Session: 03-03 Pumped Thermal Energy Storage

Paper Number: 106297

106297 - Thermo-Economic Assessment of Pumped Thermal Electricity Storage Systems Employing Reversible Turbomachinery 

Pumped thermal electricity storage systems (PTES) are being considered as a novel option for low-cost, location-independent, long duration (>8h) electricity storage. As the PTES technology is still in development stage, many competing options are being considered. Two main parameters can be used to classify the different PTES solutions: charging/discharging thermodynamic cycle and thermal energy storage system. Previous studies suggest that the most expensive components of the system are likely to be the compressor and turbine operating at high temperature, reaching in some configurations over 50 % of the total purchased equipment cost. As these machines operate under very similar conditions, it has been shown that a single reversible machine can be used, operating as a compressor during the charging process and as a turbine during discharge, with small efficiency penalties.

The objective of this paper is to assess the thermo-economic performance of different PTES configurations, including the effects of power capacity and discharge duration. Brayton, transcritical, and subcritical Rankine cycles with different working fluids are compared. Packed-bed rock and liquid thermal energy storage system are considered to store energy during the process. The cycle design for each configuration was optimized to minimize the levelized cost of storage by changing the pressure and temperature levels, turbomachinery performance, and pinch points temperature differences in the heat exchangers. Particular attention was paid to the estimation of cost for the turbomachines, as it can be argued to be the largest source of uncertainty. The results obtained with different turbomachinery cost correlations are compared. A novel cost correlation was also developed using a physics-based approach, adapted from an existing correlation for organic Rankine cycle turbines: the size of the machine and the number of stages are estimated, considering thermodynamic as well as mechanical limitations on the head difference that can be attained per stage. The novel contributions of this paper include the use of reversible turbomachinery in a techno-economic evaluation of PTES and the development of a new cost model for turbomachines.

Preliminary results indicate a strong impact of the cost correlation used, as different correlations result in different optimal configurations. Due to the necessity of pressurizing the entire storage volume, packed bed configurations were found to have a higher cost at long storage duration, while for shorter duration the savings on the heat exchangers became more significant.

Presenting Author: Simone Parisi Technical University of Denmark

Presenting Author Biography: Simone Parisi is a Ph.D. student at the Technical University of Denmark.
His research focuses on turbomachinery design for thermal energy storage applications, including concurrent cycle and machine optimization and reversible compressor-turbines.
His education includes a B.Sc. in Aerospace engineering and an M.Sc. in Mechanical Engineering, both earned at the Polytechnic University of Milan. During his M.Sc. he also graduated from the honors program of the Alta Scuola Politecnica.