Hybrid Thermoelectric–Photovoltaic Generators under Negative Illumination Conditions

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.