Walmart embraces green trucking
By Allen Penticoff
[dropcap]While[/dropcap] doing some research for my presentation at the IREA Renewable Energy Fair, I came upon some interesting news regarding advances in large truck propulsion.
There is much development going on in semi-tractor trailer propulsion and design, but for this story, I’ll limit what is happening with the Walmart Advanced Vehicle Experience (WAVE) prototype design.
Walmart operates one of the largest private fleets of trucks in the nation. In 2005 Walmart stated it intended to achieve fleet fuel efficiency increases of 100 percent by 2015. As of 2016, they have increased fleet efficiency by 84 percent. They also have a goal to operate their massive fleet entirely on renewable biofuels.
Walmart has moved its distribution centers nearer to the major metropolitan centers it serves. This not only reduces the number of miles that the trucks drive daily, but also enables future electric trucks to take advantage of regenerative braking to produce power rather than a long-haul trucks that will need to burn fuel to maintain highway speed. Electrified trucks will operate entirely on electric power in cities, reducing fuel consumed and air pollution.
A prototype new tractor-trailer has been built. Roush Engineering acted as general contractor using a number of different contractors to build the machine. The tractor was built by Peterbilt, the trailer by Great Dane and the microturbine engine by Capstone.
The design features a series-hybrid electric drive and small “micro” turbine engine. Much like a Chevy Volt, the truck can operate on electricity in urban areas for short distances up until the 45 kWh battery pack is down to 50 percent when the turbine engine will start to provide the electricity that the motor needs. There are a number of advantages to the Capstone C65 turbine. Its efficiency on natural gas is about 25-28 percent, boosted some by the electric drive. It has “air bearings” so that no oil is needed to operate the engine. No radiator is needed, so the chassis can be very streamlined. It is small and lightweight and can operate pretty much on anything that can burn – diesel, compressed natural gas, liquid natural gas and biofuels. It can also operate at one steady speed which can be optimized for efficiency. The driver can select a mode to charge the batteries while the vehicle is stationary.
Aerodynamics plays a big part in the efficiency of this big rig. Overall the streamlined truck has reduced drag by 20 percent. That yields a fuel efficiency increase of 10 percent on its own. The cab is placed over the engine bay and is on center. This makes for a shorter more efficient design, yet accommodates a sleeping area for the driver.
Great Dane Trailers was tapped to provide the cargo trailer. They designed and built the trailer almost entirely in carbon-fiber material. This saves 4,000 pounds of weight – more efficient when empty, and able to haul more cargo on deliveries. The forklift rating for the bed is 16,000 pounds. It too has an aerodynamically efficient design in a rounded nose, skirts and covered tires. It does not appear to use a tail cone, however. The tail cone is most effective in long-haul trucking – so I can see where they’d leave them off for all the short daily trips a distribution center truck does.
While not installed in the WAVE, General Electric has recently patented a combination fuel cell/turbine hybrid that reaches an efficiency of 70 percent. With this technology, natural gas can be both burned in the engine, and refined into hydrogen for the fuel cell during normal operation. Both then producing power for the electric drive motors to use. Mr. Green Car will be looking further into this and other trucking technology for a future report. R.