okay.. for a 20MW system, what are the specifics of a flywheel system vs a conventional system, which I assume is a bank of lead-acid batteries. Energy capacity? Cost? Size? Lifetime?
update: a quick search found this flywheel system by the former Beacon Power:
Beacon Power will design, build, and operate a flywheel energy storage frequency regulation plant at the Humboldt Industrial Park in Hazle Township, Pennsylvania. The plant will provide frequency regulation services to grid operator PJM Interconnection. Beacon’s technology uses flywheels to recycle energy from the grid in response to changes in demand and grid frequency. When generated power exceeds load, the flywheels store the excess energy. When load increases, the fly- wheels return the energy to the grid. The flywheel system can respond nearly instan- taneously to an independent system operator’s control signal at a rate 100 times faster than traditional generation resources. The system does not burn fuel and has zero emissions. The Beacon Gen4 flywheel is designed with 100 kW of output and 25 kWh of energy. Two hundred flywheels will be connected in parallel to provide 20 MW in capacity and can fully respond in less than 4 seconds. The plant can operate at 100% Depth of Discharge with no energy degradation over time and can do so for over 150,000 full charge/discharge cycles. The flywheels are built to last 20 years or more. Virtually no maintenance is required in the mechanical portion of the flywheel system. Flywheel technology has been successfully tested on live grids at scale power in New York and California. The technology achieved system availability of over 97 percent, higher than the average for conventional generators performing frequency regulation. It has been deployed at multi-megawatt scale under New England’s Alterative Technologies pilot program. The site has the potential to support the distribution system that connects a nearby solar project to the grid.
another update: also from SmartGridNews, this blurb about a 20MW storage system from A123:
A123 Systems a developer and manufacturer of advanced Nanophosphate lithium ion batteries has announced that AES Gener will order 20MW of A123′s advanced energy storage solutions for a spinning reserve project in Northern Chile.
A commercial 12MW spinning reserve facility is operational in AES Gener’s Los Andes substation which is in Chileâ€˜s Atacama Desert, it was AES first implementation of A123 energy storage technology.
Chris Shelton, president of AES Energy Storage said, “The project will utilize A123 lithium-ion batteries to supply a flexible and scalable emissions-free reserve capacity installation for AES Gener. We are excited to work with A123 to improve the performance and reliability of the Chilean power grid”.
The A123′s lithium-ion energy storage systems are highly scalable design which consists of modular energy storage racks, power electronics, communications and controls software. The storage systems design and technology enables grid operatorâ€™s better control for frequency regulation, spinning reserve and other ancillary services.
Robert Johnson, vice president of the Energy Solutions Group at A123, said “Projects like this and others we are working on demonstrate the commercial viability of our advanced energy storage capabilities, and we expect the technology to play an integral role in increasing the efficiency of ancillary services and enabling the wide-spread integration of renewable energy”.
A123 with AES Energy Storage is also expected to complete an energy storage facility in Johnson City, NY sometime in 2011. The new system will supply 20MW of emissions-free reserved capacity to the power market operated by the New York Independent System Operator.
A123 is the largest producer of lithium ion batteries for ancillary services for the power grid and its lithium-ion energy storage systems facilitate the integration of renewable energy sources which offers a cost-effectively hybridize power plants to improve grid stability.
That's a lot of text.. sorry. It does sound like both systems are scaled for utilities, and not for home power. Both articles are a couple of years old, and both companies are now out of business or sold off to private equity companies (is that right?). Neither seems to be economically viable at this point, based on the evidence. Unfortunately, neither blurb provides the basic metrics that would allow you to compare the relative performances of the two technologies.