Thermal Storage Filler Material Distribution for the Polyphem Project

The aim of the POLYPHEM project (H2020 program, Ref N. 764045) is to increase the flexibility and improve the performance of small solar tower power plants. The concept consists in implementing a combined cycle formed by a solarized micro gas-turbine and a Rankine organic cycle machine, with an integrated thennal storage device between the two cycles. The need for cooling is minimal. A prototype plant of 60 kW(el) with a thermal storage of 2 MWh net capacity is designed, built and installed on the site of the experimental solar tower of Themis in Targasonne (France). The objective of the project is to validate the technical choices under test conditions representative of actual operating conditions. Among the options of thermal energy storage (TES) a thermocline tank with solid filler and thermal oil as heat transfer fluid has been selected. The selected oil, Jarythenn DBT, presents very low vapor pressure (45999 Pa (abs), i.e. -0.55 barg at 340 degrees C), which allows for a storage tank at atmospheric pressure. The thermal storage concept to design is a thermocline tank with concrete for walls, foundations and filler. The filler is made of bricks, so it is expected to avoid most of the thennal ratcheting issues associated to tillers. This paper presents the different internal disposals of the bricks in the tank, and the influence these disposals may have both on the thermohydraulic behavior of the storage thermocline tank and on the stored energy.