Optimisation of Geometric and Operational Conditions of a Flywheel Energy Storage System to Minimise Standby Losses

Flywheel energy storage systems (FESSs) have gained significant attention as a promising technology for effective harvesting, storage and redeployment of energy. This technology is used particularly in renewable energy applications where they help manage the intermittency and variability of energy output from renewable sources such as solar and wind by providing quick response, high power density, and cycling stability without the degradation issues associated with chemical batteries. This paper presents a comprehensive study on the optimisation of geometric and operational conditions of a FESS, with the view to reduce standby losses hence improving the overall efficiency of the system. The effects of the following parameters are investigated; the working fluid, operating pressure and geometrical configuration of the FESS casing, using Computational Fluid Dynamics (CFD) simulations to provide insights into the system performance characteristics. This study investigates the effects of concave and convex casing shapes compared to conventional uniform cylindrical casings. The use of these distinct shapes can lead to lower standby losses. In addition, the effects of the working fluid and the operating pressure are investigated. The effects of different working fluids including air, helium and carbon dioxide, on standby losses are studied at different operating pressures. The findings of this study highlight the significant potential for improving FESS efficiency through the optimisation of FESS casing design and the use of a suitable working fluid at optimal operating pressure. Windage losses can be reduced by 90% compared to the base model, allowing the FESS to function as a medium-duration storage solution rather than a short-duration, which is often a limiting factor when considering FESSs as an alternative solution to battery storage systems.