REVIVED INTEREST in flywheel cars. “The automakers Volvo and Jaguar are testing the possibility of using flywheels instead of batteries in hybrid electric vehicles to aid acceleration and help engines operate more efficiently. The devices could reduce fuel consumption by 20 percent and would cost a third as much as batteries. Volvo will begin road-testing a car with the technology this fall.” It’s an old idea, but technology has improved. “”Most hybrids with batteries provide a 15- to 25-kilowatt boost of power. The flywheel can deliver 60 kilowatts in a way smaller package.” With some catches.