Techno-Economic Analysis of Using Reversible Turbomachinery for Pumped Thermal Energy Storage Systems

The objective of this paper is to assess the techno-economic performance of different cycle configurations for pumped thermal energy storage (PTES), including the effects of charging electricity cost. Reversible turbomachinery was employed to reduce the capital cost of the system. Brayton cycles with different working fluids and a subcritical Rankine cycle operating with ammonia were compared. Both liquid and packed bed thermal storage were investigated. A new cost correlation for turbomachines, initially established for the turbines of organic Rankine cycles, was developed for compressors and reversible machines. This correlation is based on the number of stages and physical size of the machine, which were estimated considering thermodynamic as well as mechanical limitations. The results indicate that for a plant size of 50 MW and a discharge duration of 8 hours, the Brayton system with liquid storage and helium as a working fluid has the lowest levelized cost of storage at 0.138/$kWh, mainly due to the high thermal conductivity of the fluid. Packed bed thermal energy storage systems were found to be more expensive than liquid storage systems due to the large cost of the pressure vessels, with cost parity reached at a discharge duration of 4 hours. However, at this duration lithium-ion batteries are likely to be cheaper. The results suggest that the levelized cost of storage for the Rankine cycle based system is slightly higher at 0.151/$kWh.