Contents lists available at ScienceDirect Solar Energy journal homepage: www.elsevier.com/locate/solener A review on sensible heat based packed bed solar thermal energy storage system for low temperature applications Abhishek Gautam ⁎ , R.P. Saini Department of Hydro and Renewable Energy, Indian Institute of Technology Roorkee, 247667, India ARTICLE INFO Keywords: Packed bed Storage element Stratification Thermal Performance Pressure drop ABSTRACT Solar thermal energy is one of the categories of renewable energy source and it is quantitative abundant and qualitative superior. It is capable to fulfil the global thermal energy demand and it emerges as a competitive option with the conventional equipment’s if these systems are incorporated with storage units. The solar thermal storage unit can also improve the equipment performance in terms of a smooth supply of energy with fluctuated solar energy collection as solar radiation varies throughout a day. Packed bed storage system is one of the feasible techniques to store the solar thermal energy which can be assembled with various solar thermal ap- plications of low temperature as well as high temperature. The present review covers the sensible heat based packed bed solar thermal energy storage systems for low temperature applications. It includes a brief discussion about packed bed, its thermodynamic background, temperature distribution within packed bed, various design parameters affecting its performance and its analysis based on the energy as well as exergy efficiency. Various experimental and numerical investigations for performance analysis of PBSS have also been reported. The economic feasibility of the PBSS and comparison of sensible heat based PBSS with latent heat based PBSS has also been discussed in detail. 1. Introduction Energy is an essential segment for the advancement of industry, public service and transport (Gautam et al., 2018). It is the prime mover for the monetary benefit and advancement of every nation. Its demand is consistently expanding because of the worldwide population growth and rising living standards. As per a report of world energy outlook 2017, although the current rate of escalation in energy demand is quite low as compared to the past few years, it is still expected to expand by 30% between 2017 and 2040 which is nearly equivalent to adding a new China and India in current demand (Energy Information Administration, 2011). In such scenario, renewable energy resources are the assets, specially solar energy and its modernization have chances to provide solutions of constantly increasing energy related being faced by various countries (Rawea and Urooj, 2018). From the last few decades, solar energy is emerging as a feasible alternative, especially for the thermal applications. However, due to intermittent nature of solar energy, the solar thermal systems require a storage unit for their efficient utilization. Reduced energy cost, redis- tributed energy, reduced initial and maintenance cost, diminished size and most efficient usage of the equipment’s are the characteristics ex- pected from the storage unit in order to make it a competitive approach to its conventional counterparts (Lefebvre and Tezel, 2017). The solar thermal energy can be store in the form of sensible heat, latent heat and thermo-chemical energy. The scope of this review is limited to sensible heat based TES systems for low temperature applications. Greenhouse heating, solar drying, solar air heaters and space heating are some applications falls under this category whose working temperature range is up to 100 °C. Storage tank (Brosseau et al., 2004), fluidized bed system (Almen- dros-Ibáñez et al., 2018), packed bed storage system (PBSS) and con- crete blocks (Girardi et al., 2017) are the sensible heat storage methods generally integrated with low temperature solar thermal applications. PBSS is the suitable method for TES due to its simple mechanism and economic feasibility (Kuravi et al., 2013). The required characteristics of an efficient PBSS for low temperature applications are given in Fig. 1. A typical PBSS incorporate an insulated tank, storage material, a screen whose role is to support the bed of packing elements, some supporting arrangement for the screen, inlet and outlet ducts as shown in Fig. 2 (Duffie and William, 2013). The insulated tank contains sto- rage elements in the form of fixed bed and utilized as the primary heat storage medium in which the thermal energy can be stored by raising the temperature of the material. Thermal stratification is desirable in an efficient PBSS, therefore the use of packing elements with having high https://doi.org/10.1016/j.solener.2020.07.027 Received 20 November 2018; Received in revised form 6 July 2020; Accepted 9 July 2020 ⁎ Corresponding author. E-mail address: gautam0120abhishek@gmail.com (A. Gautam). Solar Energy 207 (2020) 937–956 0038-092X/ © 2020 International Solar Energy Society. Published by Elsevier Ltd. All rights reserved. T