Thermocline Energy Storage in the Solar One Power Plant: An Experimentally Validated Thermomechanical Investigation

Abstract

The growing interest in large-scale solar power production has led to a renewed exploration of thermal storage technologies. In a thermocline storage system, heat transfer fluid (HTF) from the collection field is simultaneously stored at both excited and dead thermal states inside a single tank. A granulated porous medium included in the tank provides thermal mass for storage and reduces the amount of HTF volume required. While the thermocline offers a low-cost storage option, thermal ratcheting of the tank wall (generated by filler material reorientation from continuous thermal cycling) poses a significant design concern. A comprehensive simulation of the 170 MWht thermocline tank used in conjunction with the Solar One pilot plant is performed with a multi-dimensional two-temperature computational fluid dynamics model. In operation from 1982 to 1986, this tank was subject to extensive instrumentation, including multiple strain gages along the tank wall to monitor hoop stress. Temperature profiles along the wall material are extracted from the simulation results to compute hoop stress via finite element models and compared with the original gage data. While the strain gages experienced large uncertainty, the stresses computed from the simulation agree reasonably well with the experimental measurements. The maximum predicted hoop stress agrees to within 6.8% of the maximum stress recorded by the most reliable strain gages.