The conventional photothermal-assisted scheme adopted by advanced adiabatic compressed air energy storage (AA-CAES) has equal stages of expanders and high-temperature reheaters, and is equipped with a regenerator to waste heat recovery, which is relatively complex and requires high solar heat supply and solar irradiance. In this paper, a novel photothermal-assisted AA-CAES (PT-AA-CAES) with a simpler structure and suitable for low sol. The conventional photothermal-assisted scheme adopted by advanced adiabatic compressed air energy storage (AA-CAES) has equal stages of expanders and high-temperature reheaters, and is equipped with a regenerator to waste heat recovery, which is relatively complex and requires high solar heat supply and solar irradiance. In this paper, a novel photothermal-assisted AA-CAES (PT-AA-CAES) with a simpler structure and suitable for low solar irradiance is designed, which adopts 3-stage expansion and 2-stage high-temperature reheat. The thermodynamic model of PT-AA-CAES system is established, and a comprehensive evaluation coefficient combining exergy efficiency and energy storage density is proposed. The numerical results demonstrate that the compressor unit outlet pressure and expansion unit inlet pressure with the optimal comprehensive performance are 10 MPa and 4 MPa. Furthermore, when the solar irradiance is below 690 W/m2, 660 W/m2, and 600 W/m2, the output work, exergy efficiency, and energy storage density of the novel PT-AA-CAES system will surpass those of the conventional PT-AA-CAES system with the same solar heat consumption, and at a solar irradiance of 580 W/m2, the exceeded values are 44.3 kW h, 2.03%, and 0.15 kW h/m3, respectively. These conclusions can assist the AA-CAES system in the selection of unit pressures and photothermal-assisted scheme.••Advanced adiabatic compressed air energy storagePhotothermal-assisted schemeThermodynamic analysisComprehensive evaluation coefficientA solar collector area, m2C heat capacity, kJ/(K·h)cp specific heat at constant pressure, kJ/(kg·K)cv specific heat at constant pressure, kJ/(kg·K)h enthalpy of gas per unit mass, kJ/kgH With the growing shortage of fossil fuels and increasingly serious environmental concerns, the world's energy sources are moving in the direction of renewable, green, and efficient [1,2]. In this context, renewable energy is developing rapidly and will occupy a dominant position in the future energy structure [3,4]. For instance, Germany aims to increase the share of renewable energy to more than 55% in 2035. However, since renewable energy generation is intermittent and unstable, its widespread development and popularization would unavoidably threaten the stability and security of the power grid [6,7]. To ensure the safe and stable operation of the grid, energy storage technology stands out. Because this technology can perform peak shaving and valley filling in the power grid, and absorb the impact on the grid when renewable energy generation is connected to the grid [8,9]. Among many energy storage technologies, pumped storage is the most mature large-scale energy storage technology, and compressed air energy storage (CAES) technology is a storage technology that can match the scale of pumped storage. It has several benefits, including a strong economy, low operating cost, and a fast constructing time, and it is now the most promising large-scale energy storage technology [10,11].To address the issues of low efficiency and the need for re-fueling in traditional CAES systems, the advanced adiabatic CAES (AA-CAES) system employs int. 2.1. AA-CAESThe schematic diagram of the AA-CAES system is shown in Fig. 1. During the energy storage process, the air enters the compressor unit (CU) for multi-stage compression (1–2, 3–4) and inter-stage cooling (2–3, 4–5) driven by the electric motor, and the cooled high-pressure air then is stored in the GSC (4–5). Moreover, the cooling water from the cold tank cools the compressor outlet high-pressure air in the intercooler at each stage (13–15, 14–16), then goes into the hot tank to store the compressed heat (15–17, 16–17). During energy release, the high-pressure air inside the GSC is throttled to a stable pressure after passing through the throttle valve (6–7), then absorbs the heat from the hot water coming out of the hot tank in the reheater at all levels (7–8, 9–10), and then flows into the expander at all levels to do work (8–9, 10–11).2.2. Photothermal-assisted scheme designThe schematic diagrams of the PT-AA-CAES systems with the two PTSs are shown in Fig. 2 (a) and (b). The PTS1, the novel PTS proposed in this paper, uses the scheme of 3-stage expansion and 2-stage high-temperature reheat. During energy release, hot water in the hot tank preheats the throttle valve out.
