Steady state analysis of a storage integrated solar thermophotovoltaic (SISTPV) system

Abstract

This paper presents the theoretical analysis of a storage integrated solar thermophotovoltaic (SISTPV) system operating in steady state. These systems combine thermophotovoltaic (TPV) technology and high temperature thermal storage phase-change materials (PCM) in the same unit, providing a great potential in terms of efficiency, cost reduction and storage energy density. The main attraction in the proposed system is its simplicity and modularity compared to conventional Concentrated Solar Power (CSP) technologies. This is mainly due to the absence of moving parts. In this paper we analyze the use of Silicon as the phase change material (PCM). Silicon is an excellent candidate because of its high melting point (1680 K) and its very high latent heat of fusion of 1800 kJ/kg, which is about ten times greater than the conventional PCMs like molten salts. For a simple system configuration, we have demonstrated that overall conversion efficiencies up to ~35% are approachable. Although higher efficiencies are expected by incorporating more advanced devices like multijunction TPV cells, narrow band selective emitters or adopting near-field TPV configurations as well as by enhancing the convective/conductive heat transfer within the PCM. In this paper, we also discuss about the optimum system configurations and provide the general guidelines for designing these systems. Preliminary estimates of night time operations indicate it is possible to achieve over 10 h of operation with a relatively small quantity of Silicon.

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

“…The key aspect of the design is the option of integrating a phase-change material (PCM), in which a solid is melted, capturing and storing a considerable amount of thermal energy as latent heat. In this arrangement, the PV cells can have a back side reflector (BSR) that reflects back to the emitter the non-absorbed radiation (mainly the subbandgap photons) enabling an extremely high PV conversion efficiency (much higher than conventional solar PV cells Algora, 2010, 2012;Datas et al, 2013;Gartling, 1978;Gau and Viskanta, 1984). As explained elsewhere (Bauer, 2011;Chubb, 2007), TPV technology has a great potential to boost the heat-to-electricity conversion efficiency, even above 50%.…”

“…More recent works Datas et al, 2013;Gilpin et al, 2011;Scharfe et al, 2011) per unit area and storage ability. One of the main characteristics of these kinds of SISTPV systems is the use of very high melting point phase change materials (PCM).…”

“…However, its application in terrestrial applications is unlikely owing to cost and compatibility issues. For terrestrial applications, however, silicon has been identified as the ideal candidate Datas et al, 2013;Gilpin et al, 2011;Scharfe et al, 2011). This is mainly because of its very high heat of fusion (1800kJ/kg) and low price (about $1.70/kg which translates to $0.95MJ/kg .…”

“…In our previous work (Datas et al, 2013), we presented a full optimisation of a silicon-based SISTPV system in the steady state. The key characteristic of this system is the tapered configuration for the PCM tank which allows the proper melting of the full PCM and enhancement of the conversion efficiency simultaneously.…”

“…However, in order to evaluate the SISTPV system for a full day/ night cycle, it is critical to calculate the performance for night time operation. Therefore, it is the objective of this paper to analyse the night time operation of SISTPV systems optimised in Datas et al (2013) for the steady state. We assume a quasi-stationary approach to model the transient response of the system after sunset.…”