General volume sizing strategy for thermal storage system using phase change material for concentrated solar thermal power plant

Abstract

h i g h l i g h t sWe present a method of sizing a thermocline thermal storage system for a CSP plant. Phase change materials (PCM) are considered for this study. Sizing criterion is that the discharged fluid temperature is above a cutoff point. The sizing procedures were presented through one design example. Latent heat storage system (LHSS) Phase change material (PCM) General volume sizing strategy Enthalpy-based 1D transient model a b s t r a c tWith an auxiliary large capacity thermal storage using phase change material (PCM), Concentrated Solar Power (CSP) is a promising technology for high efficiency solar energy utilization. In a thermal storage system, a dual-media thermal storage tank is typically adopted in industry for the purpose of reducing the use of the heat transfer fluid (HTF) which is usually expensive. While the sensible heat storage system (SHSS) has been well studied, a dual-media latent heat storage system (LHSS) still needs more attention and study. The volume sizing of the thermal storage tank, considering daily cyclic operations, is of particular significance. In this paper, a general volume sizing strategy for LHSS is proposed, based on an enthalpy-based 1D transient model. One example was presented to demonstrate how to apply this strategy to obtain an actual storage tank volume. With this volume, a LHSS can supply heat to a thermal power plant with the HTF at temperatures above a cutoff point during a desired 6 h of operation. This general volume sizing strategy is believed to be of particular interest for the solar thermal power industry.

Application of phase change materials for thermal energy storage in concentrated solar thermal power plants: A review to recent developments

“…They also concluded that a PCM method is particularly useful if the heat is needed at a temperature near the melting temperature. Xu et al [134] found similar phenomenon when they calculated and compared the thermal storage efficiency for a packed-bed TES system using different storage media.…”

“…Xu et al [134] performed a simple cost analysis for the comparison between SHTES and LHTES, based on a previously developed 1D enthalpy-based transient model [139]. According to the general volume sizing strategy proposed by the authors [134,197], the storage media cost for four different systems (SHTES with granite rocks under 6 h charge, LHTES with KOH under 8 h charge, LHTES with KOH under 6 h charge, LHTES with 58% NaCl-42% KCl under 6 h charge) were calculated and compared, for a parabolic trough CSP plant with 60 MW electrical power output at a thermal efficiency of 35%.…”

“…Using the prices from several different distributors mentioned by Strasser and Selvam [196], the cost analysis listed in Ref. [134] has been revised by replacing Therminol VP-1 with Solar Salts, and the updated capacity cost for each system is shown in Table 13. The results show that LHTES using salt (58% NaCl-42% KCl) with 6 h charge has the lowest capacity cost of $20.5/kW h, which is about 43% less than that of SHTES using granite rock with 6 h charge.…”

“…In order to explorer the relationship between the melting temperature of PCM and the cutoff temperature, the current authors performed numerical investigation, using a 1D enthalpy-based transient model [139] and the general volume sizing strategy [134]. In this analysis, two different PCMs were adopted (PCM-1: KOH; PCM-2: NaCl-KCl, 58-42 wt.%), and the cutoff temperature was chosen as 360°C, which was the same as the melting temperature of PCM-2.…”

“…According to the general volume sizing strategy proposed by the authors [134,197], the storage media cost for four different systems (SHTES with granite rocks under 6 h charge, LHTES with KOH under 8 h charge, LHTES with KOH under 6 h charge, LHTES with 58% NaCl-42% KCl under 6 h charge) were calculated and compared, for a parabolic trough CSP plant with 60 MW electrical power output at a thermal efficiency of 35%. The authors [134] reported the capacity cost of three different LHTES systems, which are much higher than the capacity costs listed in Ref. [196], and this is because the cost of Therminol VP-1 HTF is much higher than that of 'Solar Salts' HTF, for example the cost of Therminol VP-1 is $26.3/kg, while the cost of Solar Salt is only $0.5/kg.…”