In my last posting about flywheel energy storage I speculated that since steel flywheels appear to be beating out carbon fiber composite flywheels in UPS (Uninterruptible Power Supply) systems, it might turn out that steel flywheels would be also be a better choice for grid frequency regulation applications. (Frequency regulation, by the way, is actually power regulation. The grid is set up so that mismatches between load and generation manifest themselves as changes in the frequency of the AC current.) A startup company called Amber Kinetics, which originated from a Stanford University Cleantech Entrepreneurship class, is targeting exactly this application with flywheel rims made out of steel wire (See this presentation).
Amber Kinetics claims that its steel wire flywheel rims are twenty time cheaper (presumably per kWh of energy storage) than rims made out of carbon fiber composites. However the balance of system costs associated with the magnetic bearing, and the motor generator are significant. UPS applications which currently use steel flywheels only require about 15 seconds of energy storage which is sufficient to allow a diesel generator to power up. According to this document frequency regulation includes accommodating power fluctuation for time periods up to ten minutes. This longer energy storage time puts more severe economic limits on flywheels used for this application compared to UPS applications.
This DOE report on the Amber Kinetics demonstration project which it is helping to fund claims that improvements in the magnetic bearings, low-cost rotor, and high-efficiency motor generator are all being pursued in order to reduce costs. Since it is far from clear that any low hanging fruit remains in the areas of magnetic bearing design and motor/generator design I think holding ones breath waiting for this project to produce and economic winner is probably not a good plan.
May 1, 2013Energy Storage News
rogerkb [at] energystoragenews [dot] com