Mechanical storage includes storage methods such as compressed air energy storage (CAES), liquid air energy storage (LAES) and flywheel. These solutions can provide frequency balancing by producing electricity with a rapid response time. Flywheels have the most rapid response time and can provide inertia as well as other immediate frequency balancing products. CAES involves compressed air which can be expanded and used to drive a turbine that creates electricity. LAES entails cooling down air until it becomes liquid, which also can expand and be used to drive a turbine that creates electricity. CAES and LAES can provide both frequency balancing, congestion management and adequacy, whereas flywheel is suitable only for frequency balancing.
Components & enablers
State of the art in application and research
The projects address different technologies.
- Story: A use case where compressed air is stored in containers in combination with tidal energy production.
- ADELE: A project the focus of which is how adiabatic compressed-air energy storage for electrical supply can increase its efficiency and response time.
- CryoHub: Investigates the potential of large-scale LAES at refrigerated warehouses and food factories to use the stored energy for providing both cooling on site and electrical generation during peak demand periods.
- Hybridised LAES: Demonstration facility that uses peak power to liquefy air by cooling it down. The liquid air is then stored in insulated tanks for later use.
- KryoLens: Increase of the TRL of the bulk energy storage technology for LAES.
- Schwungrad Engine – Rhode Hybrid Test Facility: The Schwungrad Engine will develop and perform the operational testing of a flywheel energy storage plant (4 × 150 kW units).
- OSMOSE demonstrates a flywheel as part of a hybrid storage solution to provide synthetic inertia.
There are two CAES plants in operation today, but the efficiency is only 54%. ADELE aims to improve this to 70%.
Technology Readiness Level
LAES: TRL 7
Hybridised LAES had a demonstration plant which showed that the plant could provide short term operation reserve. They found that the start-up time needs to increase because fast-reacting short term storage is most important for power plant utilities.
CAES: TRL 7
There are two CAES plants that are in operation today, but the efficiency is only 54%. ADELE aims to improve this to 70%.
Flywheel: TRL 9
Schwungrad Engine will develop and perform operational testing of a flywheel energy storage plant (4 × 150 kW units).
Flywheel is a mature technology which is completely introduced in the industrial market. The TRL is therefore 9; however, prototypes such as the Schwungrad Engine aim at improving the technology.
OSMOSE applies flywheel technology as part of a demonstrator (WP4) to optimise flexibility services (synthetic inertia, frequency balancing and congestion management) from a hybrid storage solution which also includes battery storage and supercapacitors.
Current focus of R&D and research gaps
The start-up time needs to increase because fast-reacting short term storage is most important for power plant utilities. There is also potential in increasing the efficiency and reducing the costs.
More research on technology is required for it to be competitive with other energy storage solutions.
 EASE – EERA Joint Recommendations – European Energy Storage Technology Development Roadmap Towards 2030. 2013 [Link1]
 REEEM. Innovation Readiness Level Report – Energy Storage Technologies. 2017. [Link1]
 Highview power [Link]
 KryoLens [Link]
 RWE. ADELE – Der adiabatische Druckluftspeicher für die Elektrizitätsversorgung (Adiabatic compressed air energy storage)
 Schwungrad Engine – Rhode Hybrid Test Facility [Link]
 OSMOSE [Link]