High-temperature thermal energy storage (TES) has been widely used in concentrated solar thermal power generation systems and today it is considered one of the most promising technologies for grid-scale electricity storage. In a conventional TES system, the charging and discharging processes are carried out in an indirect contact heat exchanger, which involves transportation losses. Therefore, a high temperature TES that is charged with high-voltage electrical power and discharged with the working fluid of the power cycle is proposed in the present study. A modular design has been developed, which can be extended to any scale. This involves a set of elements made up of an electric heater surrounded by a matrix of ceramic material, which works as storage medium, and air as working fluid for the discharge. The geometry is optimized to have high energy storage density, high air outlet temperature, and minimum pressure drop. Different cross sections, sizes, and void fractions are investigated. The results showed that the elliptical cross section provides the best performance in terms of pressure drops. Moreover, with the elliptical cross section the heat exchange between air and solid material is 2 times more efficient compared to circular and hexagonal elements. Using smaller electric heaters, but larger in number, improves the air heating rate through the reservoir. Increasing the air velocity by 10 times (from 0.1 to 1 m s-1), the heat exchange decreases by 60 to 70% for all the considered cases. Doubling the void fraction from 0.3 to 0.6 causes a reduction in the air heating rate of 35-50%. According to the boundary conditions, the optimal layout of the TES is 10m × 9.6m × 20m. With an air velocity of 0.3 m s-1 and a void fraction of 40%, pressure drop with elliptical elements is 1.8 Pa · m-1. Using magnesium oxide as thermal storage medium, the energy density of the proposed thermal storage design results in 390 kWhth m-3
DESIGN AND OPTIMIZATION OF A HIGH TEMPERATURE THERMAL ENERGY STORAGE WITH DIRECT ELECTRIC CHARGING AND CONVECTIVE DISCHARGING
Pecchini M.;Stoppato A.
;Benato A.
2024
Abstract
High-temperature thermal energy storage (TES) has been widely used in concentrated solar thermal power generation systems and today it is considered one of the most promising technologies for grid-scale electricity storage. In a conventional TES system, the charging and discharging processes are carried out in an indirect contact heat exchanger, which involves transportation losses. Therefore, a high temperature TES that is charged with high-voltage electrical power and discharged with the working fluid of the power cycle is proposed in the present study. A modular design has been developed, which can be extended to any scale. This involves a set of elements made up of an electric heater surrounded by a matrix of ceramic material, which works as storage medium, and air as working fluid for the discharge. The geometry is optimized to have high energy storage density, high air outlet temperature, and minimum pressure drop. Different cross sections, sizes, and void fractions are investigated. The results showed that the elliptical cross section provides the best performance in terms of pressure drops. Moreover, with the elliptical cross section the heat exchange between air and solid material is 2 times more efficient compared to circular and hexagonal elements. Using smaller electric heaters, but larger in number, improves the air heating rate through the reservoir. Increasing the air velocity by 10 times (from 0.1 to 1 m s-1), the heat exchange decreases by 60 to 70% for all the considered cases. Doubling the void fraction from 0.3 to 0.6 causes a reduction in the air heating rate of 35-50%. According to the boundary conditions, the optimal layout of the TES is 10m × 9.6m × 20m. With an air velocity of 0.3 m s-1 and a void fraction of 40%, pressure drop with elliptical elements is 1.8 Pa · m-1. Using magnesium oxide as thermal storage medium, the energy density of the proposed thermal storage design results in 390 kWhth m-3
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