Tailoring Optical and Thermal Properties of Nanostructured Materials for Passive Radiative Cooling

Passive radiative cooling has emerged as a promising way to reduce the amount of primary energy used for cooling. Specifically, cities could use passive radiative cooling to mitigate both urban heat island issues and electricity demand for air conditioning, which accounts for about 10% of electricity use in the U.S. according to the EIA. Decreasing energy consumption also plays an essential role in addressing global warming. For example, retrofitting 80% of commercial roofs in the U.S. could potentially reduce annual energy use by greater than 10 TWh and offset CO2 emissions by about 6 Mt. “Passive radiative” refers to the concept of selectively emitting thermal radiation to Space through the “atmospheric window” (i.e., 8 – 13 µm) without the input of energy. Low atmospheric absorption (high transmission) in this wavelength band allows objects to directly radiate heat to outer space. This effectively uses Space (~3 Kelvin) as a heat sink, which enables sub-ambient cooling. For example, nighttime cooling is a common phenomenon for high emitting materials. On the other hand, daytime cooling is particularly challenging because solar heating on Earth is ~10 times greater than the heat emitted to outer space, but by designing materials to reflect sunlight and emit in the infrared, sub-ambient cooling during peak solar hours is achievable. This dissertation includes a discussion on t…