Each stationary “wayside” EnerGstor unit incorporates an ultracapacitor array that is capable of storing up to two kilowatt hours of electrical energy generated by a rail vehicle’s braking energy recuperation system.
Recuperative braking is accomplished by running the vehicle’s electric motor backwards to stop the vehicle with the motor’s resistance. An electric motor running backwards also acts as an electric energy generator or dynamo that converts kinetic energy into electrical energy that can be stored for future use.
The EnerGstor system offers multiple benefits to rail system operators, including:
• A 20 to 30% reduction in grid power consumption.
• Improved regulation of line voltage across a multi-stop rail system.
• Significant reduction in brake maintenance expense.
• Backup power to enable vehicles to reach a station in the event of a grid power failure.
The ultracapacitor-based energy storage unit captures and stores energy that otherwise would be wasted in a conventional, friction-based, braking system. Ultracapacitors also provide extremely long operational life in the demanding public transit environment and function normally at extreme temperatures, contributing to system reliability and reduced operating expenses.
Maxwell ultracapacitors are powering more than 4,500 hybrid transit buses currently in service worldwide, and are being employed in several other transportation applications, including a stop-start idle elimination system developed by Continental AG for micro hybrid diesel automobiles now being produced by PSA Peugeot Citroën in Europe.
Unlike batteries, which produce and store energy by means of a chemical reaction, ultracapacitors store energy in an electric field. This electrostatic energy storage mechanism enables ultracapacitors to charge and discharge in as little as fractions of a second, perform normally over a broad temperature range (-40 to +65°C), operate reliably through one million or more charge/discharge cycles and resist shock and vibration, according to the company.
Maxwell offers ultracapacitor cells ranging in capacitance from one to 3,000 farads and multi-cell modules ranging from 16 to 125 volts.