Tutorial overview of flywheel energy storage in a photovoltaic power generation system

Of the various available energy sources, solar energy is one of the few that is simultaneously plentiful, easy to access, nonpolluting (although there is an environmental impact incurred in the manufacture of conversion equipment), and nondepletable (subject only to the longevity of the Sun). It holds promise for truly sustainable development. Despite the many benefits of using solar energy, its frequent unavailability makes it inappropriate for many applications. Consequently it is often necessary for photovoltaic (PV) systems to have an energy storage capability such that the excess output of the PV cells can be used at a time when solar energy is unavailable. Of the many schemes that have been developed to do so (based on mechanical, chemical, thermal, or magnetic principles, to name a few), the one chosen as the focus of this paper is that of kinetic energy storage in a rotating flywheel. Although this paper describes an integrated energy conversion and storage system, the emphasis is on the flywheel energy storage system since there is already a large body of literature dealing with PV generators