Thermal analysis of solar thermal energy storage in a molten-salt thermocline

Abstract

A comprehensive, two-temperature model is developed to investigate energy storage in a molten-salt thermocline. The commercially available molten salt HITEC is considered for illustration with quartzite rocks as the filler. Heat transfer between the molten salt and quartzite rock is represented by an interstitial heat transfer coefficient. Volume-averaged mass and momentum equations are employed, with the Brinkman-Forchheimer extension to the Darcy law used to model the porous-medium resistance. The governing equations are solved using a finite-volume approach. The model is first validated against experiments from the literature and then used to systematically study the discharge behavior of thermocline thermal storage system. Thermal characteristics including temperature profiles and discharge efficiency are explored. Guidelines are developed for designing solar thermocline systems. The discharge efficiency is found to be improved at small Reynolds numbers and larger tank heights. The filler particle size strongly influences the interstitial heat transfer rate, and thus the discharge efficiency.

Off-design performance of concentrated solar heat and coal double-source boiler power generation with thermocline energy storage

“…Unlike the conclusions from Yang and Garimella [36],of which the thickness increased with Re number and velocity, Fig. 7 shows that the discharging efficiency or the thermocline thickness can be decreasedwith a larger tank diameter and a smaller velocity.…”

“…By selecting the center point in the discharging process to compare like Yang and Garimella [36], the results are shown in Fig. 8(a), where the thickness for Re=10 is indeed wider than that that of Re=1, similar to Ref.…”

“…In terms of thermocline storage, the design method can be found in [36] whilethe previous research [30] showed that on account of the operation characteristics of thermocline tank, 40%overdesign of the tank volume is necessary.Apart from that, to bear the gravity of the fillers the height of the tank should not exceed 11.89m. In another system-level research about the SPT plant with molten salt [31], the minimum of 2h storage was suggested for the stable performance in the daytime.…”

Latent heat augmentation of thermocline energy storage for concentrating solar power – A system-level assessment

“…To facilitate direct comparison with thermocline tanks that use conventional sensible-heat filler materials, a hypothetical PCM filler is considered with density, specific heat, and thermal conductivity equivalent to those of quartzite rock: 2500 kg/m 3 , 830 J/kg-K, and 5 W/m-K, respectively [15,16]. In reality, phase-change materials suitable for latent heat storage tend to have lower thermal conductivities as well as densities that vary with temperature.…”

Design of a 25 MWe Solar Thermal Power Plant in Iran with Using Parabolic Trough Collectors and a Two-Tank Molten Salt Storage System

“…A thermal storage system provides extra thermal power for a solar power plant to produce electricity without the use of fossil fuel at noninsolation times, particularly in a peak point of demand [13]. The most progressive thermal storage system to store extra thermal power is the two-tank storage system where the same oil which circles in collectors is used in the storage system though the oil price is quite costly and its usage will substantially increase the expense of the storage system [14].…”