Thermal energy storage using chloride salts and their eutectics

Abstract

Achieving the goals of the U.S. Department of Energy (DOE) Sunshot initiative requires 1) higher operating temperatures for concentrating solar power (CSP) plants to increase theoretical efficiency, and 2) effective thermal energy storage (TES) strategies to ensure dispatchability. Current inorganic salt-based TES systems in large-scale CSP plants generally employ molten nitrate salts for energy storage, but nitrate salts are limited in application to lower temperatures-generally, below 600°C. These materials are sufficient for parabolic trough power plants, but they are inadequate for use at higher temperatures. At the higher operating temperatures achievable in solar power tower-type CSP plants, chloride salts are promising candidates for application as TES materials, owing to their thermal stability and generally lower cost compared to nitrate salts. In light of this, a recent study was conducted, which included a preliminary survey of chloride salts and binary eutectic systems that show promise as high temperature TES media. This study provided some basic information about the salts, including phase equilibria data and estimates of latent heat of fusion for

Re‐establishing the paradigm for evaluating halide salt compatibility to study commercial chloride salts at 600°C–800°C

“…In the future, renewable energy must compete in the marketplace in the United States without incentives. The main advantage of concentrating solar power (CSP) is that thermal storage enables power generation to match demand better than photovoltaics or wind . The first generation of CSP did not use thermal storage and the second generation power tower CSP was deployed with nitrate salt thermal storage .…”

“…To be competitive in future markets perhaps with utility‐scale battery storage options, the third generation of CSP is envisioned to have a >50% thermal efficiency by using a supercritical CO 2 power block operating at >700°C . While a variety of thermal storage concepts can be considered, one strategy is to select a salt with higher temperature capabilities, such as chloride or fluoride salts, with chloride salts being favored due to lower costs . However, numerous recent isothermal assessments have indicated that chloride salts can be extremely corrosive to structural alloys at ≥600°C .…”

Solar salt doped by MWCNTs as a promising high thermal conductivity material for CSP

“…60%NaNO 3 , 40%KNO 3 (solar salt) and 53%KNO 3 , 40%NaNO 2 , 7%NaNO 3 (Hitec) have become the two most commonly used molten salt media in CSP (Concentrating Solar Power) plants. 1,2 Compared with carbonate, 3,4 chloride salt, 5,6 uoride salt, 7,8 sulfate 9 or molten hydroxide, 10 nitrate 11-14 is the best heat storage and heat transfer medium with low viscosity, low saturated vapor pressure, low corrosivity, large specic heat and so on. However, the thermal conductivity of solar salt is only about 0.5 W (m K) À1 , 15 which may result in lower energy conversion efficiency and limit the utilization efficiency of solar energy.…”

Investigation on performance of multi-salt composite sorbents for multilevel sorption thermal energy storage

“…It is extensively acknowledged that thermal energy storage (TES) has played the leading role in efficient utilization of renewable energy such as solar energy, geothermal and industrial waste heat [2]. TES technology is able to overcome the disadvantages of time discrepancy, distance discrepancy and instability of renewable energy by adjusting mismatch between energy supply and demand [3]. Generally speaking, TES can be divided into three aspects, i.e.…”