A HIGH-EFFICIENCY ELECTROMECHANICAL BATTERY

In our increasingly electrified society there is a growing need for efficient cost-effective means for storing electrical energy. The electric auto is a prime example. Storage systems for the electric utilities, and for wind or solar power, are other examples. While electrochemical cells could in principle supply these needs, existing E-C batteries have well-known limitations. This article addresses an alternative-the electromechanical battery (EMB). An EMB is a modular unit consisting of an evacuated housing containing a fiber-composite rotor. The rotor is supported by magnetic bearings and contains an integrally mounted permanent magnet array. Recent developments in high-strength fibers, in permanent-magnet materials, and in solid-state power electronics open up new possibilities, allowing the design of small (1 kW-h) modular EMB's for full- or hybrid-electric vehicles, and larger size modules (25 kW-h), for a variety of stationary storage needs. The article addresses design issues for EMBs with rotors made up of nested cylinders. Issues addressed include: rotational stability, stress distributions, generator/motor power and efficiency, power conversion, and cost. An important conclusion; the use of EMB's in electric autos could result in a five-fold reduction (relative to the IC engine) in the primary energy input required for urban driving, with a concomitant major positive impact on our economy and on air pollution.