UC San Diego

High temperature thermal design can be utilized for applications such as space exploration, safety, energy, transportation. Energy will become an increasingly significant area of focus due to the rising concern for climate change coupled with an increase in energy consumption. Concentrated solar power (CSP) utilizes sunlight for energy production and has an advantageous thermal energy storage component (TES). Next generation CSP plants aim to reduce LCOE to ≥ $0.05/kWh by 2030, and thermal design solutions are required to help achieve that goal.

The receiver of a CSP plant is responsible for collecting the sunlight reflected from the mirrors in the solar field. Chapter 2 of this dissertation will discuss solar absorber nanoporous films for solar receivers. The nanoporous nature allows for an increased optical path of light, and spinel oxides have high melting point and uniform thermal expansion. The nanoporous spinel oxide films have high solar absorptivity, and the high solar absorptivity is maintained after annealing at elevated temperatures. Chapter 3 and 4 will discuss 3D solar absorber nanoneedle coatings, which demonstrate exceptionally ultra-high solar absorptivity (above 99%). As discussed in Chapter 3, after doping with stable phases and depositing uniform passivation coatings, the nanoneedle coatings demonstrate excellent thermal stability. In Chapter 4, a transparent conductive oxide layer is deposited on top of the nanoneedle which enhances infrared emissivity. While not suitable for CSP applications, broadband absorption could be used for satellites or thermal imaging.

Thermal storage of the heat transfer fluid allows for electricity to be generated after the sun sets. Molten salt is the common heat transfer fluid due to its high heat capacity but has two major flaws: it decomposes below the current target temperature, and the metal pipes and metal storage tanks are susceptible to corrosion. Therefore, a thermally insulating and corrosion resistant layer to coat the inside of storage tanks and pipes could allow for a wide array of new molten salt candidates. In Chapter 5, high entropy ceramics are proposed as the next thermally-insulative corrosion-resistant coating for CSP thermal storage systems due to their severe lattice distortion. Single phase high entropy spinel oxides were fabricated via hydrothermal growth and characterized through energy-dispersive X-ray spectroscopy and X-ray diffraction. After condensing into pellets, their room temperature thermal conductivity was measured and compared to other low-entropy spinel oxides.