Ivan, List,
Correction,it was the Lawrence Livermore Labs that did the research in the mid-1990s using a bank of very high speed composite flywheels as power storage.
The flywheels incorporated rare earth magnets to get the power in and out and were run on air bearings, with the flywheel in an evacuated vessel IIRC. Turn around efficiency (energy out / energy in ) was stated as 99% compared to about 65% for a lead acid battery.
I found this Livermore paper for some of the details, but I think the original article that got me interested was in the Scientific American October 1997.
http://www.osti.gov/bridge/servlets/purl/358801-vtzl8B/webviewable/358801.pdf Flywheels in Hybrid Vehicles; October 1997; Scientific American Magazine; by Rosen, Castleman; 3 Page(s)
The search for an alternative to the internal-combustion engine used in today¿s cars is motivated by two societal concerns: the need to reduce fossil-fuel consumption and the need to reduce air pollution. Unfortunately, most car buyers do not make their purchases based on these criteria. Instead, when looking for a new automobile, most consumers consider issues such as cost, safety, performance and fuel efficiency. (This last factor does, of course, have an effect on fuel consumption and pollution, but it is rarely a car buyer¿s primary concern.)
In 1993 one of us (Rosen), along with his brother, Benjamin, founded Rosen Motors with the goal of producing a new type of powertrain for cars that would not only address concerns about pollution and fuel efficiency but would also be something that consumers would actually want to own.
http://www.sciamdigital.com/index.cfm?fa=Products.ViewIssuePreview&ISSUEID_CHAR=55FFD523-BFC2-4006-87AB-B49A4B9B4A1&ARTICLEID_CHAR=40A5048D-1AE0-4AED-B8B7-1472C964FBE
