Advanced Thermocline Concepts for Thermal Energy Storage

Kurzfassung

Molten salt thermal energy storage (TES), originating from concentrating solar power (CSP), has gained great potential for novel industrial applications. Examples are the flexibilization of chemical plants, the conversion of conventional power plants into Power-to-Heat-to-Power storage plants or the decoupling of industrial processes from supply and demand. The CSP Eranet Project Newcline aims to significantly improve TES systems. One key aspect is the utilization of structured filler refractories made of novel materials and encapsulated phase change material (PCM) to reduce storage costs and enhance discharge efficiencies. In a first step, extensive parametric studies for a 1000 MWh TES have been carried out. Outlet temperature drop as well as void fraction and hydraulic diameter of the filler refractories have been investigated (Figure 1). As a result, the exergetic efficiency of the thermocline system in comparison with a two-tank-system can be maintained up to 99%. Simultaneously, the utilized molten salt can be significantly reduced. Based on these findings, potential candidate materials have been tested for 2000 hours for compatibility with Solar Salt at temperatures of 600 °C, see Figure 2. A rectangular clinker based refractory material and a specifically designed material from DLR’s project partner Kraftblock will be further tested in large scale within DLR’s test facility TESIS. Currently, the experimental campaign for these refractory bricks is being prepared, see Figure 3 and Figure 4. After this campaign, an encapsulated phase change material will be added to the facility. This work provides the results of the material selection process from a thermodynamic, economic and chemical point of view and gives insight into the planned 4 MWh-scale test campaigns with refractory bricks and PCM.