Night time performance of a storage integrated solar thermophotovoltaic (SISTPV) system

Abstract

Energy storage at low maintenance cost is one of the key challenges for generating electricity from the solar energy. This paper presents the theoretical analysis (verified by CFD) of the night time performance of a recently proposed conceptual system that integrates thermal storage (via phase change materials) and thermophotovoltaics for power generation. These storage integrated solar thermophotovoltaic (SISTPV) systems are attractive owing to their simple design (no moving parts) and modularity compared to conventional Concentrated Solar Power (CSP) technologies. Importantly, the ability of high temperature operation of these systems allows the use of silicon (melting point of 1680 K) as the phase change material (PCM). Silicon's very high latent heat of fusion of 1800 kJ/kg and low cost ($1.70/kg), makes it an ideal heat storage medium enabling for an extremely high storage energy density and low weight modular systems. In this paper, the night time operation of the SISTPV system optimised for steady state is analysed. The results indicate that for any given PCM length, a combination of small taper ratio and large inlet hole-to-absorber area ratio are essential to increase the operation time and the average power produced during the night time. Additionally, the overall results show that there is a trade-off between running time and the average power produced during the night time. Average night time power densities as high as 30 W/cm 2 are possible if the system is designed with a small PCM length (10 cm) to operate just a few hours after sun-set, but running times longer than 72 h (3 days) are possible for larger lengths (50 cm) at the expense of a lower average power density of about 14 W/cm 2 . In both cases the steady state system efficiency has been predicted to be about 30%. This makes SISTPV systems to be a versatile solution that can be adapted for operation in a broad range of locations with different climate conditions, even being used off-grid and in space applications.

Thermophotovoltaic energy in space applications: Review and future potential

“…Solar TPV (STPV) [41][42][43][44][45] has possible applications in near-sun space missions (Earth orbit or closer). The key advantage of STPV is the possibility of integrating extremely energetically dense thermal energy storage [46][47][48][49], theoretically enabling the development of a compact solar powered device that produces a constant power supply. Despite of its high theoretical potential, it is still premature making any confident estimation of the expected specific power of the storageintegrated STPV system, or whether it may outperform the current solution based on a combination of solar panels and electrochemical batteries.…”

Ultra high temperature latent heat energy storage and thermophotovoltaic energy conversion

“…To solve the problem we follow the quasi-stationary approach used in [15] assuming an adiabatic (loss-less) container and neglecting natural convection in the liquid. Natural convection in the liquid can be disregarded, as we will see later, due to the very low temperature gradient in the liquid silicon, which leads to a very small variation of the silicon density.…”

Design and Optimization of Thermophotovoltaic System Cavity with Mirrors

“…In addition to the material research, an efficient TPV device requires also cleverly designed cavity structures [4]. While the majority of the previous studies focused on the PV cells [8], emitters [9,10], filters [11], and other components [12][13][14][15][16], we have not found studies on the cavity configuration, which is just as important an aspect of the system as the others [17,18]. In the TPV system, components are placed in and around the cavity, whose configuration should be designed appropriately for optimized performance of the system.…”