Mechanical design of flywheels for energy storage: A review with state-of-the-art developments

For years, engineers and designers have capitalized on electrochemical batteries for long-term energy storage, which can only last for a finite number of charge–discharge cycles. More recently, compressed hydrogen is being scrutinized as a large-scale storage medium but this poses the risk of spreading high-pressure vessels with inflammable content. Historically, flywheels have provided an effective way to smooth out speed fluctuations in irregular achines and mechanisms. With advancements in composite materials, magnetic bearings, and mechatronic drives, flywheels have become the subject of extensive research as power storage devices for mobile or fixed installations. Flywheel energy storage systems are considered to be an attractive alternative to electrochemical batteries due to higher stored energy density, higher life term, deterministic state of charge and ecological operation. The mechanical performance of a flywheel can be attributed to three factors: material strength, geometry, and rotational speed. Focusing on the simple relationship between these variables, this paper reviews the literature of flywheel technology and explores the merits of four simple but unconventional flywheel configurations that have not been examined so far. Two geometries assume the use of monolithic isotropic materials two solutions are based on the use of high-strength strips or tapes wound up to form a multilayered structure.