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XALT Energy's modular sub-pack is configurable from 7.1 to 11.4 kW·h. (image: XALT Energy)

Making the case for battery-electric fleet power

Battery-electric power is drawing more and more applications to commercial and heavy-duty fleets as the zero emission technology edges closer to a tipping point.

“We’re not at critical mass in any market yet with battery-electric,” said Rick Herndon, Chief Executive Officer of Voltabox of Texas Inc., a manufacturer of Li-ion battery systems.

One market undergoing dramatic change is commuter buses. “All the big players recognize they have to have electric, especially for municipal applications,” he said. Herndon and other technology experts recently spoke with Truck & Off-Highway Engineering during The Battery Show and Electric & Hybrid Vehicle Technology conferences in Novi, MI.

Electrifying transit buses

While electric public transportation buses still reflect relatively small numbers, substantial growth is projected around the world.

In India, for example, the goal is to have 300,000 electric transit buses by 2030. “India’s electric mass transit wants are driven by a government initiative aimed at reducing fossil fuel consumption,” said Adrian Schaffer, Senior Vice President of Sales and Business Development for Longmont, CO-based UQM Technologies. “There are opportunities in India and other regions; I think the key is to start thinking about how we create partnerships to grow the battery-electric market.”

More than 800 electric transit buses are in-service or on-order throughout the U.S. as of September 2017, according to Fred Silver, Vice President of CALSTART, a non-profit organization headquartered in Pasadena, CA.

“We’re pretty much covering the waterfront when it comes to the different kinds of bus platforms available in the U.S.,” said Silver, noting that the electric products range from microbus to double-decker transit buses.

Proterra’s Catalyst portfolio—the FC, XR and E2 Series—of 40-ft (12-m) electric buses reflects different curb weights and driving ranges. “The innovative part is that all of our Catalyst buses use the same physical space for the battery packs, so there’s not a unique underbody for each bus,” said Dr. Gary Horvat, Chief Technology Officer for Burlingame, CA-based Proterra.

As the newest bus in the product lineup, the Catalyst E2 claims the longest driving range of any electric transit bus, the company claims. The vehicle’s LG Chem developed Li-ion cells are housed in a liquid-cooled battery pack with an energy density of 160 W·h/kg and 260 W·h/L, regarded as the highest in the heavy-duty industry. E2’s energy storage system accounts for approximately 20% of the vehicle’s curb weight: 29,850 to 33,060 lb (13,540 to 15,000 kg).

“Because of where our battery packs are packaged, there’s a low center of gravity. That means improved performance. The bus has better handling for the driver because the battery pack weight is in the center, under floor between the axles, rather than in the rear of the bus,” Horvat said.

Battery pack modularity

Battery pack modularity is viewed as an essential element to accommodate the inevitable changes in technology, according to Martin Klein, Vice President of Engineering for Midland, MI-based XALT Energy.

“Heavy-duty fleet managers want to know year-over-year that the same base product can be updated,” said Klein. “The ability for an operator to upgrade as soon as new technology, including cell and controls, comes online is very important.”

XALT Energy’s battery sub-pack provides an easy-to-install solution for its customer base, which includes heavy-duty trucks, construction vehicles, and transit buses. “Our sub-pack has a cast aluminum enclosure, and that’s important as the large format batteries are undergoing heavy usage with some buses on 18-hour drive cycle schedules on a daily basis,” Klein said.

The cast aluminum enclosure enables bolt-on features, reducing the overall parts count. Inside-the-pack considerations include cell tabs welded to the bus bars, and direct liquid cooling of the cell face. “We don’t use passive cooling plates because that would add mass to the pack and such plates are much less efficient,” said Klein. Depending on the cell, the energy storage in the 90-V battery sub-pack ranges from 7104 to 11,482 kW·h.

“If an operator wants to change from a short-run bus with frequent stops to a long-range bus, it’s just a swap out of the battery core. We update the voltage, the curves, and the calibrations and the pack is ready to go with the same cables, same connectors, same mounting locations, same battery management system,” said Klein, noting that the pack is designed to last for 12 years.

XALT’s available remote monitoring system can detect problems during in-vehicle operation. “In one example, we noticed that a customer’s cell string was down. We called them before they knew of the problem,” Klein said, citing a loose vehicle connector as the culprit. “Real-time monitoring can pinpoint issues quickly and that’s important, especially for new entrants into the electric vehicle market.”

Forklifts ripe for Li-ion

For electric forklift applications, lead-acid batteries remain the popular choice, according to Mil Ovan, President and Chief Marketing Officer of Woodridge, IL-headquartered Navitas Systems. “The forklift market is the largest non-automotive market by dollar volume for lead-acid batteries, representing about $2 billion a year in North America,” said Ovan.

It’s a meaty market of opportunity that Ovan and others say is ripe for Li-ion battery technology.

“As the temperature plummets, the ability for lead-acid chemistry to react and provide energy slows down. So as the temperature falls, like in a food distribution warehouse, there’s more runtime available with a Li-ion battery-powered forklift,” Ovan said.

In a “sit-down” Class 1 forklift application, a lead-acid battery can weigh up to 4000 lb (1814 kg), about double that of Li-ion batteries. Lead-acid batteries also require about eight hours of charging time, much longer than the fast-charging time for Li-ion. It also takes about eight hours for lead-acid batteries to cool down before a return to service. In short, the drawbacks associated with lead-acid have opened the door for Li-ion batteries.

“Eventually you’ll see the forklift manufacturers take advantage of the fact that a Li-ion battery is smaller and lighter weight,” said Ovan, noting that a change in battery chemistry can elicit new forklift designs that reduce the possibility of tipping, rolling, and other vehicle instabilities. “You can lower the center of gravity if you’ve relaxed the lead-acid battery box constraint because you can put the energy storage where you want,” he said.

Proponents of battery-electric applications say the technology is absolutely ready. “So now the discussion needs to be about commercial viability to determine where the value proposition is within the market segments around the globe,” said Herndon.

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