Source: U.S. Air Force

THE AIR FORCE Research Laboratory’s Space Vehicles Directorate is conducting an experiment to demonstrate the use of flywheels to provide power for satellites. For years, flywheels have been used on satellites to provide orientation stability. The idea behind this recent Air Force test is to see if satellites could get double duty out of flywheels to replace spacecraft batteries.

The reasons for wanting this change are compelling. Project engineers believe that flywheels can deliver as much as 10 times the power level of battery-based energy systems and can operate on-orbit for about twice as long as chemical batteries.

Not surprisingly, such characteristics make flywheels attractive to the energy industry, too.

For years, the Electric Power Research Institute has been interested in flywheels for their ability to smooth over short-term outages and power sags.

And increasingly, electrical grid and power utility organizations are evaluating ways to use flywheel technology to improve power reliability and quality, as well as to provide an alternative backup power source for remote facilities and sites.

For example, in March, the U.S. Department of Energy and New York State Energy Research and Development Authority installed a flywheel-based system into the electrical grid in Amsterdam, N.Y.

The purpose of this joint project is to evaluate and demonstrate the use of flywheel-based systems in improving the quality of electrical power by automating frequency regulation.

"With our growing demand for electricity, it is extremely important to develop new and more advanced technologies that can help improve the performance and reliability of our electric grid," said Peter Smith, president and CEO of NYSERDA.

Commenting on the project, Imre Gyuk, head of the DOE’s energy storage program, said: "[The project] has brought us a huge step closer to proving the effectiveness of flywheels for frequency regulation."

The flywheel systems in this case were provided by Beacon Power, which is among a handful of vendors that includes Active Power, AFS Trinity, Pentadyne, and Precise Power Systems, who are all targeting utility companies with their flywheel systems.

In many cases, flywheel systems are being eyed as a complementary technology to batteries or diesel backup generators. Flywheel systems would provide nearly instant power when a disruption or power sag occurs.

When used in this manner, flywheels might extend the life of installed battery systems.

The reason deals with the strain placed on batteries when used to provide a quick, powerful burst of voltage. The effect is called coup de fouet or battery whiplash, which involves the sudden voltage drop a battery experiences when being discharged quickly.

According to EPRI, 98 percent of all voltage sags and outages last less than 10 seconds. The 2004 NASA Flywheel Batter Project noted that if flywheel systems are used in parallel with batteries, the flywheel systems could handle these short-term voltage instabilities, greatly reducing the number of battery whiplash incidences. In this way, batteries would be saved for longer term outages, which would significantly increase battery life.

Another use of flywheels is as a battery-system replacement, particularly in remote power distribution scenarios, such as backing up the power delivered to a cell-phone tower. In deployments to remote locations, battery-based systems are hard to maintain; a flywheel system would be better suited for the job, because it does not need as much maintenance.

Additionally, flywheel systems are being eyed for use in power grids and other utility applications where temperatures might be an issue. Flywheel power systems can operate in a wide range of temperatures, which is not the case with chemical batteries.

One factor that has limited the use of flywheel systems is the cost. Typically, flywheel systems are about 50 percent higher in price as comparable performance-battery systems. However, flywheel systems are becoming more appealing as companies take into account long-term issues, such as a product’s life span, maintenance, and environmental factors, which include the disposal of lead batteries.