The Graz University of Technology has led a project team to develop a flywheel storage system prototype, FlyGrid, that can store electricity and deliver it quickly using innovative charging and storage solutions. The prototype has been integrated into a fully automated fast charging station, designed to store power generation surpluses for times when renewables are not supplying electricity, and to increase grid stability and the charging infrastructure.
The Flywheel Storage System
FlyGrid is a flywheel storage system that has been developed by a project consortium consisting of universities, energy suppliers, companies, and start-ups. After several months of testing at the University of Leoben, the flywheel storage system has now been put into operation at Energie Steiermark, where it can be further improved under real conditions. The prototype’s buffer storage has an energy content of five kilowatt-hours and offers a charging capacity of 100 kW. Larger storage volumes are also possible due to the modular design.
Although flywheel storage technology is one of the oldest energy storage forms, it was necessary to adapt the subsystems and components to new requirements. A rotor—the eponymous flywheel—is accelerated to a high speed by an electric motor, and the energy is stored as rotational energy. The energy is recovered by the rotor giving off its rotational energy to a generator. The entire development and production took place in Austria.
The development partners paid special attention to the rolling bearings, with rolling bearing manufacturer myonic playing a leading role. They have to withstand speeds of up to 30,000 revolutions per minute with a rotor weight of 160 kilograms. High-strength carbon fiber was used for its manufacture since the amount of energy that can be stored in the rotor is limited by the centrifugal force.
Project partner FWT has developed a special manufacturing process for the carbon fiber composite rotor. The rotor is accelerated by a loss-optimized, synchronous reluctance motor, which was developed by the company Thien eDrives. This electric motor technology was chosen because it achieves a high degree of efficiency and does not require magnets or rare earths. However, the motor consumes energy to maintain the charge, which means that the storage unit discharges over time and is empty after about 25 hours.
FlyGrid should, therefore, be seen as a short-term storage system that is only viable if energy is supplied and removed frequently. The system is packed in a specially developed safety housing. A significant advantage of FlyGrid is its expected long service life, which, unlike batteries, is not dependent on the number of charging cycles or age.
Applications of FlyGrid
In addition to energy storage and delivery, the project developed a holistic concept around storage that also takes into account aspects of energy supply, grid load, and charging infrastructure. This is reflected in FlyGrid’s intended areas of application. Among other things, local volatile sources such as PV systems are to be integrated, whose energy can be stored not only for charging but also for feeding high power into the grid. FlyGrid could also be used as a mobile fast-charging box, e.g., for electrified construction machinery. In the field of charging technology, project partner easelink contributed its fully automated charging system Matrix Charging.
“The increasing electrification of mobility and also of industry as well as the expansion of volatile renewable energy sources are a challenge for our electricity grids. Therefore, it is important to offer solutions that on the one hand relieve the electricity grid and on the other hand facilitate the use of e-mobility,” explains project leader Armin Buchroithner from the Institute of Electrical Measurement and Sensor Systems at Graz University of Technology (TU Graz).
“In addition to solutions such as chemical batteries or pumped-storage power plants, FlyGrid’s flywheel storage offers a long-lasting system that provides high performance. This makes FlyGrid a useful addition that supports the shift to renewable energy on a smaller and larger scale,” he says.
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