Record nighttime electric power generation at a density of 350 mW/m$^2$ via radiative cooling

TL;DR

This paper demonstrates a radiative cooling system that harvests ambient thermal radiation to generate renewable electricity at 350 mW/m², approaching thermodynamic limits, and achieves higher power densities with additional heat sources.

Contribution

The study introduces an optimized design for radiative cooling energy harvesting that significantly increases power density, nearing theoretical thermodynamic limits.

Findings

Achieved 350 mW/m² power density from ambient radiative cooling.

Demonstrated potential to reach 1000 mW/m² with supplementary heat sources.

Approached the thermodynamic upper limit for power density in radiative cooling systems.

Abstract

The coldness of the universe is a thermodynamic resource that has largely remained untapped for renewable energy generation. Recently, a growing interest in this area has led to a number of studies with the aim to realize the potential of tapping this vast resource for energy generation. While the theoretical calculation based on thermodynamic principles places an upper limit in the power density at the level of 6000 mW/m$^2$, most experimental demonstrations so far result in much lower power density at the level of tens of mW/m$^2$. Here we demonstrate, through design optimization involving the tailoring of the thermal radiation spectrum, the minimization of parasitic heat leakage, and the maximum conversion of heat to electricity, an energy generation system harvesting electricity from the thermal radiation of the ambient heat to the cold universe that achieves a sustained power density of 350 mW/m$^2$. We further demonstrate a power density at the 1000 mW/m$^2$ level using an additional heat source or heat storage that provides access to heat at a temperature above ambient. Our work here shows that the coldness of the universe can be harvested to generate renewable energy at the power density level that approaches the established bound.