Dynamic modeling and simulation of a concentrating solar power plant integrated with a thermochemical energy storage system

Highlights

• Dynamic behaviors of a CSP plant coupled with a TCES unit were studied.

• Individual component models written in modelica were selected and developed.

• These models were then parametrized and interconnected to build the global model.

• Three TCES integration concepts were compared under realistic variable conditions.

• Both the continuous production mode and the peak production mode were investigated.

Abstract

This paper presents the dynamic modeling & simulation of a concentrating solar power (CSP) plant integrated with a thermochemical energy storage (TCES) system. The TCES material used is calcium hydroxide and the power cycle studied is a Rankine cycle driven by the CSP. Firstly, dynamics models of components written in Modelica language have been selected, developed, parametrized, connected and regulated to create the CSP plant with different TCES integration concepts. Then simulations were performed to determine and compare the energy efficiency, water consumption and energy production/consumption of three integrations concepts for two typical days (summer and winter) and for a basic continuous production mode. After that, a feasibility study has been performed to test a peak production scenario of the CSP plant.

The results showed that the TCES integration could increase the overall efficiency of the CSP plant by more than 10%. The Turbine integration concept has the best global efficiency (31.39% for summer; 31.96% for winter). The global electricity consumption of a CSP plant with TCES represents about 12% of its total energy production for a summer day and 3% for a winter day. An increased nominal power by a factor of 10 could be reached for the peak production mode within one hour using the Turbine integration concept, but with a lower global efficiency (17.89%).

Introduction

Concentrating solar power (CSP) is expected to play a key role in the future energy transition scenarios towards a more electrified world with low-carbon technologies [1]. Meanwhile, thermal energy storage (TES) systems become indispensable to increase the dispachability and the economic competitiveness of modern large-scale powerful CSP plants [2, 3]. Currently more than 80% of the CSP plants under construction or planned incorporate TES systems [4, 5].

Sensible storage using molten salt is the most developed and commonly used TES technology for existing CSP plants because of its simplicity, reliability and cost-effectiveness [6, 7]. However, the salt corrosiveness [8], [9], [10], the limited working temperature [11, 12] and the risk of salt solidification [13, 14] are the major drawbacks remaining to be solved. Other sensible TES systems have then been proposed and studied during the last years, as summarized in recent review papers [15, 16]. As an alternative, latent heat storage using phase change materials (PCMs) is under intensive investigation, owing to their high density and almost constant phase change temperature during charging or discharging [17, 18]. Special attention has been focused on the improvement of their limited thermal conductivity through encapsulation as well as nanomaterials additives [19, 20].

Another trend on the TES systems for CSP plants is the development of thermochemical energy storage (TCES) technology based on reversible endothermic/exothermic chemical reactions involving a large amount of reaction heat. TCES systems become a very attractive option because of their high energy density (up to 10 times greater than latent storage) and the long storage duration at ambient temperature [21]. Latest advances on the thermochemical materials, reactors and processes are reviewed and summarized in Refs [22, 23]. Recently, great efforts have also been devoted to investigate the appropriate coupling of the TCES system with the power generating cycle (e.g., Rankine cycle; Brayton cycle, etc.) of the CSP plant [e.g., [24], [25], [26], [27], [28], [29], [30]]. This process integration issue plays actually a key role on the adaptation of the TCES technology to the future CSP plants. Particularly in our previous study [30], three TCES integration concepts using Ca(OH)₂/CaO couple have been proposed. Energy and exergy analyses results indicated that compared to a reference plant without storage, the TCES integration could significantly improve the adaptability and dispatchability of the CSP plant with the increased power production [30].

While most of the earlier studies reported in the literature are focused on conceptual or static analysis, detailed exploration of the TCES process integration issue is still lacking. The dynamic behaviors of CSP plant with TCES integration are of particular importance because this type of installation is inherently subjected to transient boundary conditions such as the varying solar irradiation. Moreover, the dynamic simulations also make it possible to highlight the influences of thermal inertia, which has usually been neglected in the static analysis but plays an important role regarding the real operations of the CSP plant.

As the following work of our previous study [30], this paper makes a step forward by presenting the dynamic modeling & simulation of a CSP plant integrated with a TCES system under real conditions. Dynamic models of each component written in the Modelica language have been either adopted from the Dymola library or developed in-house. These models have then been parametrized and further interconnected to build the global model for the CSP plant with TCES integration. The main objectives of this study include: (1) to characterize, for the first time, the dynamic behaviors of a CSP plant coupled with a TCES unit; (2) to compare the performances of different TCES integration concepts under realistic variable environmental conditions; (3) to showcase the feasibility of the basic continuous production mode and the peak production mode by implementing advanced control strategies. The contributions of this paper are important because it will expand the limited literature and provide additional insights on the dynamic behaviors of CSP plants with TCES integration. The results obtained may be used for the large deployment of the TCES technology in CSP plants.

The rest of the paper is organized as follows. Section 2 introduces the methodology used for this study, including the proposed TCES integration concepts, the mathematic model for individual component, the operation mode, the control and the initialization parameters. Section 3 presents and compares the dynamic simulation results for the CSP with different TCES integration concepts under the continuous production mode. Section 4 reports a feasibility study on the peak production mode with the Turbine integration concept. Finally, main findings are summarized in Section 5.