Abstract

We present a systematic optimization of nighttime thermoelectric power generation system utilizing radiative cooling. We show that an electrical power density >2 W/m2, two orders of magnitude higher than the previously reported experimental result, is achievable using existing technologies. This system combines radiative cooling and thermoelectric power generation and operates at night when solar energy harvesting is unavailable. The thermoelectric power generator (TEG) itself covers less than 1 percent of the system footprint area when achieving this optimal power generation, showing economic feasibility. We study the influence of emissivity spectra, thermal convection, thermoelectric figure of merit and the area ratio between the TEG and the radiative cooler on the power generation performance. We optimize the thermal radiation emitter attached to the cold side and propose practical material implementation. The importance of the optimal emitter is elucidated by the gain of 153% in power density compared to regular blackbody emitters.

Highlights

  • The rapid growth of world population and industrial development poses a major threat to the global energy supply, causing escalatory environmental degradation and social unrest [1,2,3]

  • A proof-of-concept experiment [9] developed a device that couples the cold side of a thermoelectric power generator (TEG) to a sky-facing blackbody surface that radiates heat to the cold of space and has its hot side heated by the surrounding air, enabling electrical power generation of 25 mW/m2 at night

  • For all three cases the maximum power density is achieved with the TEG area less than 1 percent of the radiative cooler area

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Summary

Introduction

The rapid growth of world population and industrial development poses a major threat to the global energy supply, causing escalatory environmental degradation and social unrest [1,2,3]. With typical temperature difference between the ambient and hot side of few degrees K and the free air convection coefficient of 8∼10 W/m2K [9], the input power density provided to the generator is limited to on the order of 10 W/m2 - which, with the typical power conversion efficiency of TEG, cannot provide the desired 1 W/m2 power density, requiring significant enhancement A proof-of-concept experiment [9] developed a device that couples the cold side of a TEG to a sky-facing blackbody surface that radiates heat to the cold of space and has its hot side heated by the surrounding air, enabling electrical power generation of 25 mW/m2 at night This demonstration of nighttime electrical power generation is remarkable, it is not sufficient to fulfill energy demand of many applications mentioned above.

Analysis of nighttime thermoelectric power generation
Optimization of the radiative cooler emissivity
Parameter influence on the system performance
Thermodynamic limit of power generation at night
Findings
Concluding remarks

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