Abstract
Based on the photovoltaic effect to produce electricity, thermophotovoltaics (TPV) is quite similar to solar photovoltaics (PV), but with some notable differences. While the latter technology is well established, the development of the former faces specific challenges, but has recently benefited from strong advances and new opportunities. This new momentum is linked to the development of solar-to-heat-to-power (usually called Solar TPV) converters and more recently of power-to-heat-to-power converters. In both cases, a key point is that energy can be efficiently stored under the form of heat, thus allowing to alleviate the intermittency of solar and wind power generation. The storage of latent or sensible heat at ultra-high temperature (1000 to 2400 °C), at high density and low cost [1], is the backbone of the advent of the so-called TPV "batteries" [2] (see e.g. the example of Fig. 1). To start with, the presentation will provide the basic principles of thermophotovoltaics [3, 4]. The differences of TPV conversion with respect to solar PV conversion (Fig. 2) will be described, by highlighting some advantages (tuning of the spectrum of the thermal radiation emitter, photon recycling toward the emitter, increased power density) and some drawbacks (primary energy conversion and heat losses). Then the most promising applications envisioned as part of the transition to carbon-free renewable electricity generation will be introduced. It will be explained how the concomitant development of low-cost thermal energy storage [1] and highly-efficient (> 40%) thermophotovoltaic cells [5] is currently accelerating research on power-to-heat-to-power and solar-to-heat-to-power TPV batteries. Then, an analysis of the state-of-the-art of TPV devices developed and characterized in a laboratory-setting will be proposed. It will be shown that there is a relation between optimum operating temperature of the thermal radiation emitter and bandgap of the photovoltaic cell. The presentation will conclude with a short introduction to advanced concepts, research pathways and associated challenges, and networking initiatives [6] to continue to advance the field.[1] A. Datas, Ultra high temperature thermal energy storage for dispatchable power generation, Encyclopedia of Energy Storage 2, 141-150, 2022.[2] A. Datas et al., Latent heat thermophotovoltaic batteries, Joule 6, 418-443, 2022.[3] T. Burger et al., Present efficiencies and future opportunities in thermophotovoltaics, Joule 4, 1660-1680, 2020.[4] A. Datas & R. Vaillon, Thermophotovoltaic energy conversion, Chapter 11 in: Ultra-High Temperature Thermal Energy Storage, Transfer and Conversion, Woodhead Publishing, 285-308, 2021.[5] A. LaPotin et al., Thermophotovoltaic efficiency of 40%, Nature 604.7905, 287-291, 2022.[6] Team-project TREE: https://tree.ies.umontpellier.fr; iTPV network: https://itpv.ies.umontpellier.fr. Last access on 03/22/2023.