Efficiency Enhancement of a Thermophotovoltaic System Integrated With a Back Surface Reflector

Abstract

This work aims to investigate the various factors which may affect a thermophotovoltaic (TPV) system's performance, with a special focus on the importance of incorporating a back surface reflector (BSR), which enables below-bandgap photons' recycling. The possible extent to which common PV materials can be used in TPV applications is investigated by comparing them on a Planck distribution curve. The effects of varying BSR reflectivity, TPV cell's external quantum efficiency, and emitter temperature are investigated on the TPV module's efficiency using open-circuit voltage, empirical relations for fill factor, maximum voltage, and photogenerated current. It is shown that TPV applications require materials with smaller (e.g. 0.6 eV < Eg ≤ 0.74 eV) bandgap energy, e.g. In0.53Ga0.47As (0.74 eV), due to their high percentage of energy (> 26%) abovebandgap without a spectral control and a small difference between peak and bandgap wavelength. It is shown that the inclusion of a BSR (reflectivity = 1) results in an increase of 15% in TPV efficiency. The results show that by the collective changes of an added BSR, high emitter temperature (> 2000 K), and improved external quantum efficiency (EQE ≈ 1), the present TPV systems can attain efficiency values more than 30% which makes them a favorable prospective choice for Concentrated Solar Power.

Efficiency Enhancement of Thermophotovoltaic Cells With Different Design Configurations Using Existing Photon Recycling Technologies

“…Wind and solar renewable energy resources are examples of renewable energy resources, but they are not dependable as they depend on weather conditions (Barber, 2018;Jung et al, 2018;Warren et al, 2018;Cendula et al, 2019). However, increased research in the field of renewable energy resources can help overcome this problem (Kazim et al, 2020). Concentrated solar power (CSP) uses focused Sun rays to generate electrical power and is widely used nowadays.…”

“…Concentrated solar power also faces a lot of the irradiation at their surface due to which efficiency is decreased as irradiation is increased (Chen et al, 2016a). We cannot extract photons from the CSP as they cannot be stored for a longer period (Kazim et al, 2020). Thermophotovoltaics (TPVs) can be used in addition to the CSP, as it converts solar radiation to an intermediate form of energy (Boriskina et al, 2015).…”

“…Secondary sources receive the reflected Sun rays from heliostats. The heat transfer fluid (HTF) heats up via the secondary collectors and goes to the thermal energy storage (TES) where it cools down and gets pumped back to repeat the cycle (Kazim et al, 2020). The schematic diagram in Figure 2 shows the energy and temperature conversion of the system in which overall flow chart of Sun rays to electrical output is shown.…”

“…Under high partial shading conditions (PSC), the HTF does not attain a temperature high enough to melt the PCM, now when HTF passes from the TES the PCM releases energy and heats up the HTF. Valves are fitted in the system to maintain the unidirectional flow of the HTF as they prevent the HTF from flowing back to the TES and collectors from the TPV power cycle (Kazim et al, 2020). Many other solar thermal conversion and thermal energy storage of phase change composites materials are used such as CuO/paraffin (Chen et al, 2019).…”

“…On a TPV cell's surface, photons are absorbed, but some quantity of them is lost due to the interference on the surface. BSR is placed behind the TPV cells (Kazim et al, 2020). BSR mounted on the backside of the cell reflects the unabsorbed photons that are passed unabsorbed from the cell back to the active area of the TPV cell for the reabsorption which helps in increased efficiencies (Datas and Vaillon, 2021).…”