Abstract:

The gravity energy storage system (GESS) has attracted extensive attention owing to its long-term operation, large capacity, zero self-discharge rate, and high safety. The energy efficiency level is a critical factor affecting the large-scale application of GESS. Firstly, for the vertical GESS based on belt drive, the sliding friction of the moving/fixed pulley relative to the bearing surface in the mechanical link, the ball bearing friction in the traction system, the elastic sliding friction of the drive belt relative to the pulley, and the copper loss, iron loss, wind friction, and stray loss of the motor in the electrical link are analyzed, and the theoretical calculation method for the efficiency and loss of each link of the system is derived. Secondly, a numerical example is provided for the proposed calculation method. The results show that the efficiency of the mechanical link decreases slightly as the mass block increases; the charging efficiency of the system initially increases and then decreases with increasing mass block; the discharging efficiency increases with the mass block; and under discharging conditions, the proportion of mechanical loss in the system is significantly higher than under charging conditions. Finally, a 1.1 kW prototype is built to verify the calculation results. The experimental results show that when the mass block is 127.35 kg, the measured motor loss proportions in charging and discharging states are 82.77% and 72.42%, respectively, which are close to the theoretical values of 80.56% and 72.96% obtained from the numerical example. The theoretical variation curve of the system's charging and discharging efficiencies with respect to the mass block exhibits the same trend as the measured curve, which verifies the correctness and practicability of the proposed energy efficiency analysis method.

Key words: vertical gravity energy storage, belt drive, efficiency analysis, loss calculation