Hybrids Without Batteries - 3/18/07

The hybrid vehicle has been the great success story of the high-mileage movement. Cars like the Prius get up to twice the mileage of the industry average partially by recovering energy that's lost as heat during braking, storing that energy in a battery, and reusing it later on. Yet today's most efficient hybrids can recover only 30 percent of that energy for reuse.

One radical idea under development at the Environmental Protection Agency's Advanced Technology Division is to get rid of the heavy batteries altogether.

The EPA has built a modified hybrid that uses a hydraulic system, not a battery, to store braking energy. When you press the brakes, the wheels drive a pump that compresses nitrogen gas, which is inert and inexpensive. When you accelerate again, that compressed gas runs the pump in reverse to help power the hybrid vehicle.

The hydraulic-hybrid system, scheduled to begin testing in two UPS trucks this month, with another to follow next year, promises to return at least 70 percent of the braking energy back to the wheels, which would lead to a 60 to 70% jump in fuel economy and a 40% reduction in emissions.

Back to the Hybrid Vehicles Index