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Modern flywheel technology is based upon high tensile strength composite materials which can sustain the centripetal forces of very high speed revolutions (tens of thousands of rpm.) Energy is stored and extracted by electrically controlling the speed of revolution. High efficiency motor/generator designs and very low friction contact bearings or non-contact magnetic levitation bearings help keep the storage efficiency of a flywheel based system greater than 85%. Passive magnetic levitation based on Halbach arrays is a current research topic. Safe failure modes of the wheel are also a key to future widespread adoption. The important principle of flywheel physics is the the energy stored is proportional to the square of the rotational speed. Flywheels offer many times higher energy storage per kilogram than conventional batteries, and can meet very high peak power demands. A flywheel unit could reasonably be expected to last at least ten years with no maintenance, but as the technology is not very old the optimistic useful lifetime predictions are derived from mathematical models of the component technologies, not from field data.
Progress in the field has been rapid in the last decade, so search results dating from the 1980's or earlier have been omitted from the listing below. There are three applications of flywheel technology: stationary power storage as in uninterruptible power supplies (UPS), automotive power management in an electric or hybrid electric car, and spacecraft attitude control. As both stationary and mobile power sources could be useful on the moon, links to both space and a few automobile applications have been included here. Links concerned primarily with spacecraft attitude control are included here if the flywheels on a spacecraft are dual-use for both power and attitude control, and because many of the other environmental factors are similar to the lunar surface.
Reference to offline sources
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