Energy, exergy, and economic analyses of a new liquid air energy storage system coupled with solar heat and organic Rankine cycle

Abstract

Liquid air energy storage (LAES) has attracted more and more attention for its high energy storage density and low impact on the environment. However, during the energy release process of the traditional liquid air energy storage (T-LAES) system, due to the limitation of the energy grade, the air compression heat cannot be fully utilized, resulting in a low round trip efficiency (RTE). In addition, coupling solar heat can improve the energy grade of the air during the discharging cycle, which shows a promising prospect. Therefore, a new LAES system coupled with solar heat and organic Rankine cycle (LAES-S-O) is proposed in this paper. Compared with T-LAES system, the thermal oil absorbs solar heat to reheat the air, which improves the output power of the air turbine. Meanwhile, two parts of excess heat of the system are respectively used as heat source to drive organic Rankine cycle (ORC), which greatly improves the RTE of the system. Since the influences of the split fraction (α) of the air compression heat on the system performance are not deeply studied in the previous researches, the factors affecting both the maximum αmax and the minimum αmin are analyzed first. Then the effects of ambient temperature, solar irradiation intensity, energy storage pressure, inlet air temperature of the throttle valve, mass flow rate of the sol-oil and service life on the new system performance are studied with the change of the split fraction. Meanwhile, the energy, exergy and economic performance analyses of the new system are carried out. The results show that the RTE of the new LAES-S-O system is 73.33%, 44.98% higher than that of the T-LAES system. Exergy efficiency of energy storage process and energy release process are 82.71% and 79.18% respectively. The payback period is 9.582 years, the levelized cost of electricity (LCOE) in the lifetime is 0.1434 $/kWh, and the net present value (NPV) is 159.537 million $ over a 30-year period.