GE demonstrates dual battery system for electric buses; pairing high-energy density sodium battery with high-power lithium battery optimizes performance and lowers cost
|Electric bus with dual battery system. Click to enlarge.|
The hybrid systems research team at GE Global Research has successfully demonstrated a dual battery system for an electric transit bus, pairing a high-energy density sodium metal halide battery with a high-power lithium battery. A123Systems—which is a partner in the project, and in which GE holds a significant stake (earlier post)—provided the Li-ion power battery. GE developed a computerized energy management system to manage the vehicle power needs between the two types of battery packs.
The research is being done as part of a $13-million research project GE is engaged in with the Federal Transit Administration (FTA) and Northeast Advanced Vehicle Consortium, funded under the National Fuel Cell Bus Program. Currently, the bus has a top speed of 50 mph (80 km/h) and about a 60-80 mile (97-129 km) range under idealized conditions. The ultimate target is 62 mph (100 km/h) and a real-life 100-mile (161-km) range, while traveling a transit bus route with its multiple stops and starts, according to Lembit Salasoo, principal investigator on the FTA Hybrid Transit Bus project.
The combination of the two systems could reduce the total battery system cost for such a vehicle by up to 20% compared to a single battery system, GE said.
While significant advances in battery technology have been made, further reductions in the size and cost of batteries will be needed to enable the widespread adoption of electric vehicles. GE researchers believe a dual system with high power and energy storage capacity could achieve the optimal electric driving range and acceleration requirements at a more practical size scale and cost for larger vehicles.
GE will conducting another bus demonstration for the project next year, in which it will be using its new sodium battery (earlier post) and a new modern, advanced composites lightweight bus.
We’re entering a decade of unprecedented activity and developments in electrified transportation. With heavier vehicle platforms, both energy storage and power are a premium to deliver optimal vehicle performance, but the exact needs can vary based on a vehicle’s size and drive cycle. The beauty of our dual battery system is that it can be scaled to deliver just the right combination of power and storage.—Lembit Salasoo, Senior Electrical Engineer and Principal Investigator
Many of the 843,000 buses registered in the US (including most of the 63,000 transit buses and 480,000 school buses) travel less than 100 miles per day. Enabling more of these buses to transition to an all-electric, zero emissions platform would significantly reduce CO2 emissions and petroleum fuel consumption.
Most types of batteries today come with a trade-off between power and energy storage. Lithium-ion batteries can provide a lot of power for acceleration, but are not optimized to store energy for extended driving range. Sodium batteries are on the opposite side of the spectrum. They store large amounts of energy, but are less optimized for power. GE’s dual battery combines the best attributes of both chemistries into a single system. In the hybrid transit bus demonstration, the lithium battery focused on the high power acceleration and braking, while the sodium battery provided an even electric power flow to extend the bus range.
In addition to optimizing performance, the key cost advantage of a dual system is that it provides flexibility to integrate less expensive battery chemistries without having to increase the size of the battery to address a vehicle’s power and energy storage needs. A single chemistry battery system would require a more costly scale up in the size of the battery to achieve the same result.
The development of a dual battery system and partnership with the FTA is a key part of GE’s growing hybrid and electric technology portfolio. GE is actively exploring partnership opportunities across the electric vehicle value chain through its Licensing business to commercialize its dual battery technology.
GE also is developing new technologies and products to support the integration of plug-in hybrid electric vehicles (PHEV) and electric vehicles (EV) into the electric grid.