Energy Storage News

Pentadyne High RMP Composite Flywheel For Energy Storage

Pentadyne is the only company that I know of that has entered a commercial manufacturing phase for a carbon fiber composite, high RPM (56,000) energy storage flywheels. Here is some information from their web site:

The company shipped its first commercial production flywheel in 2004, and has sold and shipped more than 500 more since then.

Pentadyne Power Corporation, the world leader in flywheel energy storage systems, today announced that its fleet of installed products had exceeded a total of 3.5 million hours of reliable operation at end-user sites.

Three and a half million hours is equivalent to 400 operating years.


Pentadyne Power Corporation, a world leader in flywheel energy storage systems, announced that the Metropolitan Transit Authority of New York will use Pentadyne as the supplier of a 2.4 megawatt energy recycling system that will be used to capture, store and reuse braking energy of trains on a station of the Long Island Railroad.

Flywheels spin in a vacuum to minimize aerodynamic drag. Other systems use a constantly operating mechanical pump to maintain a rough vacuum. Instead, Pentadyne’s award-winning systems use a patented molecular vacuum sleeve on the flywheel shaft. The shaft speed combined with the sleeve’s helical grooves maintain the system’s high vacuum (<5 millitorr, or >99.9993% evacuated). This eliminates a mechanical point of failure, energy consumption and maintenance/downtime issues related to a continuously operating mechanical pump.

Pentadyne uses a synchronous reluctance motor-generator design that’s more energy efficient than permanent magnet types used in conventional flywheel systems. Permanent magnets are sensitive to heat and become less capable of operating to full capacity over time. This is particularly an issue in a vacuum environment. Pentadyne’s synchronous reluctance motor-generator design is somewhat more costly, but has no demagnetization issues even in temperature and vacuum extremes. This ensures performance of your Pentadyne system will not degrade over time.

Flywheels have many advantages over lead-acid UPS batteries, but energy efficiency hasn’t been one of them, until now. Thanks to the key technology aspects noted above, the standby energy consumption of a Pentadyne flywheel is a mere 250 watts, the same as the “float charge” consumption of a battery bank with similar capacity.

The rotating group spins at speeds at 25,000 (fully discharged) to 52,000 (fully charged) rpm.

Pentadyne is mainly selling flywheels for use in uninterruptible power supplies as replacements of or suplements to lead acid batteries. They are used for short duration backup power during outages. The total energy storage per flywheel is 528Wh. Since the power consumption on standby is 250 Watts, the flywheel consumes an amount of energy equal to its full storage capacity in just 2 hours and six minutes. Clearly such flywheels would not be useful for load shifting applications on a time scale of several hours (i.e. night time to day time).

Pentadyne's recent announcement of an agreement to install a 2.4MW flywheel system to capture and reuse braking energy on one station of the Long Island Railroad is interesting. The low rolling friction of trains makes them a potentially energy efficient alternative to rubber tired automobiles, but the need for numerous accelerations in an urban evironment with frequent rail stops negates part of this advantage. Capturing braking energy and reusing to accelerate the train back to speed is obviously advantageous from an energy consumption point of view.

September 13, 2009

Energy Storage News

rogerkb [at] energystoragenews [dot] com