An effective energy storage system can be used in a variety of ways to improve the utility factor of electric generating plants while greatly reducing their requirement for fossil fuels. An optimum energy storage system would have the following characteristics: installed and operating costs are comparable to equipment which it replaces; design lifetime is 30–50 years; and the system is available over a size range of nearly one million to one without significant compromises in cost effectiveness. Thus such a system could have a large variety of on-site applications, from the smallest electric vehicle to the largest utility's diurnal peaking unit. The system must have size and operating characteristics that permit its being used at any desired location, whether urban, suburban, or rural. It must be capable of automatic remote control and freedom from maintenance. It must have negligible effect on local ecological conditions. It must be capable of being produced in the required quantity without creating a national shortage of strategic materials. It must be available to industry within five years. A modern flywheel made of anisotropic materials appears to be capable of satisfying these requirements better than any energy storage concept currently being considered.