storage with Thermophotovoltaics

Abstract

Decarbonization of the electricity grid is an important part of mitigating the extent and effects of human-caused climate change. Some of the most promising carbon-free and renewable energy resources, like wind and solar, have intermittent production that could be addressed, in part, with widespread deployment of electrical energy storage. There are few storage technologies, however, that are suited to this task, partially due to their high cost, rare constituent materials, and geographic constraints. This thesis investigates several pressing design challenges for a new electrical energy storage technology, termed Thermal Energy Grid Storage (TEGS), with the potential for low cost and deployment at scale. TEGS stores electricity as heat in graphite blocks at ultra-high temperatures (>2000°C) and can extract that heat as electricity, on demand, using a thermophotovoltaic (TPV) heat engine. Thermophotovoltaic systems convert thermally emitted light from a high-temperature heat source to electricity using a photovoltaic cell. By operating at extremely high temperatures and utilizing multi-junction PV cells typically intended for solar energy conversion, high conversion efficiencies can be achieved (i.e. > 50%) at low cost. When operating at such high temperatures, however, sublimation of the thermal emitter material (i.e. tungsten) and deposition on the cell surface can cause significant performance degradation. To prevent this contamination process, a layer of gas can be blown across the cell, effectively sweeping the evaporated material away before it gets to the surface. This thesis examines the relevant design parameters of this Sweeping Noble Gas Curtain (SNGC) system with the goal of developing a functional and scalable TPV generator for implementation in the TEGS ultra-high-temperature thermal battery. This work consists of several analytical and numerical models predicting deposition behavior under different geometric and flow conditions, experimental validation of these models, a scalable design for an integrated SNGC-TPV system, a summary of the numerous challenges and solutions devised for testing this system above 2000°C, and finally a proof-of-concept demonstration showing the remarkable efficacy of the SNGC approach. The demonstrated long-term durability enhancement of thermophotovoltaic devices is a critical step towards the economic viability of such systems and their potential for deployment at scale.