Losses of flywheel energy storages and joint operation with solar cells

It is possible to achieve stable levitation over a permanent magnet (PM) by using high temperature superconductor (HTS). This way, very low frictional coefficients can be achieved in the order of 10−6 or even smaller. This very small frictional coefficient makes flywheels with superconducting bearings adaptable as kinetic energy storages with very low losses. A system consisting of an HTS-based levitated flywheel as the energy storage unit and solar cells as the power supply was installed and investigated as a model of a viable variant of the mini power plant concept. A model was also developed to identify the frictional coefficient of such a superconducting bearing from spin-down measurements. As the different loss components have different speed dependence it is possible to separate them, and hence to give an approximation about the heat generated in the superconductor, which is a very important parameter for the design of the cooling system. The model was successfully applied to the flywheel energy storage (FES) unit of the above system.