Radiative-cooling-based nighttime electricity generation with power density exceeding 100 mW/m²

Area of Science:

• Thermodynamics
• Radiative Cooling
• Energy Harvesting

Background:

• Outer space at 3 K is a thermodynamic resource.
• Nighttime radiative cooling utilizes sky-facing emitters within the 8-13 μm atmospheric transparency window to achieve sub-ambient temperatures.
• Thermoelectric generators (TEGs) have been employed to convert this temperature difference into electricity, but parasitic thermal losses limit power density.

Purpose of the Study:

• To reduce parasitic thermal losses in nighttime radiative cooling systems.
• To optimize power density by engineering the relationship between emitter area and TEG thermal resistance.
• To demonstrate enhanced electricity generation using stacked TEGs.

Main Methods:

• Development of a simple thermodynamic model to identify optimal power density conditions.
• Experimental validation using a sky-facing thermal emitter and thermoelectric generators.
• Implementation of stacked thermoelectric generator configurations to minimize thermal losses.

Main Results:

• Parasitic thermal losses can be significantly reduced through targeted thermal engineering.
• A model demonstrates that optimizing the emitter area to thermal resistance ratio approaches maximum power density.
• Stacking multiple thermoelectric generators effectively minimizes thermal losses.
• Experimental demonstration of an electric power density exceeding 100 mW/m², a >2-fold increase over prior work.

Conclusions:

• Thermal engineering is crucial for improving the efficiency of radiative cooling energy harvesting.
• Optimized system design, including emitter area and TEG configuration, is key to maximizing power output.
• The demonstrated power density represents a substantial advancement in harnessing radiative cooling for electricity generation.