Engineers on Dec. 13 began testing a bus equipped with a new hybrid energy system that will significantly cut the cost to buy and operate zero-emission mass transportation vehicles.
At the heart of their work is an energy management system that mixes power output from GE’s new Durathon battery, a lithium battery and a hydrogen fuel cell.
“With this system, we are bringing together a battery that supplies power, a battery that provides a lower amount of energy longer and a fuel cell that creates the base load of electricity to operate the bus,” says Tim Richter, Systems Engineer in the Electric Propulsion Systems Lab at GE Global Research. “It’s all centered on the system that manages power, energy and the fuel cell all in an intelligent way.”
Current fuel-cell-powered buses must include batteries to provide power for acceleration. Up to today, though, hybrid systems have not run as efficiently as they can because they use lithium-based batteries, which often produce more energy than needed and drain quickly. This limits a bus’s range to around 50 miles and increases costs by requiring larger, more expensive fuel cells.
The problem is that modern batteries can only be built to provide either large amounts of power for a relatively short time or smaller amounts over a longer time. But that 50-mile range in current electric buses just isn’t good enough: some 63,000 transit buses and 480,000 school buses in the U.S. travel less than 100 miles per day.
Increasing the range and decreasing the initial investment cost of zero-emission electric buses and other larger, heavy-duty trucks would help move them into fleets while dramatically reducing CO2 emissions and fossil-fuel consumption.
That’s why GE has been exploring ways to synergize the benefits of its sodium-based Durathon technology, which can store a large quantity of energy but isn’t optimized for power, with powerful lithium batteries in hydrogen fuel-cell-powered electric buses.
Richter says the new management system, GE’s Ecomagination-qualified Multi-Energy High Voltage Energy Management Architecture, has been created to manage the bus’s power sources and provide the energy it needs when it needs it. This innovation cuts inefficiencies and allows engineers a design degree of freedom.
The energy management technology is a combination of hardware and software all in one box. DC converters boost low-voltage electricity to power the bus’s motor while the software controls the converters to get the best out of the different sources of energy.
He believes this more tailored design approach will allow engineers to scale back the size of costly hydrogen fuel cells. Decreasing the cell’s size means potentially lowering a bus’s initial cost by 50 percent. Better power management also means long-term savings in operating the vehicle.
“GE’s Multi-Energy High Voltage Energy Management Technology releases vehicle designers from the traditional constraints of single battery configurations,” he says. “Combined with two or more batteries or energy devices, the system allows GE to enable various power-to-energy configurations that match the vehicle needs.”