Multi-Criteria Comparison of Commercial Scale ACAES With PTES for Grid and Energy Services

Abstract With the penetration of renewable energy sources into the market, energy arbitrage, i.e. to store energy from the grid at the time of low demand (thus at lower or negative cost) and release it into the grid at the time of high demand (at higher cost), is becoming common practice. To better harness the price curves in expanding renewable energy markets, large scale energy storage solutions with GWh of storage capacities, hundreds of MWs with flexible charging and discharging rates are required; utility scale storages should feature approximate charging time of 6h to 10h, shaving peak renewable energy production load from the grid in the daytime and 10+ hours discharging time at the night to meet the consumer electricity demands. Adiabatic compressed air energy storage (ACAES) is an high-efficient thermo-mechanical energy storage solution able to provide such large scale arbitrage services, which is currently close to commercialization thanks to the work of start-ups and companies around the world and that is laying its capabilities on already demonstrated potential by CAES systems in terms of high lifetime scalability, low self-discharge, long discharge times, relatively low capital costs, and high durability. On the other hand, pumped thermal energy storage (PTES) although still at a more infant technological development level, aims for the same category of storage solutions while providing additional benefits of no geographical constraints and no pressurized storage equipment in contrast to ACAES. This study compares the more technologically ready ACAES technology with emerging PTES technology for multiple techno-economic criteria with industrial constraints on commercially available turbomachinery. Both ACAES and PTES are modelled for providing 100MW of discharging power for 12 hours with 6 hours of charging targeting a round-trip efficiency of 70%. These constraints are then used to optimize the thermodynamic operating parameters of both the technologies for analyzing the specific cost of charging, storage and discharging equipment and performance parameters in terms of energy density, exergetic RTE and LCOS. The study shows that when compared to basic and advanced configurations, PTES shows lower LCOS, higher exergetic RTE than ACAES while the energy density is comparable. However, if looked at the specific cost of charging and discharging, ACAES is currently cheaper than PTES for both configurations. However, that may change with the presence of hot temperature compressors which may eliminate the need for an electric heater to reach the required operating temperature in PTES.