New review shows thermo-mechanical energy storage could revolutionize urban energy systems

A groundbreaking review by researchers from Shanghai Jiao Tong University, Imperial College London, and other leading institutions demonstrates that thermo-mechanical energy storage (TMES) technologies could transform how cities manage energy, achieving a coefficient of performance over 100% while overcoming limitations of conventional battery and pumped-hydro systems.

The study, published in Frontiers in Energy, systematically evaluates four major TMES technologies—compressed-air, liquid-air, pumped-thermal, and carbon dioxide energy storage—for their potential to deliver combined cooling, heating, and power (CCHP) from renewable sources.

As renewable energy generation accelerates globally, the need for large-scale, long-duration energy storage has become critical. While lithium-ion batteries and pumped-hydro storage dominate current discussions, they face significant limitations: batteries have relatively short lifespans and high lifecycle costs, while pumped-hydro requires specific geographical conditions. TMES systems offer compelling alternatives with minimal environmental impact, lifespans exceeding 30 years, and unique flexibility to simultaneously provide electricity, heating, and cooling.

"Traditional energy storage focuses solely on electricity, but modern communities need integrated energy solutions," said corresponding author Dr. Yao Zhao from Shanghai Jiao Tong University. "TMES systems can interact with both thermal and electrical demands, making them ideal for smart urban energy management."

The research team conducted an extensive review of over 100 studies, analyzing TMES-based CCHP systems across four categories:

1. Compressed-Air Energy Storage (CAES): Mature technology storing energy as high-pressure air, with compression heat recovered for heating and expansion for cooling
2. Liquid-Air Energy Storage (LAES): Stores air in liquid form at cryogenic temperatures, enabling high-density energy storage without geological constraints
3. Pumped-Thermal Energy Storage (PTES): Directly converts electricity to thermal energy via heat pump cycles, achieving exceptional roundtrip efficiencies
4. Carbon Dioxide Energy Storage (CES): Utilizes CO₂'s favorable thermodynamic properties and integrates with carbon capture technologies

The team compared system configurations, from basic designs to hybrid systems incorporating organic Rankine cycles and absorption refrigeration, analyzing performance across seasonal variations and operating modes.

The review reveals impressive performance metrics for TMES-CCHP systems:

• Roundtrip (power-to-power) efficiencies: 40% to 130%, with PTES systems achieving over 100% when integrated with external heat sources
• Overall trigeneration efficiency: 70% to 190%, far exceeding conventional power-only storage
• Levelized cost of energy: $70 to $200 per MWh, competitive with existing technologies
• Energy density: Up to 17.5 kWh/m³ for CO₂-based systems
• Carbon reduction potential: Up to 4,160 tons CO₂-equivalent annually for a 5 MW system

Hybrid systems showed particular promise. For example, CAES integrated with absorption refrigeration achieved 155% overall efficiency, while LAES-ORC-ARS hybrid systems reached 76% nominal roundtrip efficiency with 3-year payback periods. Joule-Brayton PTES systems with cascaded latent heat stores delivered heating from −140 °C to 550 °C and cooling simultaneously.

The review also identified AI's emerging role, with machine learning algorithms successfully optimizing system performance, predicting demand patterns, and enabling predictive maintenance—critical for managing the complex interplay between multiple energy vectors.

"TMES-based CCHP systems represent a paradigm shift from single-purpose electricity storage to intelligent multi-energy management," explained Dr. Zhao. "These systems can transform renewable energy fluctuations into stable, year-round heating, cooling, and power supplies for districts, industrial parks, and data centers."

Key implications include:

1. Geographical Flexibility: Unlike pumped-hydro, TMES systems can be deployed anywhere, crucial for urban and industrial applications
2. Sector Coupling: Enables integration of electricity, heating, and cooling sectors, maximizing renewable energy utilization
3. Economic Viability: 20% lower operating costs compared to conventional CCHP systems, with payback periods as short as 2.5 years
4. Scalability: Systems range from 10 kW building-scale to 300 MW grid-scale applications
5. Future-Ready: Integration with AI and power-to-gas technologies positions TMES as a cornerstone of future smart cities

The authors emphasize that while CAES and LAES are nearing commercial demonstration, challenges remain in developing high-temperature compressors for PTES and completing comprehensive economic analyses. The review calls for accelerated research in AI-driven control strategies and component optimization to unlock TMES-CCHP's full potential.

"Addressing these challenges will enable TMES-based CCHP systems to evolve into intelligent energy management systems for sustainable cities and districts," Dr. Zhao concluded, "playing a crucial role in the global energy transition."

The original review article "A review of progress in thermo-mechanical energy storage technologies for combined cooling, heating and power applications" is published in Frontiers in Energy (2025, Vol. 19, Issue 2) and available at https://doi.org/10.1007/s11708-025-0998-0