A Pragmatic Bilayer Selective Emitter for Efficient Radiative Cooling under Direct Sunlight

Area of Science:

• Materials Science
• Nanotechnology
• Thermodynamics

Background:

• Radiative cooling enables passive temperature reduction without external energy input.
• Photonic crystals and metamaterials offer high-efficiency selective emitters but are costly.
• Developing cost-effective selective emitters is crucial for practical radiative cooling applications.

Purpose of the Study:

• To develop an efficient and cost-effective bilayer selective emitter for radiative cooling.
• To investigate the potential of functional nanoparticles for controlling infrared emission spectra.
• To evaluate the cooling performance of the developed emitter under various conditions.

Main Methods:

• Fabrication of a bilayer selective emitter using functional nanoparticles.
• Optimization of nanoparticle volume fraction to tune spectral emissivity.
• Theoretical calculation of cooling potential.
• Experimental validation through rooftop measurements under direct sunlight.

Main Results:

• The bilayer selective emitter theoretically achieves cooling of 36.7 °C (nighttime) and 25.5 °C (daytime) below ambient temperature.
• Cooling performance is comparable to high-cost photonic crystal and metamaterial emitters.
• Rooftop measurements confirm effectiveness in ambient air, even under direct sunlight.

Conclusions:

• The nanoparticle-based bilayer selective emitter offers an efficient and low-cost solution for radiative cooling.
• The material design demonstrates significant potential for practical, large-scale cooling applications.
• This approach overcomes the cost limitations associated with traditional photonic materials.