Hybrid Thermoelectric–Photovoltaic Generators under Negative Illumination Conditions

Bruno Lorenzi

doi:10.1021/acsaem.1c02710

Abstract

This paper analyses the working principles of hybrid thermoelectric photovoltaic generators under negative illumination (also referred to as thermoradiative configuration). These kinds of systems combine a thermoradiative photovoltaic cell (TR-PV cell) and a thermoelectric generator (TEG), placed in thermal contact with each other. In this configuration, the TR-PV part cools while irradiating toward the cold sky. For this reason, in addition to the generation of electrical output, the cell can set a difference of temperature (ΔT) across the TEG legs. A theoretical model describing the behavior of these kinds of hybrid devices is reported as a function of the emitter energy gap and temperature, the sky temperature, and the ΔT across the TEG. In analogy with the positive illumination case, the key parameter is found to be the cell temperature sensitivity, which sets the convenience of the hybrid approach. The results show that while the hybrid power density is in general smaller than the sole TR-PV case, a wide window of positive efficiency gains exists. This is possible because the outgoing power density varies with the cell temperature, in contrast with the positive illumination case where the incoming power density is fixed by the temperature of the Sun. This work sets the first theoretical attempt to understand the convenience of TR-hybrid thermoelectric–photovoltaic generators (TR-HTEPVG), quantitatively assessing the suitability of these novel kinds of devices.

Highlights

As renewables are becoming a big role player in satisfying the energy demand, it is clear that their intrinsic intermittent nature is an issue that needs strong efforts to be overcome
Another solution for night generation proposed in the literature consists in the use of the radiative cooling principles applied to thermoelectrics.[16−20] In this case, an optimized emitter is placed in thermal contact with the cold side of a thermoelectric generator (TEG), while the other side is kept at room temperature
As in the positive illumination case, the convenience of thermoelectric hybridization depends on the trade-off between the TR cell efficiency decrease versus temperature and the increase due to the TEG addition

Summary

INTRODUCTION

As renewables are becoming a big role player in satisfying the energy demand (at least in terms of electric energy), it is clear that their intrinsic intermittent nature is an issue that needs strong efforts to be overcome. Exploiting the principle of radiative cooling.[14] In this configuration, a TR cell can produce an ideal output power of 54 W/m2,15 which has been estimated to potentially add a ∼12% contribution to what is produced by a solar cell during the day.[13] Another solution for night generation proposed in the literature consists in the use of the radiative cooling principles applied to thermoelectrics.[16−20] In this case, an optimized emitter is placed in thermal contact with the cold side of a thermoelectric generator (TEG), while the other side is kept at room temperature. This work is a substantial advance in the understanding and the development of effective thermoradiative energy harvesters

WORKING PRINCIPLES

RESULTS AND DISCUSSION

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