Thermal evaluation of molten salts for solar thermal energy storage

Abstract

Molten salts are known for having good heat transfer properties to be used in thermal storage. This application has become important in the development of thermal technologies for solar energy concentration. The operating principle of these technologies is based on the concentration of sun rays by mirrors to achieve high temperatures and aims to operate turbines coupled with electric generators to produce electricity. Therefore, alkali nitrates and sodium nitrite are good candidates due to the low melting point and excellent heat capacity. These properties produce a broad molten salt operating range and enable effective thermal storage in solar power plants. But one of the critical parameters is the degradation because the cyclic process of heating / cooling. It is important to study the thermal properties in order to determine the operating conditions and lifetime during processing.The purpose of this study is to evaluate the melting point and thermal stability of conventional salt systems, such as the Solar Salt (60% NaNO 3 -40% -KNO 3 , Tm = 220 °C) and HITEC (7% NaNO 3 -53% KNO 3 -40%NaNO 2 , Tm = 142 °C), and a novel eutectic mixture. The physical and chemical properties of the studied salts were evaluated by Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA) and morphology was observed in SEM images. In order to compare experimental results with theoretical calculations, the eutectic temperature and heat capacity were calculated with Factsage® thermodynamic software.Melting point was found to be lower than that of conventional salts due to the Lithium Nitrate addition in the systems.

Encapsulated Nitrates Phase Change Material Selection for Use as Thermal Storage and Heat Transfer Materials at High Temperature in Concentrated Solar Power Plants

“…In the presented paper, LiNO 3 /NaNO 3 /KNO 3 is used to represent this eutectic mixture composed of 30 wt % of LiNO 3 , 20 wt % of NaNO 3 and 50 wt % of KNO 3 . [81] 2320 [82] In addition to these PCMs, some nitrate-free composites were also included in the simulation since it was also of interest to confirm that the nitrates have better performance as PCMs than other composites, such as MgCl 2 and the salt of the eutectic mixture of MgCl 2 and NaCl composed of 57 and 43 mol %, respectively, which is represented as MgCl 2 /NaCl. Table 3 collects information concerning the characterization of readily-made capsules for PCMs and shell selections.…”

Improving the Performance of Solar Heat Collector Using Molten Salts

“…melting point, heat capacity and thermal stability. Melting point and heat capacity and thermal stability are the most important characteristics to be taken into consideration when designing any salt storage system [10,11]. Thermal properties for PCM materials include (Suitable phase-transition temperature, good heat transfer and high latent heat of transition), and physical properties include (high density, small volume change and low vapor pressure) and the chemical properties (no toxicity, long term chemical stability, and nonexplosive) [12].…”

Effect of sand and moisture on molten salt properties for open direct absorption solar receiver/storage system

“…One way to use this solar energy is concentrated solar power (CSP) with thermal energy storage (TES). This technology is capable of storing enough energy for continuous heat production even when there is limited sunlight or at night 2 . The state of the art production plant technology is a CSP with a two-tank molten salt system using solar salt (60 wt.…”