Abstract
High-temperature latent heat storage (LHS) systems using a high-temperature phase change medium (PCM) could be a potential solution for providing dispatchable energy from concentrated solar power (CSP) systems and for storing surplus energy from photovoltaic and wind power. In addition, ultra-high-temperature (>900 °C) latent heat storage (LHS) can provide significant energy storage density and can convert thermal energy to both heat and electric power efficiently. In this context, a 2D heat transfer analysis is performed to capture the thermo-fluidic behavior during melting and solidification of ultra-high-temperature silicon in rectangular domains for different aspect ratios (AR) and heat flux. Fixed domain effective heat capacity formulation has been deployed to numerically model the phase change process using the finite element method (FEM)-based COMSOL Multiphysics. The influence of orientation of geometry and heat flux magnitude on charging and discharge performance has been evaluated. The charging efficiency of the silicon domain is found to decrease with the increase in heat flux. The charging performance of the silicon domain is compared with high-temperature LHS domain containing state of the art salt-based PCM (NaNO3) for aspect ratio (AR) = 1. The charging rate of the NaNO3 domain is observed to be significantly higher compared to the silicon domain of AR = 1, despite having lower thermal diffusivity. However, energy storage density (J/kg) and energy storage rate (J/kgs) for the silicon domain are 1.83 and 2 times more than they are for the NaNO3 domain, respectively, after 3.5 h. An unconventional counterclockwise circular flow is observed in molten silicon, whereas a clockwise circular flow is observed in molten NaNO3 during charging. The present study establishes silicon as a potential PCM for designing an ultra-high-temperature LHS system.
Highlights
Increased global energy consumption, limited reserve of fossil fuels, and their harmful impact on the environment have compelled a paradigm shift towards sustainable energy sources [1]
The present study evaluated the charging and discharge performance of a hightemperature silicon-based latent heat storage (LHS) system using the effective heat capacity technique
The charging performance of high-temperature LHS with silicon was compared with the NaNO3 domain
Summary
Increased global energy consumption, limited reserve of fossil fuels, and their harmful impact on the environment have compelled a paradigm shift towards sustainable energy sources [1]. Especially solar and wind energy can act as potential alternatives to address the challenges faced due to conventional fuels. Solar energy is considered the most attractive sustainable renewable resource due to its relatively low cost and abundance. Thermal energy storage (TES) can address the discontinuity of solar energy by storing heat during the duration of sunshine hours and releasing it during periods with no sun [4,5]. TES enables an increase in overall efficiency and better reliability in an energy system which can lead to better economics, reductions in investment and running costs, and a lower rate of pollution of the environment [6]. TES is becoming an integral component of third generation CSP which can simultaneously improve the dispatchability of solar energy, reliability and effectiveness of CSP systems
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