Using Sand and other Small Grained Materials as Heat Storage Medium in a Packed Bed HTTESS

Packed bed heat storage systems offer a great potential for the further reduction of the LCOE of CSP-plants. The use of cost effective and local available storage materials like gravel or silica sand is a key factor for such systems. But also concerning the performance during charging and discharging of the system, the storage material has a huge influence. In this paper the influence of small grained storage material is investigated using theoretical models and experimental results. The results show, that with small grained materials with diameters of 2 mm or less a very sharp temperature behavior could be achieved during charging. The boundary layer between the hot and the cold storage material (the so called thermocline) is very sharp for all considered air flow rates. The paper concludes with a simplified model of the thermocline for the design of the storage system and the selection of the most critical parameters. (C) 2015 The Authors. Published by Elsevier Ltd.