LTS Flywheel - Long Term Storage-Flywheel: New approaches for increasing the economically usable storage time and safety

Development of the fundamentals for a Long Term Storage (LTS)-flywheel for decentralized storage of electrical energy (e.g. from wind or PV power plants), with a significant increase in storage time (goal: 12 hours) and safety, featuring low system costs. Therefore, the LTS-Flywheel is an essential contribution to the building of the future.

Short Description





Starting point/Motivation

Flywheels are a sustainable solution for decentralized energy storage. They offer longer life cycles (over 25 years), no requirement for maintenance, and usage of harmless, easily available materials, compared to other storage technologies, as for example accumulators. Flywheels, available up to now, are designed for short term energy storage in the region of minutes.

Contents and Objectives

The technological challenge within this research project is the development of fundamentals for a technology leap - Long Term Storage flywheel. Aim is a significant increase in storage time (12 hours at 80% load efficiency). Additionally, high reliability and low system costs are defined as project aims. This LTS-flywheel shall allow decentralized storage of electrical energy, for instance produced in in-house photovoltaic systems. Therefore, it is an essential contribution for developing the technological basis for the building of the future, especially the plus energy house.


For realizing the research aims, the project comprises the following focuses:

  • Exploratory focus on a full parametric simulation model
    Development of a full parametric simulation model for optimizing a flywheel regarding to a definable performance function: Definition of all required optimization parameters, determination of all interdependences, modeling of all flywheel components as MATLAB/ Simulink simulation models, optimized regarding to minimal computing time.
  • Exploratory focus on bearings
    Development of fundamentals of a magnetic bearing system with significantly increased energy efficiency compared to present magnetic bearing systems, and high reliability - cascaded hybrid magnetic bearing system with high reliability for radial and axial stabilization. This consist of a high efficient primary magnetic bearing with a permanent magnetic path for the application of static axial bearing forces and high efficient active magnetic bearings (AMB) for minimum energy consumption during normal operation with fully-adaptive control, an automatic switchover into a high performance AMB operation mode for start-up, interception of large external forces (e.g. earthquake) or emergency operation, as well as redundant high performance AMB systems in case of a power supply collapse or a malfunction within the primary high efficient/high performance AMB-system.
  • Exploratory focus on the rotor
    Development of fundamentals for an optimum rotor design with respect to high energy storage capacity, small necessary control inputs concerning the bearing, integration of all required bearing and motor/generator components and optimum utilization of material properties (young’s modulus, density, tensile strength, etc.) with respect to rotor configuration (eigenfrequencies, material combinations, winding and lamination technology, costs of materials and manufacturing, balancing, et cetera).
  • Exemplary optimization for 12h-energy storage for photovoltaic systems
    Exemplary optimization of the whole system as LTS-flywheel with 12h-storage time for photovoltaic systems using MATLAB/Simulink.
  • Experimental validation of the research results
    Validation of the research results, using a test arrangement based on the optimization results. Investigation of total power losses dependent on diverse operational states, behavior in case of component faults or sudden high bearing forces, power supply collapse.


Within the project, an innovation leap to much higher energy efficiency and therefore much longer storage times, higher reliability and security, as well as reduced system costs compared to commercially available flywheels has been be achieved.

The development of the LTS-Flywheel concept was been made possible by a global simulation, design and optimization approach in conjunction with a detailed modeling of all components as well as innovative solutions in the field of magnetic bearings, the rotor and the complete electronics. For almost all of the individual components new concepts had to be developed to meet the project goals at the best.

Further on, the development results within the project clearly demonstrate the high energy saving potential within the complete electronics chain (signal acquisition, control, power electronics, power supply).

Prospects / Suggestions for future research

The results of this project are the basis for the FFG-research project "Optimum Shape Flywheel". Within this project, further research regarding to optimal flywheel design and required manufacturing techniques is carried out.

Project Partners

Project management

Dipl.-Ing. Dr.techn. Alexander Schulz
Vienna University of Technology, department for mechanics and mechatronics

Contact Address

Technische Universität Wien, Institut für Mechanik und Mechatronik
Abteilung 4: Messtechnik und Aktorik
Dipl.-Ing. Dr.techn. Alexander Schulz
Wiedner Hauptstrasse 8-10/E325
A-1040 Wien, Österreich
Tel.: +43 (1) 58801 - 30313
Fax: +43 (1) 58801 - 30399